Transport Airplane Fuel Tank System Design Review, Flammability Reduction, and Maintenance and Inspection Requirements

SUMMARY: This proposed rulemaking would require design approval holders

of certain turbine-powered transport category airplanes to submit

substantiation to the FAA that the design of the fuel tank system of

previously certificated airplanes precludes the existence of ignition

sources within the airplane fuel tanks. It would also require the

affected design approval holders to develop specific fuel tank system

maintenance and inspection instructions for any items in the fuel tank

system that are determined to require repetitive inspections or

maintenance, to assure the safety of the fuel tank system. In addition,

the proposed rule would require certain operators of those airplanes to

incorporate FAA-approved fuel tank system maintenance and inspection

instructions into their current maintenance or inspection program.

Three amendments to the airworthiness standards for transport category

airplanes are also proposed. The first would define new requirements,

based on existing requirements, for demonstrating that ignition sources

could not be present in fuel tanks when failure conditions are

considered. The second would require future applicants for type

certification to identify any safety critical maintenance actions and

develop limitations to be placed in the instructions for continued

airworthiness for the fuel tank system. The third would require means

to minimize development of flammable vapors in fuel tanks, or means to

prevent catastrophic damage if ignition does occur. These actions are

the result of information gathered from accident investigations and

adverse service experience, which has shown that unforeseen failure

modes and lack of specific maintenance procedures on certain airplane

fuel tank systems may result in degradation of design safety features

intended to preclude ignition of vapors within the fuel tank.

DATES: Comments must be received on or before January 27, 2000.

ADDRESSES: Comments on this proposed rulemaking should be mailed or

delivered, in duplicate, to: U.S. Department of Transportation,

Dockets, Docket No. FAA-1999-6411, 400 Seventh Street SW., Room Plaza

401, Washington DC 20590. Comments may also be sent electronically to

the following Internet address: [email protected] Comments may be

filed and/or examined in Room Plaza 401 between 10 a.m. and 5 p.m.

weekdays, except Federal holidays. In addition, the FAA is maintaining

an information docket of comments in the Transport Airplane Directorate

(ANM-100), Federal Aviation Administration, Northwest Mountain Region,

1601 Lind Avenue SW., Renton, WA 98055-4056. Comments in the

information docket may be examined between 7:30 a.m. and 4:00 p.m.

weekdays, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Michael E. Dostert, FAA, Propulsion/

Mechanical/Crashworthiness Branch (ANM-112), Transport Airplane

Directorate, Aircraft Certification Service, 1601 Lind Avenue SW.,

Renton, Washington 98055-4056; telephone (425) 227-2132, facsimile

(425) 227-1320; e-mail: [email protected].

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in this proposed

rulemaking by submitting such written data, views, or arguments as they

may desire. Comments relating to the environmental, energy, federalism,

or economic impact that might result from adopting the proposals in

this notice are also invited. Substantive comments should be

accompanied by cost estimates. Commenters should identify the

regulatory docket or notice number and submit comments in duplicate to

the Docket address specified above. All comments received, as well as a

report summarizing each substantive public contact with FAA personnel

concerning this rulemaking, will be filed in the docket. All comments

received on or before the closing date will be considered by the

Administrator before taking action on this proposed rulemaking. Late

filed comments will be considered to the extent practicable. The

proposals contained in this notice may be changed in light of the

comments received. The Docket is available for public inspection before

and after the comment closing date. Commenters wishing the FAA to

acknowledge receipt of their comments submitted in response to this

notice must include with those comments a pre-addressed, stamped

postcard on which the following statement is made: ``Comments to Docket

No. FAA-1999-6411.'' The postcard will be date stamped and mailed to

the commenter.

Availability of the NPRM

An electronic copy of this document may be downloaded using a modem

and suitable communications software from the FAA regulations section

of the Fedworld electronic bulletin board service (telephone: 703-321-

3339), the Government Printing Office's electronic bulletin board

service (telephone: 202-512-1661), or the FAA's Aviation Rulemaking

Advisory Committee Bulletin Board service (telephone: (800) 322-2722 or

(202) 267-5948).

Internet users may reach the FAA's web page at http://www.faa.gov/

avr/arm/nprm/nprm.htm or the Government Printing Office's webpage at

http://www.access.gpo.gov/nara for access to recently published

rulemaking documents.

Any person may obtain a copy of this NPRM by submitting a request

to the Federal Aviation Administration, Office of Rulemaking, ARM-1,

800 Independence Avenue, SW., Washington, DC 20591, or by calling (202)

267-9680. Communications must identify the notice number or docket

number of this NPRM.

Persons interested in being placed on the mailing list for future

NPRM's should request from the above office a copy of Advisory Circular

No. 11-2A, Notice of Proposed Rulemaking Distribution System, that

describes the application procedure.

Background

On July 17, 1996, a 25-year old Boeing 747-100 series airplane was

involved in an inflight breakup after takeoff from Kennedy

International Airport in New York, resulting in 230 fatalities. The

accident investigation conducted by the National Transportation Safety

Board (NTSB) indicated that the center wing fuel tank exploded due to

an unknown ignition source. The NTSB has issued recommendations

intended to reduce heating of the fuel in the center wing fuel tanks on

the existing fleet of transport airplanes, reduce or eliminate

operation with flammable vapors in the fuel tanks of new type

certificated airplanes, and also to reevaluate the fuel system design

and maintenance practices on the fleet of transport airplanes. The

accident investigation

[[Page 58645]]

has now focused on mechanical failure as providing the energy source

that ignited the fuel vapors inside the tank. This accident has

prompted the FAA to examine the underlying safety issues surrounding

fuel tank explosions, the adequacy of the existing regulations, the

service history of airplanes certificated to these regulations, and

existing fuel tank system maintenance practices.

Flammability Characteristics

The flammability characteristics of the various fuels approved for

use in transport airplanes results in the presence of flammable vapors

in the vapor space of fuel tanks at various times during the operation

of the airplane. Vapors from Jet A fuel (the typical commercial

turbojet engine fuel) at temperatures below approximately 100 deg.F are

too lean to be flammable at sea level; at higher altitudes the fuel

vapors become flammable at temperatures above approximately 45 deg.F

(at 40,000 feet altitude). However, the regulatory authorities and

aviation industry have always presumed that a flammable fuel air

mixture exists in the fuel tanks at all times and have adopted the

philosophy that the best way to ensure airplane fuel tank safety is to

preclude ignition sources within fuel tanks. This philosophy has been

based on the application of fail-safe design requirements to the

airplane fuel tank system to preclude ignition sources from being

present in fuel tanks when component failures, malfunctions, or

lightning encounters occur. Possible ignition sources that have been

considered include electrical arcs, friction sparks, and autoignition.

(The autoignition temperature is the temperature at which the fuel/air

mixture will spontaneously ignite due to heat in the absence of an

ignition source.) Some events that could produce sufficient electrical

energy to create an arc include lightning, electrostatic charging,

electromagnetic interference (EMI), or failures in airplane systems or

wiring that introduce high-power electrical energy into the fuel tank

system. Friction sparks may be caused by mechanical contact between

certain rotating components in the fuel tank, such as a steel fuel pump

impeller rubbing on the pump inlet check valve. Autoignition of fuel

vapors may be caused by failure of components within the fuel tank, or

external components or systems that cause components or tank surfaces

to reach a high enough temperature to ignite the fuel vapors in the

fuel tank.

Existing Regulations/Certification Methods

The current 14 CFR part 25 regulations that are intended to require

designs that preclude the presence of ignition sources within the

airplane fuel tanks are as follows:

Section 25.901 is a general requirement that applies to all

portions of the propulsion installation, which includes the airplane

fuel tank system. It requires, in part, that the propulsion and fuel

tank systems be designed to ensure fail-safe operation between normal

maintenance and inspection intervals, and that the major components be

electrically bonded to the other parts of the airplane.

Airplane system fail-safe requirements are provided in

Secs. 25.901(c) and 25.1309. Section 25.901(c) requires that ``no

single failure or malfunction or probable combination of failures will

jeopardize the safe operation of the airplane.'' In general, the FAA's

policy has been to require applicants to assume the presence of

foreseeable latent (undetected) failure conditions when demonstrating

that subsequent single failures will not jeopardize the safe operation

of the airplane. Certain subsystem designs must also comply with

Sec. 25.1309, which requires airplane systems and associated systems to

be ``designed so that the occurrence of any failure condition which

would prevent the continued safe flight and landing of the airplane is

extremely improbable, and the occurrence of any other failure

conditions which would reduce the capability of the airplane or the

ability of the crew to cope with adverse operating conditions is

improbable.'' Compliance with Sec. 25.1309 requires an analysis, and

testing where appropriate, considering possible modes of failure,

including malfunctions and damage from external sources, the

probability of multiple failures and undetected failures, the resulting

effects on the airplane and occupants, considering the stage of flight

and operating conditions, and the crew warning cues, corrective action

required, and the capability of detecting faults.

This provision has the effect of mandating the use of ``fail-safe''

design methods which require that the effect of failures and

combinations of failures be considered in defining a safe design.

Detailed methods of compliance with Secs. 25.1309(b), (c), and (d) are

described in Advisory Circular (AC) 25.1309-1A, ``System Design

Analysis,'' and are intended as a means to evaluate the overall risk,

on average, of an event occurring within a fleet of aircraft. The

following guidance involving failures is offered in that AC:

1. In any system or subsystem, a single failure of any element or

connection during any one flight must be assumed without consideration

as to its probability of failing. This single failure must not prevent

the continued safe flight and landing of the airplane.

2. Additional failures during any one flight following the first

single failure must also be considered when the probability of

occurrence is not shown to be extremely improbable. The probability of

these combined failures includes the probability of occurrence of the

first failure.

As described in the AC, the FAA fail-safe design concept consists

of the following design principles or techniques intended to ensure a

safe design. The use of only one of these principles is seldom

adequate. A combination of two or more design principles is usually

needed to provide a fail-safe design (i.e., to ensure that catastrophic

failure conditions are not expected to occur during the life of the

fleet of a particular airplane model).

Design integrity and quality, including life limits, to

ensure intended function and prevent failures.

Redundancy or backup systems that provide system function

after the first failure (e.g., two or more engines, two or more

hydraulic systems, dual flight controls, etc.)

Isolation of systems and components so that failure of one

element will not cause failure of the other (sometimes referred to as

system independence).

Detection of failures or failure indication.

Functional verification (the capability for testing or

checking the component's condition).

Proven reliability and integrity to ensure that multiple

component or system failures will not occur in the same flight.

Damage tolerance that limits the safety impact or effect

of the failure.

Designed failure path that controls and directs the

failure, by design, to limit the safety impact.

Flightcrew procedures following the failure designed to

assure continued safe flight by specific crew actions.

Error tolerant design that considers probable human error

in the operation, maintenance, and fabrication of the airplane.

Margins of safety that allow for undefined and

unforeseeable adverse flight conditions.

These regulations, when applied to typical airplane fuel tank

systems, lead to a requirement for prevention of

[[Page 58646]]

ignition sources inside fuel tanks. The approval of the installation of

mechanical and electrical components inside the fuel tanks was

typically based on a qualitative system safety analysis and component

testing which showed: (1) that mechanical components would not create

sparks or high temperature surfaces in the event of any failure, and

(2) that electrical devices would not create arcs of sufficient energy

to ignite a fuel-air mixture in the event of a single failure or

probable combination of failures.

Section 25.901(b)(2) requires that the components of the propulsion

system be ``constructed, arranged, and installed so as to ensure their

continued safe operation between normal inspection or overhauls.''

Compliance with this regulation is typically demonstrated by

substantiating that the propulsion installation, which includes the

fuel tank system, will safely perform its intended function between

inspections and overhauls defined in the maintenance instructions.

Section 25.901(b)(4) requires electrically bonding the major

components of the propulsion system to the other parts of the airplane.

The affected major components of the propulsion system include the fuel

tank system. Compliance with this requirement for fuel tank systems has

been demonstrated by showing that all major components in the fuel tank

are electrically bonded to the airplane structure. This precludes

accumulation of electrical charge on the components and the possible

arcing in the fuel tank that could otherwise occur. In most cases,

electrical bonding is accomplished by installing jumper wires from each

major fuel tank system component to airplane structure. Advisory

Circular 25-8, ``Auxiliary Fuel Tank Installations,'' also provides

guidance for bonding of fuel tank system components and means of

precluding ignition sources within transport airplane fuel tanks.

Section 25.954 requires that the fuel tank system be designed and

arranged to prevent the ignition of fuel vapor within the system due to

the effects of lightning strikes. Compliance with this regulation is

typically shown by incorporation of design features such as minimum

fuel tank skin thickness, location of vent outlets out of likely

lightning strike areas, and bonding of fuel tank system structure and

components. Guidance for demonstrating compliance with this regulation

is provided in AC 20-53A, ``Protection of Aircraft Fuel Systems Against

Fuel Vapor Ignition Due to Lightning.''

Section 25.981 requires that the applicant determine the highest

temperature allowable in fuel tanks that provides a safe margin below

the lowest expected autoignition temperature of the fuel that is

approved for use in the fuel tanks. No temperature at any place inside

any fuel tank where fuel ignition is possible may then exceed that

maximum allowable temperature. This must be shown under all probable

operating, failure, and malfunction conditions of any component whose

operation, failure, or malfunction could increase the temperature

inside the tank. Guidance for demonstrating compliance with this

regulation has been provided in AC 25.981-1A, ``Guidelines For

Substantiating Compliance With the Fuel Tank Temperature

Requirements.'' The AC provides a listing of failure modes of fuel tank

system components that should be considered when showing that component

failures will not create a hot surface that exceeds the maximum

allowable fuel tank component or tank surface temperature for the fuel

type for which approval is being requested. Manufacturers have

demonstrated compliance with this regulation by testing and analysis of

components to show that design features, such as thermal fuses in fuel

pump motors, preclude an ignition source in the fuel tank when failures

such as a seized fuel pump rotor occur.

Airplane Maintenance Manuals and Instructions for Continued

Airworthiness

Historically, manufacturers have been required to provide

maintenance related information for fuel tank systems in the same

manner as for other systems. Prior to 1970, most manufacturers provided

manuals containing maintenance information for large transport category

airplanes, but there were no standards prescribing minimum content,

distribution, and a timeframe in which the information must be made

available to the operator. Section 25.1529, as amended by Amendment 25-

21 in 1970, required the applicant for a type certificate (TC) to

provide airplane maintenance manuals (AMM) to owners of the airplanes.

This regulation was amended in 1980 to require that the applicant for

type certification provide Instructions for Continued Airworthiness

(ICA) prepared in accordance with Appendix H to part 25. In developing

the ICA, the applicant is required to include certain information such

as a description of the airplane and its systems, servicing

information, and maintenance instructions, including the frequency and

extent of inspections necessary to provide for the continuing

airworthiness of the airplane (including the fuel tank system). As

required by Appendix H to part 25, the ICA must also include an FAA-

approved Airworthiness Limitations section enumerating those mandatory

inspections, inspection intervals, replacement times, and related

procedures approved under Sec. 25.571, relating to structural damage

tolerance. Currently the Airworthiness Limitations section of the ICA

applies only to airplane structure and not to the fuel tank system.

One method of establishing initial scheduled maintenance and

inspection tasks is the Maintenance Steering Group (MSG) process, which

develops a Maintenance Review Board (MRB) document for a particular

airplane model. Operators may incorporate those provisions, along with

other maintenance information contained in the ICA, into their

maintenance or inspection program.

Section 21.50 requires the holder of a design approval, including

the TC or supplemental type certificate (STC) for an airplane, aircraft

engine, or propeller for which application was made after January 28,

1981, to furnish at least one set of the complete ICA to the owner of

the product for which the application was made. The ICA for original

type certificated products must include instructions for the fuel tank

system. A design approval holder who has modified the fuel tank system

must furnish a complete set of the ICA for the modification to the

owner of the product.

Type Certificate Amendments Based on Major Change in Type Design

Over the years, many design changes have been introduced into fuel

tank systems that may affect their safety. There are three ways in

which major design changes can be approved: (1) the TC holder can apply

for an amendment to the type design; (2) any person, including the TC

holder, wanting to alter a product by introducing a major change in the

type design not great enough to require a new application for a TC, may

apply for an STC; and (3) in some instances a person may also make a

major alteration to the type design through a field approval. The field

approval process is a streamlined method for obtaining approval of

relatively simple modifications to airplanes. An FAA Flight Standards

Inspector can approve the alteration using Form FAA-337.

[[Page 58647]]

Maintenance and Inspection Program Requirements

Airplane operators are required to have extensive maintenance or

inspection programs that include provisions relating to fuel tank

systems.

Section 91.409(e), which generally applies to other than commercial

operations, requires an operator of a large turbojet multiengine

airplane or a turbopropeller-powered multiengined airplane to select

one of the following four inspection programs:

1. A continuous airworthiness inspection program that is part of a

continuous airworthiness maintenance program currently in use by a

person holding an air carrier operating certificate, or an operating

certificate issued under part 119 for operations under parts 121 or

135, and operating that make and model of airplane under those parts;

2. An approved airplane inspection program approved under

Sec. 135.419 and currently in use by a person holding an operating

certificate and operations specifications issued under part 119 for

part 135 operations;

3. A current inspection program recommended by the manufacturer; or

4. Any other inspection program established by the registered owner

or operator of that airplane and approved by the Administrator.

Section 121.367, which is applicable to those air carrier and

commercial operations covered by part 121, requires operators to have

an inspection program, as well as a program covering other maintenance,

preventative maintenance, and alterations.

Section 125.247, which is generally applicable to operation of

large airplanes, other than air carrier operations conducted under part

121, requires operators to inspect their airplanes in accordance with

an inspection program approved by the Administrator.

Section 129.14 requires a foreign air carrier and each foreign

operator of a U.S. registered airplane in common carriage, within or

outside the U.S., to maintain the airplane in accordance with an FAA-

approved program.

In general, the operators rely on the TC data sheet, MRB reports,

ICA's, the Airworthiness Limitations section of the ICA, other

manufacturers' recommendations, and their own operating experience to

develop the overall maintenance or inspection program for their

airplanes.

The intent of the rules governing the inspection and/or maintenance

program is to ensure that the inherent level of safety that was

originally designed into the system is maintained and that the airplane

is in an airworthy condition.

Historically, for fuel tank systems these required programs include

operational checks (e.g., preflight and enroute), functional checks

following maintenance actions (e.g., component replacement), overhaul

of certain components to prevent dispatch delays, and general zonal

visual inspections conducted concurrently with other maintenance

actions, such as structural inspections. However, specific maintenance

instructions to detect and correct conditions that degrade fail-safe

capabilities have not been deemed necessary because it has been assumed

that the original fail-safe capabilities would not be degraded in

service.

Design and Service History Review

The FAA has examined the service history of transport airplanes and

performed an analysis of the history of fuel tank explosions on these

airplanes. While there were a significant number of fuel tank fires and

explosions that occurred during the 1960's and 1970's on several

airplane types, in most cases the fire or explosion was found to be

related to design practices, maintenance actions, or improper

modification of fuel pumps. Some of the events were apparently caused

by lightning strikes. In most cases, an extensive design review was

conducted to identify possible ignition sources and actions were taken

that were intended to prevent similar occurrences. However, recent fuel

tank system related accidents have occurred in spite of these efforts.

On May 11, 1990, the center wing fuel tank of a Boeing 737-300

exploded while the airplane was on the ground at Nimoy Aquino

International Airport, Manila, Philippines. The airplane was less than

one year old. In the accident, the fuel-air vapors in the center wing

tank exploded as the airplane was being pushed back from a terminal

gate prior to flight. The accident resulted in 8 fatalities and

injuries to an additional 30 people. Accident investigators considered

a plausible scenario in which damaged wiring located outside the fuel

tank may have created a short between 115 volt airplane system wires

and 28 volt wires to a fuel tank level switch. This, in combination

with a possibly defective fuel level float switch, was investigated as

a possible source of ignition. However, a definitive ignition source

was never confirmed during the accident investigation. This unexplained

accident occurred on a newer airplane, in contrast to the July 17,

1996, accident which occurred on an older Boeing 747 airplane that was

approaching the end of its initial design life. These two accidents

indicate that the development of an ignition source inside the fuel

tank may be related to both the design and maintenance of the fuel tank

systems.

National Transportation Safety Board (NTSB) Recommendations

Since the July 17, 1996, accident, the FAA, NTSB, and aviation

industry have been reviewing the design features and service history of

the Boeing 747 and certain other transport airplane models. Based upon

its review, the NTSB has issued the following recommendations to the

FAA intended to reduce the exposure to operation with flammable vapors

in fuel tanks and address possible degradation of the original type

certificated fuel tank system designs on transport airplanes.

Reduced Flammability Exposure

A-96-174: Require the development of and implementation of design

or operational changes that will preclude the operation of transport-

category airplanes with explosive fuel-air mixtures in the fuel tanks:

Long Term Design Modifications:

(a) Significant consideration should be given to the development of

airplane design modification, such as nitrogen-inerting systems and the

addition of insulation between heat-generating equipment and fuel

tanks. Appropriate modifications should apply to newly certificated

airplanes and, where feasible, to existing airplanes.

A-96-175: Require the development of and implementation of design

or operational changes that will preclude the operation of transport-

category airplanes with explosive fuel-air mixtures in the fuel tanks:

Near Term Operational

(b) Pending implementation of design modifications, require

modifications in operational procedures to reduce the potential for

explosive fuel-air mixtures in the fuel tanks of transport-category

aircraft. In the B-747, consideration should be given to refueling the

center wing fuel tank (CWT) before flight whenever possible from cooler

ground fuel tanks, proper monitoring and management of the CWT fuel

temperature, and maintaining an appropriate minimum fuel quantity in

the CWT.

A-96-176: Require that the B-747 Flight Handbooks of TWA and other

operators of B-747s and other aircraft in which fuel tank temperature

cannot be determined by flightcrews be immediately revised to reflect

the

[[Page 58648]]

increases in CWT fuel temperatures found by flight tests, including

operational procedures to reduce the potential for exceeding CWT

temperature limitations.

A-96-177: Require modification of the CWT of B-747 airplanes and

the fuel tanks of other airplanes that are located near heat sources to

incorporate temperature probes and cockpit fuel tank temperature

displays to permit determination of the fuel tank temperatures.

Ignition Source Reduction

A-98-36: Conduct a survey of fuel quantity indication system probes

and wires in Boeing 747's equipped with systems other than Honeywell

Series 1-3 probes and compensators and in other model airplanes that

are used in Title 14 Code of Federal Regulations Part 121 service to

determine whether potential fuel tank ignition sources exist that are

similar to those found in the Boeing 747. The survey should include

removing wires from fuel probes and examining the wires for damage.

Repair or replacement procedures for any damaged wires that are found

should be developed.

A-98-38: Require in Boeing 747 airplanes, and in other airplanes

with fuel quantity indication system (FQIS) wire installations that are

co-routed with wires that may be powered, the physical separation and

electrical shielding of FQIS wires to the maximum extent possible.

A-98-39: Require, in all applicable transport airplane fuel tanks,

surge protection systems to prevent electrical power surges from

entering fuel tanks through fuel quantity indication system wires.

Service History

The FAA has also reviewed service difficulty reports for the

transport airplane fleet and evaluated the certification and design

practices utilized on these previously certificated airplanes. In

addition, an inspection of fuel tanks on Boeing 747 airplanes was

initiated. Representatives from the Air Transport Association (ATA),

Association of European Airlines (AEA), the Association of Asia Pacific

Airlines (AAPA), the Aerospace Industries Association of America, and

the Association Europeenne de Constructeurs de Materiel Aerospatial

(AECMA) initiated a joint effort to inspect and evaluate the condition

of the fuel tank system installations on a representative sample of

airplanes within the transport fleet. Data from initial inspections

conducted as part of this effort and shared with the FAA have assisted

in establishing a basis for developing corrective action for airplanes

within the transport fleet. In addition to the results from these

inspections, the FAA has received reports of anomalies on in-service

airplanes that have necessitated actions to preclude development of

ignition sources in or adjacent to airplane fuel tanks. The following

provides a summary of findings from design evaluations, service

difficulty reports, and a review of current airplane maintenance

practices.

Aging Airplane Related Phenomena

Fuel tank inspections initiated as part of the Boeing 747 accident

investigation identified aging of fuel tank system components,

contamination, corrosion of components and copper-sulfur deposits on

components as possible conditions that could contribute to development

of ignition sources within the fuel tanks. Results of detailed

inspection of the fuel pump wiring on several Boeing 747 airplanes

showed debris within the fuel tanks consisting of lockwire, rivets, and

metal shavings. Debris was also found inside scavenge pumps. Corrosion

and damage to insulation on FQIS probe wiring was found on wiring of 6

out of 8 probes removed from in-service airplanes. In addition,

inspection of airplane fuel tank system components from out-of-service

(retired) airplanes, initiated following the accident, revealed damaged

wiring and corrosion buildup of conductive copper-sulfur deposits on

the FQIS wiring on some Boeing 747 airplanes. The conductive deposits

or damaged wiring may result in a location where arcing could occur if

high power electrical energy was transmitted to the FQIS wiring from

another airplane source. While the effects of corrosion on fuel tank

system safety have not been fully evaluated, the FAA is developing a

research program to obtain a better understanding of the effects of

copper-sulfur deposits and corrosion on airplane fuel tank system

safety.

Wear or chafing of electrical power wires routed in conduits that

are located inside fuel tanks can result in arcing through the

conduits. On December 9, 1997, the FAA issued Airworthiness Directive

(AD) 96-26-06, applicable to certain Boeing 747 airplanes, which

required inspection of electrical wiring routed within conduits to fuel

pumps located in the wing fuel tanks and replacement of any damaged

wiring. Inspection reports indicated that many instances of wear had

occurred on Teflon sleeves installed over the wiring to protect it from

damage and possible arcing to the conduit.

Inspections of wiring to fuel pumps on Boeing 737 airplanes with

over 35,000 flight hours have shown significant wear to the insulation

of wires inside conduits that are located in fuel tanks. In nine

reported cases, wear resulted in arcing to the fuel pump wire conduit

on airplanes with greater than 50,000 flight hours. In one case, wear

resulted in burnthrough of the conduit into the interior of the 737

main tank fuel cell. On May 14, 1998, the FAA issued a telegraphic AD,

T98-11-52, which required inspection of wiring to Boeing 737 airplane

fuel pumps routed within electrical conduits and replacement of any

damaged wiring. Results of these inspections showed that wear of the

wiring occurred in many instances, particularly on those airplanes with

high numbers of flight cycles and operating hours.

The FAA has also received reports of corrosion on bonding jumper

wires within the fuel tanks on one in-service Airbus A300 airplane. The

manufacturer investigating this event did not have sufficient evidence

to determine conclusively the level of damage and corrosion found on

the jumper wires. Although the airplane was in long-term storage, it

does not explain why a high number of damaged/corroded jumper wires

were found concentrated in a specific area of the wing tanks. Further

inspections of a limited number of other Airbus models did not reveal

similar extensive corrosion or damage to bonding jumper wires. However,

they did reveal evidence of the accumulation of copper-sulfur deposits

around the outer braid of some jumper wires. Tests by the manufacturer

have shown that these deposits did not affect the bonding function of

the leads. Airbus has developed a one-time-inspection service bulletin

for all its airplanes to ascertain the extent of the copper-sulfur

deposits and to ensure that the level of jumper wire damage found on

the one A300 airplane is not widespread.

On March 30, 1998, the FAA received reports of three recent

instances of electrical arcing within fuel pumps installed in fuel

tanks on Lockheed L-1011 airplanes. In one case, the electrical arc had

penetrated the pump and housing and entered the fuel tank. Preliminary

investigation indicates that features incorporated into the fuel pump

design that were intended to preclude overheating and arc-through into

the fuel tank may not have functioned as intended due to discrepancies

introduced during overhaul of the pumps. Emergency AD 98-08-09 was

issued April 3, 1998, to specify a minimum quantity of fuel to be

carried in the fuel tanks for the purpose of

[[Page 58649]]

covering the pumps with liquid fuel and thereby precluding ignition of

vapors within the fuel tank until such time as terminating corrective

action could be developed.

Unforeseen Fuel Tank System Failures

After an extensive review of the Boeing 747 design following the

July 17, 1996, accident, the FAA determined that during original

certification of the fuel tank system, the degree of tank contamination

and the significance of certain failure modes of fuel tank system

components had not been considered to the degree that more recent

service experience indicates is needed. For example, in the absence of

contamination, the FQIS had been shown to preclude creating an arc if

FQIS wiring were to come in contact with the highest level of

electrical voltage on the airplane. This was shown by demonstrating

that the voltage needed to cause an arc in the fuel probes due to an

electrical short condition was well above any voltage level available

in the airplane systems. However, recent testing has shown that if

contamination, such as conductive debris (lock wire, nuts, bolts, steel

wool, corrosion, copper-sulfur deposits, metal filings, etc.) is placed

within gaps in the fuel probe, the voltage needed to cause an arc is

within values that may occur due to a subsequent electrical short or

induced current on the FQIS probe wiring from electromagnetic

interference caused by adjacent wiring. These anomalies, by themselves,

could not lead to an electrical arc within the fuel tanks without the

presence of an additional failure. If any of these anomalies were

combined with a subsequent failure within the electrical system that

creates an electrical short, or if high-intensity radiated fields

(HIRF) or electrical current flow in adjacent wiring induces EMI

voltage in the FQIS wiring, sufficient energy could enter the fuel tank

and cause an ignition source within the tank.

On November 26, 1997, in Docket No. 97-NM-272-AD, the FAA proposed

a requirement for operators of Boeing 747-100, -200, and -300 series

airplanes to install components for the suppression of electrical

transients and/or the installation of shielding and separation of fuel

quantity indicating system wiring from other airplane system wiring.

After reviewing the comments received on the proposed requirements, the

FAA issued AD 98-20-40 on September 23, 1998 that requires the

installation of shielding and separation of the electrical wiring of

the fuel quantity indication system. On April 14, 1998, the FAA

proposed a similar requirement for Boeing 737-100, -200, -300, -400,

and -500 series airplanes in Docket No. 98-NM-50-AD, which led to the

FAA issuing AD 99-03-04 on January 26, 1999. The FAA action required in

those two airworthiness directives is intended to preclude high levels

of electrical energy from entering the airplane fuel tank wiring due to

electromagnetic interference or electrical shorts. All later model

Boeing 747 and 737 FQIS's have wire separation and fault isolation

features that may meet the intent of these AD actions. This proposed

rulemaking will require evaluation of these later designs.

Other examples of unanticipated failure conditions include

incidents of parts from fuel pump assemblies impacting or contacting

the rotating fuel pump impeller. The first design anomaly was

identified when two incidents of damage to fuel pumps were reported on

Boeing 767 airplanes. In both cases objects from a fuel pump inlet

diffuser assembly were ingested into the fuel pump, causing damage to

the pump impeller and pump housing. The damage could have caused sparks

or hot debris from the pump to enter the fuel tank. To address this

unsafe condition, the FAA issued AD 97-19-15. This AD requires revision

of the airplane flight manual to include procedures to switch off the

fuel pumps when the center tank approaches empty. The intent of this

interim action is to maintain liquid fuel over the pump inlet so that

any debris generated by a failed fuel pump will not come in contact

with fuel vapors and cause a fuel tank explosion.

The second design anomaly was reported on Boeing 747-400 series

airplanes. The reports indicated that inlet adapters of the override/

jettison pumps of the center wing fuel tank were found to be worn. Two

of the inlet adapters had worn down enough to cause damage to the

rotating blades of the inducer. The inlet check valves also had

significant damage. Another operator reported damage to the inlet

adapter that was so severe that contact had occurred between the steel

disk of the inlet check valve and the steel screw that holds the

inducer in place. Wear to the inlet adapters has been attributed to

contact between the inlet check valve and the adapter. Such excessive

wear of the inlet adapter can lead to contact between the inlet check

valve and inducer, which could result in pieces of the check valve

being ingested into the inducer and damaging the inducer and impellers.

Contact between the steel disk of the inlet check valve and the steel

rotating inducer screw can cause sparks. To address this unsafe

condition, the FAA issued an immediately adopted rule, AD 98-16-19, on

July 30, 1998.

Another design anomaly was reported in 1989 when a fuel tank

ignition event occurred in an auxiliary fuel tank during refueling of a

Beech 400 airplane. The auxiliary fuel tank had been installed under an

STC. Polyurethane foam had been installed in portions of the tank to

minimize the potential of a fuel tank explosion if uncontained engine

debris penetrated those portions of the tank. The accident

investigation indicated that electrostatic charging of the foam during

refueling resulted in ignition of fuel-air vapors in portions of the

adjacent fuel tank system that did not contain the foam. The fuel vapor

explosion caused distortion of the tank and fuel leakage from a failed

fuel line. Modifications to the design, including use of more

conductive polyurethane foam and installation of a standpipe in the

refueling system, were incorporated to prevent reoccurrence of

electrostatic charging and resulting fuel tank ignition source.

Review of Fuel Tank System Maintenance Practices

In addition to the review of the design features and service

history of the Boeing 747 and other airplane models in the transport

airplane fleet, the FAA has also reviewed the current fuel tank system

maintenance practices for these airplanes.

Typical transport category airplane fuel tank systems are designed

with redundancy and fault indication features such that single

component failures do not result in any significant reduction in

safety. Therefore, fuel tank systems historically have not had any

life-limited components or specific detailed inspection requirements,

unless mandated by airworthiness directives. Most of the components are

``on condition,'' meaning that some test, check, or other inspection is

performed to determine continued serviceability, and maintenance is

performed only if the inspection identifies a condition requiring

correction. Visual inspection of fuel tank system components is by far

the predominant method of inspection for components such as boost

pumps, fuel lines, couplings, wiring, etc. Typically these inspections

are conducted concurrently with zonal inspections or internal or

external fuel tank structural inspections. These inspections normally

do not provide information regarding the continued serviceability of

components within the fuel tank system, unless the visual inspection

indicates a potential problem

[[Page 58650]]

area. For example, it would be difficult, if not impossible, to detect

certain degraded fuel tank system conditions, such as worn wiring

routed through conduit to fuel pumps, debris inside fuel pumps,

corrosion to bonding wire interfaces, etc., without dedicated intrusive

inspections that are much more extensive than those normally conducted.

Listing of Deficiencies

The list provided below summarizes fuel tank system design

features, malfunctions, failures, and maintenance related actions that

have been identified through service experience to result in a

degradation of the safety features of airplane fuel tank systems. This

list was developed from service difficulty reports and incident and

accident reports. These anomalies occurred on in-service transport

category airplanes contrary to the intent of regulations and policies

intended to preclude the development of ignition sources within

airplane fuel tank systems.

1. Pumps:

Ingestion of the pump inducer into the pump impeller and

generation of debris into the fuel tank.

Pump inlet case degradation, allowing the pump inlet check

valve to contact the impeller.

Stator winding failures during operation of the fuel pump.

Subsequent failure of a second phase of the pump resulting in arcing

through the fuel pump housing.

Deactivation of thermal protective features incorporated

into the windings of pumps due to inappropriate wrapping of the

windings.

Omission of cooling port tubes between the pump assembly

and the pump motor assembly during fuel pump overhaul.

Extended dry running of fuel pumps in empty fuel tanks,

which was contrary to the manufacturer's recommended procedures.

Use of steel impellers that may produce sparks if debris

enters the pump.

Debris lodged inside pumps.

Arcing due to the exposure of electrical connections

within the pump housing that have been designed with inadequate

clearance to the pump cover.

Thermal switches resetting over time to a higher trip

temperature.

Flame arrestors falling out of their respective mounting.

Internal wires coming in contact with the pump rotating

group, energizing the rotor and arcing at the impeller/adapter

interface.

Poor bonding across component interfaces.

Insufficient ground fault current protection capability.

Poor bonding of components to structure.

2. Wiring to pumps in conduits located inside fuel tanks:

Wear of Teflon sleeving and wiring insulation allowing

arcing from wire through metallic conduits into fuel tanks.

3. Fuel pump connectors:

Electrical arcing at connections within electrical

connectors due to bent pins or corrosion.

Fuel leakage and subsequent fuel fire outside of the fuel

tank caused by corrosion of electrical connectors inside the pump motor

which lead to electrical arcing through the connector housing

(connector was located outside the fuel tank).

Selection of improper materials in connector design.

4. FQIS wiring:

Degradation of wire insulation (cracking), corrosion and

copper-sulfur deposits at electrical connectors.

Unshielded FQIS wires routed in wire bundles with high

voltage wires.

5. FQIS probes:

Corrosion and copper-sulfur deposits causing reduced

breakdown voltage in FQIS wiring.

Terminal block wiring clamp (strain relief) features at

electrical connections on fuel probes causing damage to wiring

insulation.

Contamination in the fuel tanks causing reduced arc path

between FQIS probe walls (steel wool, lock wire, nuts, rivets, bolts;

mechanical impact damage to probes).

6. Bonding straps:

Corrosion to bonding straps.

Loose or improperly grounded attachment points.

Static bonds on fuel tank system plumbing connections

inside the fuel tank worn due to mechanical wear of the plumbing from

wing movement and corrosion.

7. Electrostatic charge:

Use of non-conductive reticulated polyurethane foam that

holds electrostatic charge buildup.

Spraying of fuel into fuel tanks through inappropriately

designed refueling nozzles or pump cooling flow return methods.

Fuel Tank Flammability

In addition to the review of potential fuel tank ignition, the FAA

has undertaken a parallel effort to address the threat of fuel tank

explosions by eliminating or significantly reducing the presence of

explosive fuel air mixtures within the fuel tanks of new type designs,

in-production, and the existing fleet of transport airplanes. On April

3, 1997, the FAA published a notice in the Federal Register (62 FR

16014) that requested comments concerning the 1997 NTSB recommendations

regarding reduced flammability listed earlier in this notice. That

notice provided significant discussion of service history, background,

and issues relating to reducing flammability in transport airplane fuel

tanks. Comments received from that notice indicated that additional

information was needed before the FAA could initiate rulemaking action

to address the recommendations.

On January 23, 1998, the FAA published a notice in the Federal

Register that established an Aviation Rulemaking Advisory Committee

(ARAC) working group, the Fuel Tank Harmonization Working Group

(FTHWG), tasked to achieve this goal. The ARAC consists of interested

parties, including the public, and provides a public process for advice

to be given to the FAA concerning development of new regulations. The

FTHWG evaluated numerous possible means of reducing or eliminating

hazards associated with explosive vapors in fuel tanks. On July 23,

1998, the ARAC submitted its report to the FAA. The full report has

been placed in a docket that was created for this ARAC working group

(Docket No. FAA-1998-4183). That docket can be reviewed on the U.S.

Department of Transportation electronic Document Management System on

the Internet at http://dms.dot.gov. The full report has also been

placed in the docket for this rulemaking.

The report provided a recommendation for the FAA to initiate

rulemaking action to amend Sec. 25.981, applicable to new type design

airplanes, to include a requirement to limit the time transport

airplane fuel tanks could operate with flammable vapors in the vapor

space of the tank. The recommended regulatory text proposed, ``Limiting

the development of flammable conditions in the fuel tanks, based on the

intended fuel types, to less than 7 percent of the expected fleet

operational time, or providing means to mitigate the effects of an

ignition of fuel vapors within the fuel tanks such that any damage

caused by an ignition will not prevent continued safe flight and

landing.'' The report discussed various options of showing compliance

with this proposal, including managing heat input to the fuel tanks,

installation of inerting systems or polyurethane fire suppressing foam,

and suppressing an explosion if one occurred, etc.

The level of flammability defined in the proposal was established

based

[[Page 58651]]

upon comparison of the safety record of center wing fuel tanks that, in

certain airplanes, are heated by equipment located under the tank, and

unheated fuel tanks located in the wing. The FTHWG concluded that the

safety record of fuel tanks located in the wings was adequate and that

if the same level could be achieved in center wing fuel tanks, the

overall safety objective would be achieved. Results from thermal

analyses documented in the report indicate that center wing fuel tanks

that are heated by air conditioning equipment located beneath them are

flammable, on a fleet average basis, for up to 30 percent of the fleet

operating time.

During the ARAC process it was also determined that certain

airplane types do not locate heat sources adjacent to the fuel tanks.

These airplanes provide significantly reduced flammability exposure,

near the 5 percent value of the wing tanks. The group therefore

determined that it would be feasible to design new airplanes such that

fuel tank operation in the flammable range would be limited to near

that of the wing fuel tanks. The primary method of compliance with the

requirement proposed by the ARAC would likely be to control heat

transfer into and out of fuel tanks such that heating of the fuel would

not occur. Design features such as locating the air conditioning

equipment away from the fuel tanks, providing ventilation of the air

conditioning bay to limit heating and cool fuel tanks, and/or

insulating the tanks from heat sources, would be practical means of

complying with the regulation proposed by the ARAC.

In addition to its recommendation to revise Sec. 25.981, the ARAC

also recommended that the FAA continue to evaluate means for minimizing

the development of flammable vapors within the fuel tanks to determine

whether other alternatives, such as ground based inerting of fuel

tanks, could be shown to be cost effective.

Discussion of the Proposal

The FAA review of the service history, design features, and

maintenance instructions of the transport airplane fleet indicates that

aging of fuel tank system components and unforeseen fuel tank system

failures and malfunctions have become a safety issue for the fleet of

turbine-powered transport category airplanes. The FAA proposes to amend

the current regulations in four areas.

The first area of concern encompasses the possibility of the

development of ignition sources within the existing transport airplane

fleet. Many of the design practices used on airplanes in the existing

fleet are similar. Therefore anomalies that have developed on specific

airplane models within the fleet could develop on other airplane

models. As a result, the FAA considers that a one-time design review of

the fuel tank system for transport airplane models in the current fleet

is needed.

The second area of concern encompasses the need to require the

design of future transport category airplanes to more completely

address potential failures in the fuel tank system that could result in

an ignition source in the fuel tank system.

Third, certain airplane types are designed with heat sources

adjacent to the fuel tank, which results in heating of the fuel and a

significant increase in the formation of flammable vapors in the tank.

The FAA considers that fuel tank safety can be enhanced by reducing the

time fuel tanks operate with flammable vapors in the tank and is

therefore proposing a requirement to provide means to minimize the

development of flammable vapors in fuel tanks or provide means to

prevent catastrophic damage if ignition does occur.

Fourth, the FAA considers that it is necessary to impose

operational requirements so that any required maintenance or inspection

actions will be included in each operator's FAA-approved program.

Proposed SFAR

Historically, the FAA has worked together with the TC holders when

safety issues arise to identify solutions and actions that need to be

taken. Some of the safety issues that have been addressed by this

voluntary cooperative process include those involving aging aircraft

structure, thrust reversers, cargo doors, and wing icing protection.

While some manufacturers have aggressively completed these safety

reviews, others have not applied the resources necessary to complete

these reviews in a timely manner, which delayed the adoption of

corrective action. Although these efforts have frequently been

successful in achieving the desired safety objectives, a more uniform

and expeditious response is considered necessary to address fuel tank

safety issues.

While maintaining the benefits of FAA-TC holder cooperation, the

FAA considers that a Special Federal Aviation Regulation (SFAR)

provides a means for the FAA to establish clear expectations and

standards, as well as a timeframe within which the design approval

holders and the public can be confident that fuel tank safety issues on

the affected airplanes will be uniformly examined.

This proposed rulemaking is intended to ensure that the design

approval holder completes a comprehensive assessment of the fuel tank

system and develops any required inspections, maintenance instructions,

or modifications.

Safety Review

The proposed SFAR would require the design approval holder to

perform a safety review of the fuel tank system to show that fuel tank

fires or explosions will not occur on airplanes of the approved design.

In conducting the review, the design approval holder would be required

to demonstrate compliance with the standards proposed in this notice

for Sec. 25.981(a) and (b) (discussed below) and the existing standards

of Sec. 25.901. As part of this review, the design approval holder

would be required to submit a report to the cognizant FAA Aircraft

Certification Office (ACO) that substantiates that the fuel tank system

is fail-safe.

The FAA intends that those failure conditions listed previously in

this notice, and any other foreseeable failures, should be assumed when

performing the system safety analysis needed to substantiate that the

fuel tank system design is fail-safe. The system safety analysis should

be prepared considering all airplane inflight, ground, service, and

maintenance conditions, assuming that an explosive fuel air mixture is

present in the fuel tanks at all times, unless the fuel tank has been

purged of fuel vapor for maintenance. The design approval holder would

be expected to develop a failure modes and effects analysis (FMEA) for

all components in the fuel tank system. Analysis of the FMEA would then

be used to determine whether single failures, alone or in combination

with foreseeable latent failures, could cause an ignition source to

exist in a fuel tank. A subsequent quantitative fault tree analysis

should then be developed to determine whether combinations of failures

expected to occur in the life of the affected fleet could cause an

ignition source to exist in a fuel tank system.

Because fuel tank systems typically have few components within the

fuel tank, the number of possible sources of ignition is limited. The

system safety analysis required by this proposed rule would include all

components or systems that could introduce a source of fuel tank

ignition. This may require analysis of not only the fuel tank system

components, (e.g., pumps, fuel pump power supplies, fuel valves, fuel

quantity indication system probes,

[[Page 58652]]

wiring, compensators, densitometers, fuel level sensors, etc.), but

also other airplane systems that may affect the fuel tank system. For

example, failures in airplane wiring or electromagnetic interference

from other airplane systems could cause an ignition source in the

airplane fuel tank system under certain conditions and therefore would

have to be included in the system safety analysis. A proposed revision

to AC 25.981-1A, discussed later in this document, is being developed

to provide guidance on performing the safety review.

The intent of the design review proposed in this notice is to

assure that each fuel tank system design that is affected by this

action will be fully assessed and that the design approval holder

identifies any required modifications, added flight deck or maintenance

indications, and/or maintenance actions necessary to meet the fail-safe

criteria.

Maintenance Instructions

The FAA anticipates that the safety review would identify critical

areas of the fuel tank and other related systems that would require

maintenance actions to account for the affects of aging, wear,

corrosion, and possible contamination on the fuel tank system. For

example, service history indicates that copper-sulfur deposits may form

on fuel tank components, including bonding straps and FQIS components,

which could degrade the intended design capabilities by providing a

mechanism by which arcing could occur. Therefore, it might be necessary

to provide maintenance instructions to identify and eliminate such

deposits.

The proposed SFAR would require that the design approval holder

develop any specific maintenance and inspection instructions necessary

to maintain the design features required to preclude the existence or

development of an ignition source within the fuel tank system. These

instructions would have to be established to ensure that an ignition

source will not develop throughout the remaining operational life of

the airplane.

Possible Airworthiness Directives

The design review may also result in identification of unsafe

conditions on certain airplane models that would require issuance of

airworthiness directives. For example, as discussed previously in this

notice, the FAA has required or proposed requirements for design

changes to the Boeing 737, 747, and 767; Boeing Douglas Products

Division DC-10 and Lockheed L-1011 airplanes. Design practices utilized

on these models may be similar to those of other airplane types;

therefore, the FAA expects that modifications to airplanes with similar

design features may also be required.

The number and scope of any possible AD's may vary by airplane type

design. For example, wiring separation and shielding of FQIS wires on

newer technology airplanes significantly reduces the likelihood of an

electrical short causing an electrical arc in the fuel tank; many newer

transport airplanes do not route electrical power wiring to fuel pumps

inside the airplane fuel tanks. Therefore, some airplane models may not

require significant modifications or additional dedicated maintenance

procedures. Other models may require significant modifications or more

maintenance. For example, the FQIS wiring on some older technology

airplanes is routed in wire bundles with high voltage power supply

wires. The original failure analyses conducted on these airplane types

did not consider the possibility that the fuel quantity indication

system may become degraded allowing a significantly lower voltage level

to produce a spark inside the fuel tank. Causes of degradation observed

in service include aging, corrosion, or undetected contamination of the

system. As previously discussed, the FAA has issued AD actions for

certain Boeing 737 and 747 airplanes to address this condition.

Modification of similar types of installations on other airplane models

may be required to address this unsafe condition and to achieve a fail-

safe design.

It should be noted that any design changes may, in themselves,

require maintenance actions. For example, transient protection devices

typically require scheduled maintenance in order to detect latent

failure of the suppression feature. As a part of the required design

review, the manufacturer would define the necessary maintenance

procedures and intervals for any required maintenance actions.

Applicability of the Proposed SFAR

As proposed, the SFAR would apply to holders of TCs, and STCs for

modifications that affect the fuel tank systems of turbine-powered

transport category airplanes, for which the TC was issued after January

1, 1958, and the airplane has a maximum type certificated passenger

capacity of 30 or more, or a maximum type certificated payload capacity

of 7500 pounds or more. The SFAR would also apply to applicants for

type certificates, amendments to a type certificate, and supplemental

type certificates affecting the fuel tank systems for those airplanes

identified above if the application was filed before the effective date

of the proposed SFAR and the certificate was not issued before the

effective date of the SFAR. The FAA has determined that turbine-powered

airplanes, regardless of whether they are turboprops or turbojets,

should be subject to the rule, because the potential for ignition

sources in fuel tank systems is unrelated to the engine design. This

would result in the coverage of the large transport category airplanes

where the safety benefits and public interest are greatest. This action

would affect approximately 6,000 U.S. registered airplanes in part 91,

121, 125, and 129 operations.

The date January 1, 1958, was chosen so that only turbine-powered

airplanes, except for a few 1953-1958 vintage Convair 340s and 440s

converted from reciprocating power, would be included. No

reciprocating-powered transport category airplanes are known to be used

currently in passenger service, and the few remaining in cargo service

would be excluded. Compliance is not proposed for those older airplanes

because their advanced age and small numbers would likely make

compliance impractical from an economic standpoint. This is consistent

with similar exclusions made for those airplanes from other

requirements applicable to existing airplanes, such as the regulations

adopted for flammability of seat cushions (49 FR 43188, October 24,

1984); flammability of cabin interior components (51 FR 26206, July 21,

1986); cargo compartment liners (54 FR 7384, February 17, 1989); access

to passenger emergency exits (57 FR 19244, May 4, 1992); and Class D

cargo or baggage compartments (63 FR 8032, February 17, 1998).

In order to achieve the benefits of this rulemaking for large

transport airplanes as quickly as possible, the FAA has decided to

proceed with this rulemaking with the applicability of the SFAR limited

to airplanes with a maximum certificated passenger capacity of at least

30 or at least 7,500 pounds payload. Compliance is not proposed for

smaller airplanes because it is not clear at this time that the

possible benefits for those airplanes would be commensurate with the

costs involved. However, the FAA intends to undertake a full regulatory

evaluation of applying these requirements to small transport category

and commuter category airplanes to determine the merits of subsequently

extending the rule to airplanes with a passenger capacity of fewer than

30 and less than 7,500 pounds payload. Therefore, the FAA specifically

requests comments as to the feasibility of

[[Page 58653]]

requiring holders of type certificates issued prior to January 1, 1958,

or for airplanes having a passenger capacity of fewer than 30 and less

than 7,500 pounds payload, to comply and the safety benefits likely to

be realized.

Supplemental Type Certificates (STC)

The FAA considers that this rule should apply to STC holders as

well, because a significant number of STCs effect changes to fuel tank

systems, and the objectives of this proposed rule would not be achieved

unless these systems are also reviewed and their safety ensured. The

service experience noted in the background of this proposed rule

indicates modifications to airplane fuel tank systems incorporated by

STCs may affect the safety of the fuel tank system.

Modifications that could affect the fuel tank system include those

that could result in an ignition source in the fuel tank. Examples

include installation of auxiliary fuel tanks and installation of, or

modification to, other systems such as the fuel quantity indication

system, the fuel pump system (including electrical power supply),

airplane refueling system, any electrical wiring routed within or

adjacent to the fuel tank, and fuel level sensors or float switches.

Modifications to systems or components located outside the fuel tank

system may also affect fuel tank safety. For example, installation of

electrical wiring for other systems that was inappropriately routed

with FQIS wiring could violate the wiring separation requirements of

the type design. Therefore, the FAA intends that a fuel tank system

safety review be conducted for any modification to the airplane that

may affect the safety of the fuel tank system. The level of evaluation

that is intended would be dependent upon the type of modification. In

most cases a simple qualitative evaluation of the modification in

relation to the fuel tank system, and a statement that the change has

no effect on the fuel tank system, would be all that is necessary. In

other cases where the initial qualitative assessment shows that the

modification may affect the fuel tank system, a more detailed safety

review would be required.

Design approvals for modification to airplane fuel tank systems

approved by STCs require the applicant to have knowledge of the

airplane fuel tank system in which the modification is installed. The

majority of these approvals are held by the original airframe

manufacturers or airplane modifiers that specialize in fuel tank system

modifications, such as installation of auxiliary fuel tanks. Therefore,

the FAA expects that the data needed to complete the safety review

proposed in this notice would be available to the STC holder.

Compliance

This notice proposes a 12-month compliance time from the effective

date of the final rule, or within 12 months after the issuance of a

certificate for which application was filed before the effective date

of this SFAR, whichever is later, for design approval holders to

conduct the safety review and develop the compliance documentation and

any required maintenance and inspection instructions. The FAA would

expect each design approval holder to work with the cognizant FAA

Aircraft Certification Office (ACO) and Aircraft Evaluation Group (AEG)

to develop a plan to complete the safety review and develop the

required maintenance and inspection instructions within the 12 month

period. The plan should include periodic reviews with the ACO and AEG

of the ongoing safety review and the associated maintenance and

inspection instructions.

During the proposed 12-month compliance period, the FAA is

committed to working with the affected design approval holders to

assist them in complying with the requirements of this proposed SFAR.

However, failure to comply within the specified time would constitute a

violation of the proposed requirements and may subject the violator to

certificate action to amend, suspend, or revoke the affected

certificate in accordance with 49 U.S.C. Sec. 44709. It may also

subject the violator to a civil penalty of not more than $1,100 per day

until the SFAR is complied with, in accordance with 49 U.S.C.

Sec. 46301.

Proposed Operating Requirements

This proposed rule would require that affected operators

incorporate FAA-approved fuel tank system maintenance and inspection

instructions in their maintenance or inspection program within 18

months of the effective date of the proposed rule. If the design

approval holder has complied with the SFAR and developed an FAA-

approved program, the operator could incorporate that program to meet

the proposed requirement. The operator would also have the option of

developing its own program independently, and would be ultimately

responsible for having an FAA-approved program, regardless of the

action taken by the design approval holder.

The proposed rule would prohibit the operation of certain transport

category airplanes operated under parts 91, 121, 125, and 129 beyond a

specified compliance time, unless the operator of those airplanes has

incorporated FAA-approved fuel tank maintenance and inspection

instructions in its maintenance or inspection program, as applicable.

The proposed regulation would require that the maintenance and

inspection instructions be approved by the Administrator; for the

purposes of this rule, the Administrator is considered to be the

manager of the cognizant FAA ACO.

The operator would need to consider the following:

1. The fuel tank system maintenance and inspection instructions

that would be incorporated into the operator's existing maintenance or

inspection program would need to be approved by the FAA ACO having

cognizance over the TC of the airplane. If the operator can establish

that the existing maintenance and inspection instructions fulfill the

requirements of this proposed rule, then the ACO may approve the

operator's existing maintenance and inspection instructions without

change.

2. The means by which the FAA-approved fuel tank system maintenance

and inspection instructions would be incorporated into a certificate

holder's FAA-approved maintenance or inspection program would be

subject to approval by the certificate holder's principal maintenance

inspector (PMI) or other cognizant airworthiness inspector. The FAA

intends that any escalation to the FAA-approved inspection intervals

would require the operator to receive FAA approval of the amended

program. Any request for escalation to the FAA approved inspection

intervals would need to include data to substantiate that the proposed

interval will provide the level of safety intended by the original

approval. If inspection results and service experience indicate that

additional or more frequent inspections are necessary, the FAA may

issue AD's to mandate such changes to the inspection program.

3. This rule would not impose any new reporting requirements;

however, normal reporting required under 14 CFR Secs. 121.703 and

125.409 would still apply.

4. This rule would not impose any new FAA recordkeeping

requirements. However, as with all maintenance, the current operating

regulations (e.g., 14 CFR Secs. 121.380 and 91.417) already impose

recordkeeping requirements that would apply to the actions required by

this proposed rule. When incorporating the fuel tank system maintenance

and inspection instructions into its

[[Page 58654]]

approved maintenance or inspection program, each operator should

address the means by which it will comply with these recordkeeping

requirements. That means of compliance, along with the remainder of the

program, would be subject to approval by the cognizant PMI or other

cognizant airworthiness inspector.

5. The maintenance and inspection instructions developed by the TC

holder under the proposed rule generally would not apply to fuel tank

systems modified by an STC, including any auxiliary fuel tank

installations or other modifications. The operator, however, would

still be responsible to incorporate specific maintenance and inspection

instructions applicable to the entire fuel tank system that meet the

requirements of this proposed rulemaking. This means that the operator

should evaluate the fuel tank systems and any alterations to the fuel

tank system and then develop, submit, and gain FAA approval of the

maintenance and inspection instructions to evaluate repairs to such

fuel tank systems.

The FAA recognizes that operators may not have the resources to

develop maintenance or inspection instructions for the airplane fuel

tank system. The proposed rule would therefore require the TC and STC

holders to develop fuel tank system maintenance and inspection

instructions that may be used by operators. If however, the STC holder

is out of business or otherwise unavailable, the operator would

independently have to acquire the FAA-approved inspection instructions.

To keep the airplanes in service, operators, either individually or as

a group, could hire the necessary expertise to develop and gain

approval of maintenance and inspection instructions. Guidance on how to

comply with this aspect of the proposed rule would be provided in the

planned revision to AC 25.981-1A.

After the PMI having oversight responsibilities is satisfied that

the operator's continued airworthiness maintenance or inspection

program contains all of the elements of the FAA-approved fuel tank

system maintenance and inspection instructions, the airworthiness

inspector would approve the maintenance or inspection program revision.

This approval would have the effect of requiring compliance with the

maintenance and inspection instructions.

Applicability of the Proposed Operating Requirements

This proposed rule would prohibit the operation of certain

transport category airplanes operated under 14 CFR parts 91, 121, 125,

and 129 beyond a specified compliance time, unless the operator of

those airplanes has incorporated FAA-approved specific maintenance and

inspection instructions applicable to the fuel tank system in its

approved maintenance or inspection program, as applicable. The

operational applicability was established so that all airplane types

affected by the SFAR, regardless of type of operation, would be subject

to FAA approved fuel tank system maintenance and inspection procedures.

As discussed earlier, this proposed rulemaking would include each

turbine-powered transport category airplane model, provided its TC was

issued after January 1, 1958, and it has a maximum type certificated

passenger capacity of 30 or more, or a maximum type certificated

payload capacity of 7,500 pounds or more.

Field Approvals

A significant number of changes to other transport category

airplane fuel tank systems have been incorporated through field

approvals issued to the operators of those airplanes. These changes may

also significantly affect the safety of the fuel tank system. The

operator of any airplane with such changes would be required to develop

the fuel tank system maintenance and inspection program instructions

and submit it to the FAA for approval, together with the necessary

substantiation of compliance with the design review requirements of the

SFAR.

Compliance

This notice proposes an 18 month compliance time from the effective

date of the final rule for operators to incorporate FAA-approved long

term fuel tank system maintenance and inspection instructions into

their approved program. The FAA would expect each operator to work with

the airplane TC holder or STC holder to develop a plan to implement the

required maintenance and inspection instructions within the 18 month

period. The plan should include periodic reviews with the cognizant ACO

and AEG that would approve the associated maintenance and inspection

instructions.

Proposed Changes to Part 25

Currently, Sec. 25.981 defines limits on surface temperatures

within transport airplane fuel tank systems. In order to address future

airplane designs, the FAA proposes to revise Sec. 25.981 to address

both prevention of ignition sources in fuel tanks and reduction in the

time fuel tanks contain flammable vapors. The first proposal would

explicitly include a requirement for effectively precluding ignition

sources within the fuel tank systems of transport category airplanes.

The second proposal would require minimizing the formation of flammable

vapors in the fuel tanks.

Fuel Tank Ignition Source Proposal

The title of Sec. 25.981 would be changed from ``Fuel tank

temperature'' to ``Fuel tank ignition prevention.'' The FAA proposes to

retain the substance of existing paragraph (a), which requires the

applicant to determine the highest temperature that allows a safe

margin below the lowest expected auto ignition temperature of the fuel;

and the existing paragraph (b), which requires precluding the

temperature in the fuel tank from exceeding the temperature determined

under paragraph (a). These requirements are redesignated as (a)(1) and

(2) respectively.

Compliance with these paragraphs requires the determination of the

fuel flammability characteristics of the fuels approved for use. Fuels

approved for use on transport category airplanes have differing

flammability characteristics. The fuel with the lowest autoignition

temperature is JET A (kerosene), which has an autoignition temperature

of approximately 450 deg.F at sea level. The autoignition temperature

of JP-4 is approximately 470 deg.F at sea level. Under the same

atmospheric conditions the autoignition temperature of gasoline is

approximately 800 deg.F. The autoignition temperature of these fuels

increases at increasing altitudes (lower pressures). For the purposes

of this rule the lowest temperature at which autoignition can occur for

the most critical fuel approved for use should be determined. The FAA

intends that a temperature providing a safe margin is at least 50

deg.F below the lowest expected autoignition temperature of the fuel

throughout the altitude and temperature envelopes approved for the

airplane type for which approval is requested.

This proposal would also add a new paragraph (a)(3) to require that

a safety analysis be performed to demonstrate that the presence of an

ignition source in the fuel tank system could not result from any

single failure, from any single failure in combination with any latent

failure condition not shown to be extremely remote, or from any

combination of failures not shown to be extremely improbable.

These new requirements define three scenarios that must be

addressed in order to show compliance with the proposed paragraph

(a)(3). The first scenario is that any single failure, regardless of

the probability of occurrence of the failure, must not cause

[[Page 58655]]

an ignition source. The second scenario is that any single failure,

regardless of the probability occurrence, in combination with any

latent failure condition not shown to be at least extremely remote

(i.e., not shown to be extremely remote or extremely improbable), must

not cause an ignition source. The third scenario is that any

combination of failures not shown to be extremely improbable must not

cause an ignition source.

For the purpose of this proposed rule, ``extremely remote'' failure

conditions are those not anticipated to occur to each airplane during

its total life, but which may occur a few times when considering the

total operational life of all airplanes of the type. This definition is

consistent with that proposed by the Aviation Rulemaking Advisory

Committee (ARAC) for a revision to FAA AC 25.1309-1A and that currently

used by the Joint Aviation Authorities (JAA) in AMJ 25.1309.

``Extremely improbable'' failure conditions are those so unlikely that

they are not anticipated to occur during the entire operational life of

all airplanes of one type. This definition is consistent with the

definition provided in FAA AC 25.1309-1A and retained in the draft

revision to AC 25.1309-1A proposed by the ARAC.

The severity of the external environmental conditions that should

be considered when demonstrating compliance with this proposed rule are

those established by certification regulations and special conditions

(e.g., HIRF), regardless of the associated probability. The proposed

regulation would also require that the effects of manufacturing

variability, aging, wear, and likely damage be taken into account when

demonstrating compliance.

The proposed requirements are consistent with the general

powerplant installation failure analysis requirements of Sec. 25.901(c)

and the systems failure analysis requirements of Sec. 25.1309 as they

have been applied to powerplant installations. This proposal is needed

because the general requirements of Secs. 25.901 and 25.1309 have not

been consistently applied and documented when showing that ignition

sources are precluded from transport category airplane fuel tanks.

Compliance with the proposed revision to Sec. 25.981 would require

analysis of the airplane fuel tank system using analytical methods and

documentation currently used by the aviation industry in demonstrating

compliance with Secs. 25.901 and 25.1309. In order to eliminate any

ambiguity as to the necessary methods of compliance, the proposed rule

explicitly requires that the existence of latent failures be assumed

unless they are extremely remote, which is currently required under

Sec. 25.901, but not under Sec. 25.1309. The analysis should be

conducted assuming design deficiencies listed in the background section

of this notice, and any other failure modes identified within the fuel

tank system functional hazard assessment.

Based upon the evaluations required by paragraph (a), a new

requirement would be added to paragraph (b) to require that critical

design configuration control limitations, inspections, or other

procedures be established as necessary to prevent development of

ignition sources within the fuel tank system, and that they be included

in the Airworthiness Limitations section of the ICA required by

Sec. 25.1529. This requirement would be similar to that contained in

Sec. 25.571 for airplane structure. Appendix H to part 25 would also be

revised to add a requirement to provide any mandatory fuel tank system

inspections or maintenance actions in the limitations section of the

ICA.

Critical design configuration control limitations include any

information necessary to maintain those design features that have been

defined in the original type design as needed to preclude development

of ignition sources. This information is essential to ensure that

maintenance, repairs or alterations do not unintentionally violate the

integrity of the original fuel tank system type design. An example of a

critical design configuration control limitation for current designs

discussed previously would be maintaining wire separation between FQIS

wiring and other high power electrical circuits. The original design

approval holder must define a method of ensuring that this essential

information will be evident to those that may perform and approve such

repairs and alterations. Placards, decals or other visible means must

be placed in areas of the airplane where these actions may degrade the

integrity of the design configuration. In addition, this information

should be communicated by statements in appropriate manuals, such as

Wiring Diagram Manuals.

Flammability Proposal

The FAA agrees with the intent of the recommended regulatory text

recommended by the ARAC. However, due to the short timeframe that the

ARAC was provided to complete the tasking, sufficient detailed economic

evaluation was not completed to determine if practical means, such as

ground based inerting, were available to reduce the exposure below the

specific value of 7 percent of the operational time included in the

ARAC proposal. In addition the 7 percent level of flammability proposed

by the FTHWG does not minimize flammability on certain applications,

while in other applications, such as very short haul operations, it may

not be practical to achieve. Therefore, the FAA is proposing a more

objective regulation that is intended to minimize exposure to operation

with flammable conditions in the fuel tanks.

As discussed previously, the ARAC has submitted a recommendation to

the FAA that the FAA continue to evaluate means for minimizing the

development of flammable vapors within the fuel tanks. Development of a

definitive standard to address this recommendation will require a

significant research effort that will likely take some time to

complete. In the meantime, however, the FAA is aware that historically

certain design methods have been found acceptable that, when compared

to readily available alternative methods, increase the likelihood that

flammable vapors will develop in the fuel tanks. For example, in some

designs, including the Boeing 747, air conditioning packs have been

located immediately below a fuel tank without provisions to reduce

transfer of heat from the packs to the tank.

Therefore, in order to preclude the future use of such design

practices, this proposal would revise Sec. 25.981 to add a requirement

that fuel tank installations be designed to minimize the development of

flammable vapors in the fuel tanks. Alternatively, if an applicant

concludes that such minimization is not advantageous, it may propose

means to mitigate the effects of an ignition of fuel vapors in the fuel

tanks. For example, such means might include installation of fire

suppressing polyurethane foam or installation of an explosion

suppression system.

This proposal is not intended to prevent the development of

flammable vapors in fuel tanks because total prevention has currently

not been found to be feasible. Rather, it is intended as an interim

measure to preclude, in new designs, the use of design methods that

result in a relatively high likelihood that flammable vapors will

develop in fuel tanks when other practicable design methods are

available that can reduce the likelihood of such development. For

example, the proposal would not prohibit installation of fuel tanks in

the cargo compartment, placing heat exchangers in fuel tanks, or

locating a fuel tank in the center wing. The proposal would, however,

require that practical means, such as transferring

[[Page 58656]]

heat from the fuel tank (e.g., use of ventilation or cooling air), be

incorporated into the airplane design if heat sources were placed in or

near the fuel tanks that significantly increased the formation of

flammable fuel vapors in the tank, or if the tank is located in an area

of the airplane where little or no cooling occurs. The intent of the

proposal is to require that fuel tanks are not heated, and cool at a

rate equivalent to that of a wing tank in the transport airplane being

evaluated. This may require incorporating design features to increase

or provide ventilation means for fuel tanks located in the center wing

box, horizontal stabilizer, or auxiliary fuel tanks located in the

cargo compartment. At such time as the FAA has completed the necessary

research and identified an appropriate definitive standard to address

this issue, new rulemaking would be considered to revise the standard

proposed in this rulemaking.

Applicability of Proposed Part 25 Change

The proposed amendments to part 25 would apply to all transport

category airplane models for which an application for type

certification is made after the effective date of the rule, regardless

of passenger capacity or size. In addition, as currently required by

the provisions of Sec. 21.50, applicants for any future changes to

existing part 25 type certificated airplanes, including STCs, that

could introduce an ignition source in the fuel tank system would be

required to provide any necessary Instructions for Continued

Airworthiness, as required by Sec. 25.1529 and the proposed change to

the Airworthiness Limitations section, paragraph H25.4 of Appendix H.

In cases where it is determined that the existing ICA are adequate for

the continued airworthiness of the altered product, then it should be

noted on the STC, PMA supplement, or major alteration approval.

FAA Advisory Material

In addition to the amendments proposed in this notice, the FAA is

developing a proposed revision to AC 25.981-1A, ``Guidelines for

Substantiating Compliance With the Fuel Tank Temperature

Requirements.'' The proposed revision will include consideration of

failure conditions that could result in sources of ignition of vapors

within fuel tanks. The revised AC will provide guidance on how to

substantiate that ignition sources will not be present in airplane fuel

tank systems following failures or malfunctions of airplane components

or systems. This AC will also include guidance for developing any

limitations for the ICA that may be generated by the fuel tank system

safety assessment. Public comments concerning the proposed AC will be

requested by separate notice published in the Federal Register.

Future Regulatory Actions

The ARAC report discussed earlier does not recommend specific

actions to eliminate or significantly reduce the flammability of fuel

tanks in current production and the existing fleet of transport

airplanes. The report, however, recommends that the FAA continue to

investigate means to achieve a cost-effective reduction in flammability

exposure for these airplanes. The FAA has reviewed the report and

established research programs to support the further evaluation needed

to establish the practicality of methods for achieving reduced

flammability exposure for newly manufactured and the existing fleet of

transport airplanes. The FAA intends to initiate rulemaking to address

these airplanes if practical means are established.

Economic Evaluation, Regulatory Flexibility Determination,

International Trade Impact Assessment, and Unfunded Mandates

Assessment

Proposed changes to Federal regulations must undergo several

economic analyses. First, Executive Order 12866 directs that each

Federal agency shall propose or adopt a regulation only upon a reasoned

determination that the benefits of the intended regulation justify its

costs. Second, the Regulatory Flexibility Act of 1980 requires agencies

to analyze the economic impact of regulatory changes on small entities.

Third, the Office of Management and Budget directs agencies to assess

the effects of regulatory changes on international trade. And fourth,

the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4) requires

agencies to prepare a written assessment of the costs, benefits, and

other effects of proposed or final rules that include a Federal mandate

likely to result in the expenditure by State, local, or tribal

governments, in the aggregate, or by the private sector, of $100

million or more annually (adjusted for inflation). In conducting these

analyses, the FAA has determined that this proposed rulemaking: (1)

would generate benefits that justify its costs as required by Executive

Order 12866 and would be a ``significant regulatory action'' as defined

in DOT's Regulatory Policies and Procedures; (2) would have a

significant economic impact on a substantial number of small entities;

(3) would have minimal effects on international trade; and (4) would

not contain a significant intergovernmental or private sector mandate.

These analyses, available in the docket, are summarized as follows.

Affected Industries

Based on 1996 data, the proposal would affect 6,006 airplanes, of

which 5,700 airplanes are operated by 114 air carriers under part 121

service, 193 airplanes are operated by 7 carriers that operate under

both part 121 and part 135, 22 airplanes are operated by 10 carriers

under part 125 service, and 91 airplanes are operated by 23 carriers

operating U.S.-registered airplanes under part 129. At this time, the

FAA does not have information on airplanes operating under part 91 that

would be affected by the proposed rulemaking; however, the FAA believes

that very few airplanes operating under part 91 would be affected by

the proposal.

The proposed rule would also affect 12 manufacturers holding 35

type certificates (TCs) and 26 manufacturers and airlines holding 168

supplemental type certificates (STCs). The proposed rule would also

affect manufacturers of future, new part 25 type certificated airplane

models and holders of future, new part 25 supplemental type

certificates for new fuel tank systems. At this time, the FAA cannot

predict the number of new airplane models. Based on the past 10 years

average, the FAA anticipates that about 17 new fuel tank system STCs

would be granted annually. The FAA requests comments on these estimates

and requests that commenters provide clear supporting additional

information.

Benefits

In order to quantify the benefits from preventing future fuel tank

explosions, the FAA assumes that the potential U.S. fuel tank explosion

rate due to an unknown internal fuel tank ignition source is similar to

the worldwide fleet explosion rate over the past 10 years. On that

basis, the FAA estimates that if no preventative actions were to be

taken, between one and two (the expected value would be 1.25) fuel tank

explosions would be expected to occur during the next 10 years in U.S.

operations.

By way of illustrating the potential effectiveness of an enhanced

fuel tank system inspection program, on May 14, 1998, the FAA issued AD

T98-11-52 requiring the inspection of fuel boost pump wires in the

center wing tank of all Boeing 737's with more than 30,000

[[Page 58657]]

hours. Of the 599 airplanes inspected as of June 30, 1998, 273 wire

bundles had noticeable chafing to wire insulation, 33 had significant

(greater than 50 percent) insulation chafing, 8 had arcing on the cable

but not through the conduit, while 2 had arcing through the conduit

into the fuel tank.

In light of the findings from these inspections, the FAA believes

that better fuel tank system inspections would be a significant factor

in discovering potential fuel tank ignition sources. The FAA

anticipates that compliance with the proposal would prevent between 75

percent and 90 percent of the potential future fuel tank explosions

from unknown ignition sources.

Using a value of $2.7 million to prevent a fatality, a value of the

destroyed airplane of $20 million, an average of $30 million for an FAA

investigation of an explosion, and assuming the proposal would prevent

between 75 percent and 90 percent of these potential fuel tank

explosions from an unknown ignition source, the potential present value

of the expected benefits discounted over 10 years at 7 percent would be

between $260 million and $520 million.

In addition, the proposed part 25 change would reduce the length of

time that an explosive atmosphere would exist in the fuel tank during

certain operations for new part 25 type certificated airplanes and for

new fuel tank system STCs. At this time, the FAA cannot quantify these

potential benefits, but they are not expected to be considerable in the

immediate future. The FAA expects that these benefits would increase

over time as new part 25 type certificated airplanes replace the older

part 25 type certificated airplanes in the fleet.

Compliance Costs

The proposal consists of three parts. The first two are separate

but interrelated parts, each of which would impose costs on the

industry. The first is the proposed SFAR. The second is the proposed

operational rules changes from the recommendations following the SFAR.

The third part is the proposed part 25 change.

The compliance costs for the proposed SFAR would be due to the

requirement for the design approval holder to complete a comprehensive

fuel tank system design assessment and to provide recommendations for

the inspections and model-specific service instructions within one year

from the SFAR's effective date. The assessment may identify conditions

that would be addressed by specific service bulletins or unsafe

conditions that would result in FAA issuance of an airworthiness

directive (AD). However, those future costs would be the result of

compliance with the service bulletin or the AD and are not costs of

compliance with the proposed rulemaking. Those costs would be estimated

for each individual AD, when proposed. In addition, the compliance

costs do not include the compliance costs from an existing fuel tank

AD.

The compliance costs for the proposed operational rule changes

would be due to the requirement for the air carrier to incorporate

these recommendations into its fuel tank system inspection and

maintenance program within 18 months from the proposal's effective

date. These compliance costs do not include the costs to repair and

replace equipment and wiring that is found to need repair or

replacement during the inspection. Although these costs are likely to

be substantial, they are attributable to existing FAA regulations that

require such repairs and replacements be made to assure the airplane's

continued airworthiness.

The FAA anticipates that the proposed part 25 change would have a

minimal effect on the cost of future type certificated airplanes

because compliance with the proposed change would be done during the

design phase of the airplane model before any new airplanes would be

manufactured.

In addition, the FAA determines, after discussion with industry

representatives, that the proposed part 25 changes would have a minimal

impact on future fuel tank system STCs because current industry design

practices could be adapted to allow compliance with the proposed

requirement.

Costs of Fuel Tank System Design Assessments--New SFAR

The FAA has determined that 35 TCs and 68 fuel tank system STCs

(many of the 168 STCs duplicate other STCs) would need a fuel tank

system design assessment. Depending upon the complexity of the fuel

tank system and the number of tanks, the FAA has estimated that a fuel

tank system design assessment would take between 0.5 to 2 engineer

years for a TC holder and an average of 0.25 engineer years for an STC

holder. The FAA estimates that developing manual revisions and service

bulletins would take between 0.25 to 1 engineer years for a TC holder

and an average of 0.1 engineer years for an STC holder. In addition,

the FAA and the TC or STC holder would each spend between 1 day and 5

days to review, revise, and approve the assessment and the changes to

the manual.

Using a total engineer compensation rate (salary and fringe

benefits plus a mark-up for hours spent by management, legal, etc. on

the assessment) of $100 an hour, the FAA estimates that the one-time

fuel tank system design assessment would cost TC holders a total of

$9.5 million, it would cost STC holders a total of $4.9 million, and it

would cost the FAA about $220,000.

The FAA requests comments on the assumptions and the methodology

and also requests that commenters provide additional data.

Costs of Fuel Tank System Inspections--Operational Rule Changes

Methodology: The costs to air carriers of complying with the

operational requirements proposed for Parts 91, 121, 125, and 129 would

be the additional (incremental) labor hours and additional airplane

out-of-service time to perform the enhanced fuel tank system

maintenance and inspections. However, the costs of the fuel tank system

inspections that have been required by recent ADs are not included as a

cost of complying with the proposed operational amendments.

The FAA intends that any additional fuel tank system inspection and

maintenance actions resulting from the SFAR review would occur during

an airplane's regularly scheduled major maintenance checks. From a

safety standpoint, repeated entry increases the risk of damage to the

airplane. Thus, the proposal would not require air carriers to alter

their maintenance schedules, and the FAA anticipates that few or no

airplanes would be taken out of service solely to comply with the

proposal unless an immediate safety concern is identified. In that

case, corrective action would be mandated by an AD.

The FAA anticipates that the proposal would require additional time

out of service and man-hours to complete a fuel tank system inspection

and equipment and wiring testing.

The FAA-estimated number of additional hours (for both man-hours

and time out of service) to perform each of the various inspections is

derived primarily from the available service bulletins and from

discussions with airline maintenance engineers. For those turbojet

models that have not been the subject of a fuel tank system inspection

service bulletin, the FAA adopted the estimated hours from existing

service bulletins of similar types of turbojet models. Although there

have been no fuel tank system inspection service bulletins for

turboprops, the FAA

[[Page 58658]]

received information concerning the estimated fuel tank system

inspection time for a turboprop from commuter airline maintenance

personnel. Based on this information and an FAA analysis that turboprop

fuel tanks are smaller and have less equipment than turbojet fuel

tanks, the FAA estimates that a turboprop fuel tank system inspection

would take between one-third to one-half of the time it would take for

the turbojet fuel tank system inspections defined in available

bulletins.

The FAA requests comments on these estimates and that commenters

provide supporting data.

Estimated Compliance Costs: The following cost and hour estimates

are summaries of the Regulatory Evaluation of the proposal. The

detailed estimated compliance costs, including all assumptions and the

spreadsheet used for the calculations, are in that document, which is

available in the docket.

The incremental cost of complying with the operational proposals

would consist of the following four components: (1) the labor hours to

incorporate the recommendations into the inspections manual; (2) the

labor hours needed to perform the fuel tank system inspection; (3) the

cost of the additional downtime required to complete the inspection;

and (4) the increased documentation and reporting of the inspection and

subsequent findings.

The FAA estimates that it would take an average of 5 engineer days

to incorporate the recommendations into the inspections manual, for a

cost of about $4,000 per airplane model per operator, with a total cost

of about $1.16 million.

The FAA estimates that the increased number of labor hours per

airplane resulting from the enhanced fuel tank system inspection and

maintenance would range from 19 hours to 110 hours in the first three

years, and would decline to 9 hours to 60 hours beginning in the fourth

year. Using a total compensation rate (wages plus fringe benefits) of

$70 an hour for maintenance personnel, the FAA estimates that the

annual per airplane costs of compliance would range from $1,330 to

$7,700 in each of the first 3 years and from $630 to $4,200 in each

year thereafter.

The FAA estimates that the total annual inspection costs would be

about $21.1 million during the first year, increasing by 4.3 percent

per year from the projected increase in airline operations until the

fourth year, when it would decline to about $10.1 million increasing by

4.3 percent each year thereafter. The present value of the total

operational cost, discounted at 7 percent over 10 years, would be about

$100 million.

As noted earlier, equipment costs would not be attributed to the

proposal but rather to the existing FAA airworthiness requirements. For

example, inspecting fuel boost pump wiring may involve its disassembly

and then reinstallation. Regardless of the wiring's condition, the cost

of complying with the proposal would include reinstallation time.

However, if the inspection or testing revealed the need for new wiring,

the new wiring cost is not attributed to the proposal.

The proposal would increase out-of-service time because only a

limited number of maintenance employees can work inside of a fuel tank

at any point in time, and thereby would not allow air carriers the

flexibility to perform the fuel tank system inspections during

regularly scheduled major maintenance checks. Thus, the time to open

the tank, drain the fuel, vent the tank, and close the tank are not

costs attributed to the proposal because those activities are necessary

to complete a scheduled maintenance check. On that basis, the FAA

estimates that this annual increase in out-of-service time would be

between 11.5 hours and 32 hours per airplane for each of the first 3

years and then decline to 10 to 25 hours per airplane in each year

thereafter.

The economic cost of out-of-service time is lost net revenue, which

is computed using the Office of Management and Budget (OMB)

determination that the average annual risk-free productive rate of

return on capital is 7 percent of the average value of that airplane

model. Thus, out-of-service lost net revenue per fuel tank system

inspection ranges from $50 to $9,750 per airplane, depending upon the

airplane model. Assuming one major inspection per year, the total

annual out-of-service lost net revenue would be about $6.4 million

during the first year, increasing by 4.3 percent per year until the

fourth year when it would decline to about $2.95 million but increase

by 4.3 percent each year thereafter. The present value of this total

lost net revenue, discounted at 7 percent over 10 years, would be about

$35.6 million.

The FAA estimates that the increased annual documentation and

reporting time would be one hour of recordkeeping for every 8 hours of

labor time in the first three years, and one hour of recordkeeping for

every 10 hours of labor time in every year thereafter. Thus, the per

airplane annual documentation cost would be between $150 and $850 in

the first three years becoming $100 to $540 each year thereafter.

To estimate the total documentation cost, it is noted that there is

a voluntary industry program to inspect certain airplane model fuel

tanks and report the findings and corrective actions taken to the

manufacturer. The reporting costs of compliance associated with the

proposal would not include these airplanes. On that basis, the FAA

estimates that the present value of the total recordkeeping cost

discounted at 7 percent for 10 years would be about $17.4 million.

Costs of Future Fuel Tank System Design Changes--Revised Part 25

The FAA anticipates that these discounted costs would be minimal

for new type certificated airplanes because these design costs would be

incurred in the future by airplane models yet to be designed. After

consultation with industry, the FAA also anticipates that these

discounted costs would be minimal for future fuel tank system design

supplemental type certificates because the existing systems would

largely be in compliance. The FAA requests comments and supporting data

on these determinations.

Total Costs of Proposed SFAR and Proposed Operational Rules Changes

Thus, the FAA estimates that the present value of the total cost of

complying with the proposed SFAR and the proposed operational rules

changes discounted over 10 years at 7 percent would be about $170

million.

Benefit-Cost Comparison of the Proposed Part 25 Change

Although the FAA does not have quantified costs and benefits from

the proposed part 25 changes at this time, the FAA believes that the

future benefits would likely be greater than the future costs. The FAA

requests comments and additional data on this determination.

Benefit-Cost Comparison of the Proposed SFAR and the Proposed

Operational Rules Changes

In comparing the estimated benefits and costs, the FAA determines

that using the lowest expected benefit estimate, the expected present

value of the benefits ($260 million) would be about 50 percent greater

than the present value of the total compliance costs ($170 million).

Thus, the FAA concludes that the proposed SFAR and the proposed

operational rules changes would be cost-beneficial.

[[Page 58659]]

Regulatory Flexibility Determination

The Regulatory Flexibility Act of 1980 establishes ``as a principle

of regulatory issuance that agencies shall endeavor, consistent with

the objective of the rule and of applicable statutes, to fit regulatory

and informational requirements to the scale of the business,

organizations, and governmental jurisdictions subject to regulation.''

To achieve that principle, the Act requires agencies to solicit and

consider flexible regulatory proposals and to explain the rationale for

their actions. The Act covers a wide range of small entities, including

small businesses, not-for-profit organizations, and small governmental

jurisdictions.

Agencies must perform a review to determine whether a proposed or

final rule will have a significant economic impact on a substantial

number of small entities. If the determination finds that it will, the

agency must prepare a Regulatory Flexibility Analysis (RFA) as

described in the Act.

However, if an agency determines that a proposed or final rule is

not expected to have a significant economic impact on a substantial

number of small entities, section 605(b) of the 1980 Act provides that

the head of the agency may so certify, and an RFA is not required. The

certification must include a statement providing the factual basis for

this determination, and the reasoning should be clear. Recently, the

Office of Advocacy of the Small Business Administration (SBA) published

new guidance for Federal agencies in responding to the requirements of

the Regulatory Flexibility Act, as amended.

Application of that guidance to the proposed part 25 change would

only affect future airplane manufacturers; and currently all

manufacturers of part 25 type certificated airplanes are considered to

be large manufacturers. Although the proposed changes to part 25 would

also affect future fuel tank system STCs, industry sources indicate

that current industry designs would meet the proposed requirement.

Thus, the FAA certifies that the proposed part 25 change would not have

a significant economic impact on a substantial number of small airplane

manufacturing entities.

However, application of that guidance to the proposed SFAR and to

the proposed operational rule changes indicates that it would have a

significant economic impact on a substantial number of small air

carrier entities that have one to nineteen airplanes. Accordingly, a

complete preliminary regulatory flexibility analysis was conducted for

those two elements of the proposal and is summarized as follows.

1. Reasons why the FAA is considering the proposed rule. This

proposed action is being considered in order to prevent airplane

explosions and the resultant loss of life (as evidenced by TWA Flight

800). Existing fuel tank system inspection programs may not provide

comprehensive, systematic prevention and control of ignition sources in

airplane fuel tanks.

2. The objectives and legal basis for the proposal. The objective

of the proposal is to ensure the continuing airworthiness of airplanes

certificated with 30 or more passengers or with a payload of 7,500

pounds or more. The design approval holder [including type certificates

(TC) and supplemental type certificates (STC)] would be required to

perform a design fuel tank system assessment and provide

recommendations and instructions concerning fuel tank system

inspections and equipment and wiring testing to the operators of those

airplanes, as well as to create service bulletins and provide data to

the FAA to support any needed ADs. An operator working under part 91,

under part 121, under part 125, and all U.S.-registered airplanes used

in scheduled passenger carrying operations under part 129, would be

required to incorporate these recommendations or other approved

instructions into the inspection manual and to perform these

inspections and tests. The legal basis for the proposal is found in 49

U.S.C. 44901 et seq. As a matter of policy, the FAA must, as its

highest priority (49 U.S.C. 40101(d)), maintain and enhance safety and

security in air commerce.

3. All relevant federal rules that may duplicate, overlap, or

conflict with the proposal. The FAA is unaware of any federal rules

that would duplicate, overlap, or conflict with the proposal.

4. A description and an estimate of the number of small entities to

which the proposal would apply. The proposal would apply to the

operators of all airplanes certificated with 30 or more passengers or a

7,500 pound or more payload operated under part 91, part 121, part 125,

and all U.S.-registered airplanes operated under part 129. Standard

industrial classification (SIC) coding does not exactly coincide with

the subsets of operators who could be affected by the proposal.

Nevertheless, using data from the SBA, the distributions of employment

size and estimated receipts for all scheduled air transportation firms

(SIC Code 4512), given in Table 1 below, are representative of the

operators who would be affected by the proposal.

5. The projected reporting, recordkeeping, and other compliance

requirements of the proposal. The proposal would not impose any

incremental recordkeeping authority. Existing 14 CFR part 43, in part,

already prescribes the content, form, and disposition of maintenance,

preventive maintenance, rebuilding, and alteration records for any

aircraft having a U.S. airworthiness certificate or any foreign

registered aircraft used in common carriage under part 121. The FAA

recognizes, however, that the proposal would necessitate additional

inspection and testing work, and consequently would also require the

completion of the additional recordkeeping associated with that

additional work.

The FAA estimates that each 8 additional hours of actual inspection

and testing required under the proposal would require one additional

hour for reporting and recordkeeping (7.5 recordkeeping minutes per

inspection hour). This recordkeeping would be performed by the holder

of an FAA-approved repairman or maintenance certificate. The projected

recordkeeping and reporting costs of the proposal are included as part

of the overall costs computed in the evaluation and included below in

the Regulatory Flexibility Cost Analysis.

Table 1.

------------------------------------------------------------------------

Estimated

Operator Category (No. of employees) Number of receipts (in

firms $1,000)

------------------------------------------------------------------------

0-4..................................... 153 193,166

5-9..................................... 57 145,131

10-19................................... 56 198,105

20-99................................... 107 1,347,711

101-499................................. 74 3,137,624

500+.................................... 73 112,163,942

-------------------------------

Total............................... 520 117,185,679

------------------------------------------------------------------------

Table 2 categorizes the estimated number of operators by number of

airplanes that would be affected by the proposal and provides an

estimate of the total number of affected airplanes in that operator

category. Based on existing operator/airplane distributions, the FAA

estimates that 131 U.S. operators would be subject to the proposal.

(Note that this excludes the 19 non-U.S. owners of U.S.-registered

airplanes that would be affected by the proposal. It should also be

noted that Table 2 excludes Boeing 747 models, and, therefore,

operators who exclusively fly Boeing 747s.)

[[Page 58660]]

Table 2.

------------------------------------------------------------------------

No. of Total No. of

Operator category operators airplanes

------------------------------------------------------------------------

0-4..................................... 48 93

5-9..................................... 17 108

10-19................................... 22 271

20-29................................... 13 277

30-39................................... 4 145

40-49................................... 5 220

-------------------------------

Total 0-50.......................... 109 1,114

50+..................................... 22 4,594

-------------------------------

U.S. Total.......................... 131 5,708

Non-U.S................................. 23 62

-------------------------------

Total............................... 154 5,770

------------------------------------------------------------------------

6. Regulatory Flexibility Cost Analysis. The proposal would consist

of two actions affecting small business expenses. The first action, the

proposed SFAR, would require all design approval TC holders and fuel

tank system STC holders: (1) to complete a fuel tank system design

assessment and to generate future service bulletins and provide data to

the FAA; and (2) to provide operators with recommendations for fuel

tank system inspections, testing, and maintenance. The second action,

the proposed operational rules changes, would require that operators

incorporate these recommendations for an enhanced fuel tank system

inspection and equipment and wiring testing into the inspection and

maintenance manuals. This proposal would apply to both existing and

future production airplanes and to future TCs and STCs. This Regulatory

Flexibility Cost Analysis focuses on the costs to operators of existing

and future production airplanes, because almost 99 percent of the

estimated costs of the proposal would be incurred by operators of those

airplanes.

Table 3 summarizes the results for the total annualized compliance

costs for U.S. operators only and also provides the estimated cost per

operator and per airplane by each operator size category.

Table 3.

----------------------------------------------------------------------------------------------------------------

Per operator Per airplane

Operator category (No. of airplanes) Total costs cost cost

----------------------------------------------------------------------------------------------------------------

0-4............................................................. $293,000 $6,100 $3,150

5-9............................................................. 275,000 16,175 2,550

10-19........................................................... 1,123,000 51,050 4,150

20-29........................................................... 784,000 60,300 2,825

30-39........................................................... 234,000 58,500 1,600

40-49........................................................... 262,000 52,400 1,200

-----------------------------------------------

Total 0-4................................................... 2,971,000 27,250 2,675

50+............................................................. 17,820,000 810,000 3,775

-----------------------------------------------

Total....................................................... 20,791,000 158,700 3,650

----------------------------------------------------------------------------------------------------------------

7. Affordability Analysis. Although the FAA lacks financial data

for most of the smallest operators, if the average operating revenues,

calculated to be about $1.25 million for the category of 0 to 4

employees from Table 1, are compared to the average annualized

compliance costs from Table 3 (an admittedly crude method), it appears

that the average operator would pay no more than 0.5 percent of

operating revenues, based on an average annual risk-free return of 7

percent of the value of the airplane, to comply with the proposal. On

that basis, most small entities would be able to offset the incremental

compliance costs. Nevertheless, it is likely that there would be some

of the very small operators (those with 1 to 9 affected airplanes) that

may have difficulties in offsetting these incremental costs. However,

due to the unavailability of current financial data from the Department

of Transportation on these smallest operators, the FAA cannot more

definitively determine the potential impact on these smallest affected

operators. The FAA solicits comments on these costs and requests that

all comments be accompanied with clear supporting data.

8. Disproportionality analysis. The principle factors determining

the compliance cost for an operator would be the type of airplane model

in the operator's fleet and the number of airplanes that would be

affected by the proposal. As noted in the compliance cost section, the

cost to inspect the fuel tank system of larger transport category

airplane models would be 3 to 4 times more than the cost for a small

transport category turboprop. Consequently, as seen in Table 3, the

average per airplane compliance cost for operators with more than 50

airplanes is generally higher than the average cost per airplane for

operators with fewer than 50 airplanes. This is due to the predominance

of turboprops in the 30-50 airplane fleets, which would have the lowest

compliance costs. However the per airplane cost for operators with 1 to

29 airplanes is higher than for the 30 to 50 airplane operators. Many

of the smallest operators with fewer airplanes are cargo

[[Page 58661]]

operators utilizing larger and older turbojets, and they have fewer

airplanes available to average the fixed costs associated with

compliance with the proposal. Nevertheless, in general, the average

compliance cost per airplane is relatively consistent for operators

with fewer than 50 affected airplanes. Further, the compliance cost

relative to these airplanes operating revenues would be relatively

small. As a result, the FAA does not believe that small entities, as a

group, would be disadvantaged relative to large air carriers due solely

to the slight disproportionate cost effects from compliance with the

proposal.

9. Competitiveness Analysis. The proposal would likely impose

significant costs on some of the smallest air carriers (those with 1 to

19 airplanes) and, as a consequence, may affect the relative position

of these carriers in their markets. However, most of these smallest air

carriers operate in ``niche'' markets in which the competition that

occurs arises from other small operators using largely similar

equipment and often competing on the basis of service rather than on

the basis of price. In such markets, the number of competitors is very

limited. For example, Atlas Air specializes in supplying international

air cargo by using large all-cargo airplanes to carry bulky cargo, like

oil rig equipment. Similarly, Northern Air Cargo specializes in mail

and air cargo to rural Alaska.

The FAA believes that most of the markets served by these smallest

air carriers are low-volume niche markets that larger air carriers have

in many cases abandoned, because the larger air carriers' fleets have

been designed for high-volume markets. Further, larger air carriers

would not be interested in servicing most of these markets because they

cannot compete on a cost basis. Thus, these smallest operators would be

able to avoid direct competition with larger air carriers. As a result,

to the extent that there would be adverse competitiveness effects, they

would likely be minimal and they would occur with other similar-sized

(1 to 19) air carriers. On that basis, the FAA concludes that small air

carriers would not lose market share to larger air carriers.

The proposal would not impose significant compliance costs on a

substantial number of small operators that have 20 or more airplanes

that would be affected by the proposal. These operators include large

regionals, medium regionals, commuter airlines, and air cargo carriers.

To some extent, these operators avoid direct competition with major

carriers. However, in those markets where there is competition between

the small entities and the larger air carriers, the proposal would have

minimal competitive impact, because the per airplane compliance cost

for a given airplane model would be roughly the same for a large and a

small operator.

10. Business Closure Analysis. The FAA is unable to determine with

certainty the extent to which small entities that would be

significantly affected by the proposal would have to close their

operations. Many of the very small operations (1 to 4 airplanes)

operate very close to the margin, as evidenced by the constant exit

from and entry into air carrier service of these types of air carriers.

Consequently, in the absence of financial data, it is difficult to

determine the extent to which the proposal would make the difference in

an entity's remaining in business.

11. Description of Alternatives. In the general course of

promulgating the proposed rule, the FAA has considered four approaches.

The three alternatives to the proposed rule are described below. In

formulating the alternatives, the FAA focused on its responsibility for

aviation safety and its particular obligation under 49 U.S.C. 44717 to

ensure the continuing airworthiness of airplanes. The three primary

alternatives to the proposal considered by the FAA varied with respect

to the number of airplanes to be included in the proposal. The proposed

rule would limit the potential impact on airplanes most likely to be

used by small entities, while meeting the Agency's safety

responsibility.

Alternative 1: Require all airplanes in commercial service with

more than 10 seats to be covered by the proposal.

Alternative 1 would require all airplanes operating under part 91,

121, 125, and 129 to comply with the proposal. This would also include

operators supplying on-demand service under part 135. The FAA estimates

that about 45 additional airplane models, about 2,360 additional

airplanes, and about 550 additional operators would be covered by this

proposed alternative. The airplane operation is not the principal

business for many of these additional operators. In estimating these

potential compliance costs, the FAA assumes that, due to their small

fuel tanks and relative straightforward fuel systems, these airplanes

would need one-half of the time reported for the smallest part 25

turboprop to complete the fuel tank system design assessment. In

addition, the FAA assumes that it would also take one-quarter of the

time reported for the smallest part 25 turboprop to complete the

enhanced fuel tank system inspection and maintenance and wiring

testing. Further, the FAA assumes that the out-of-service time would be

one-half of the labor time to complete the inspection and testing.

However, there would be no out-of-service time for part 135 on-demand

airplanes because those operators would normally schedule maintenance

when there was no activity. For the other operators, the FAA estimates

the value of the average airplane would be about $750,000.

The FAA estimates that the total additional compliance costs of

including these operators (including the fuel tank system design

assessment cost) would be about $7.4 million in the first-year,

becoming about $1.1 million in the fourth year. The total compliance

cost, discounted over 10 years at 7 percent, would be about $17.1

million. The annualized cost, discounted over 10 years at 7 percent,

would be about $2.4 million.

This proposed alternative would not significantly increase the

expected quantitative benefits because there have been no in-flight

fuel tank explosions of these airplanes. In light of the absence of a

fuel tank explosion accident history, the FAA does not believe at this

time that the increased cost from including these smaller airplanes

would be met with a commensurate level of benefits.

The FAA requests comments on these estimates and requests

commenters to provide supporting data for the comments.

Alternative 2: Require all airplanes in commercial service with 30

or more seats (the proposed rule), plus all airplanes with 10 or more

seats in scheduled commercial service, to be covered by the proposal.

Alternative 2 would add the requirement for all airplanes with 10

or more seats in scheduled commercial service operating under part 91,

part 121, part 125, and part 129 to comply with the proposal. The FAA

estimates that 30 additional airplane models, 724 additional airplanes,

and about 84 additional operators would be covered by this proposed

alternative. However, 35 of the 84 additional operators would already

have airplanes that would be covered by the proposal. In estimating

these potential compliance costs, the FAA makes the same assumptions

that were described under Alternative 1.

On that basis, the FAA estimates that the additional compliance

costs of including these operators (including the fuel tank system

design assessment cost) would be about $2.7 million in the first-year

and about $340,000 in the fourth

[[Page 58662]]

year. The total compliance cost, discounted over 10 years at 7 percent,

would be about $5.7 million. The annualized cost, discounted over 10

years at 7 percent, would be about $806,000. However, as also described

under Alternative 1, this proposed alternative would not significantly

increase the expected quantitative benefits because there have been no

in-flight fuel tank explosions of these airplanes.

The FAA requests comments on these estimates and requests

commenters to provide supporting data for the comments.

Alternative 3: Require that only turbojet airplanes in commercial

service be covered by the proposal.

This alternative would allow 1,034 turboprop airplanes certificated

under part 25 to be exempt from the proposal's requirements. By doing

so, it would reduce the first year cost of compliance to all of these

exempted airplanes by about $1.8 million, becoming about $545,000 in

the fourth year. The total compliance cost savings, discounted over 10

years at 7 percent, would be about $8.3 million. The total annualized

cost savings, discounted over 10 years at 7 percent, would be about

$1.2 million.

Although there have been no in-flight fuel tank explosions

associated with these part 25 turboprop airplane models, the FAA

believes that the underlying fuel tank system risk is similar to those

of the larger turbojets. On that basis, as the FAA's estimated overall

benefits are larger than its estimated overall costs, by extrapolation,

removing 20 percent of the population at risk from the proposed rule

would remove 20 percent of both the benefits and costs. As the benefits

are estimated to be greater than the costs, the result would be a

reduction in the net dollar benefits and higher safety risk. Finally,

these airplanes are part 25 certificated and the FAA considers that the

same level of safety should be applied to all part 25 certificated

airplanes. Thus, as a result of performing the regulatory flexibility

analysis and addressing the concerns of the SBA, the FAA believes that,

in comparison to the two higher cost alternatives and the one lower

cost alternative evaluated by the FAA, the proposal would provide the

necessary level of safety in the most cost-effective manner.

12. Special Considerations. As seen in Table 3, on a proportional

basis the proposal would have a slightly greater impact on larger air

carriers. The per airplane annualized cost for a large operator with 50

or more airplanes would be $3,775, where it would be about $2,675 for a

smaller operator. However, this difference is relatively small, and the

FAA concludes that the proposal would not alter the competitiveness of

small air carriers relative to larger air carriers.

13. Conclusion. For a small operator with an airplane worth $5

million, an annualized cost of $2,675 would be equal to about three

days of lost net revenue, based on an average annual risk-free

productive rate of return on capital of 7 percent. However, the FAA

also considers that even for small operators of these affected

airplanes, the safety benefits would be greater than the compliance

costs. The FAA requests comments on this analysis and requests

commenters to supply supporting data for the comments.

International Trade Impact Assessment

Consistent with the Administration's belief in the general

superiority, desirability, and efficacy of free trade, it is the policy

of the Administrator to remove or diminish, to the extent feasible,

barriers to international trade, including both barriers affecting the

export of American goods and services to foreign countries and those

affecting the import of foreign goods and services into the United

States.

In accordance with that policy, the FAA is committed to develop as

much as possible its aviation standards and practices in harmony with

its trading partners. Significant cost savings can result from this,

both to American companies doing business in foreign markets, and

foreign companies doing business in the United States.

This proposed rule would have little or no impact on international

trade. The proposed part 25 change would equally affect all future part

25 airplanes, wherever manufactured, that would be registered in the

United States. Although the proposed operational rules changes would

affect only U.S. registered airplanes, the net effect is expected to be

small and the European Joint Aviation Authorities may consider similar

regulations.

Unfunded Mandates Assessment

Title II of the Unfunded Mandates Reform Act of 1995 (the Act),

enacted as Public Law 104-4 on March 22, 1995, requires each Federal

agency, to the extent permitted by law, to prepare a written assessment

of the effects of any Federal mandate in a proposed or final agency

rule that may result in the expenditure by State, local, and tribal

governments, in the aggregate, or by the private sector, of $100

million or more (adjusted annually for inflation) in any one year.

Section 204(a) of the Act, 2 U.S.C. 1534(a), requires the Federal

agency to develop an effective process to permit timely input by

elected officers (or their designees) of State, local, and tribal

governments on a proposed ``significant intergovernmental mandate.'' A

``significant intergovernmental mandate'' under the Act is any

provision in a Federal agency regulation that will impose an

enforceable duty upon State, local, and tribal governments, in the

aggregate, of $100 million (adjusted annually for inflation) in any one

year. Section 203 of the Act, 2 U.S.C. 1533, which supplements section

204(a), provides that before establishing any regulatory requirements

that might significantly or uniquely affect small governments, the

agency shall have developed a plan that, among other things, provides

for notice to potentially affected small governments, if any, and for a

meaningful and timely opportunity to provide input in the development

of regulatory proposals.

The FAA determines that this proposed rule would not contain a

significant intergovernmental or private sector mandate as defined by

the Act.

Federalism Implications

The regulations proposed herein will not have substantial direct

effects on the States, or on the relationship between the national

government and the States, or on the distribution of power and

responsibility among the various levels of the government. Therefore,

in accordance with Executive Order 12612, it is determined that this

proposed rule would not have significant federalism implications to

warrant the preparation of a Federalism Assessment.

International Civil Aviation Organization (ICAO) and Joint Aviation

Regulations

In keeping with U.S. obligations under the Convention on

International Civil Aviation, it is FAA policy to comply with ICAO

Standards and Recommended Practices to the maximum extent practicable.

The FAA has determined that this proposed rule would not conflict with

any international agreement of the United States.

Paperwork Reduction Act

There are no new requirements for information collection associated

with this proposed rule that would require approval from the Office of

Management and Budget pursuant to the Paperwork Reduction Act of 1995

(44 U.S.C. 3507(d)).

[[Page 58663]]

Regulations Affecting Intrastate Aviation in Alaska

Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat.

3213) requires the Administrator, when modifying regulations in Title

14 of the CFR in a manner affecting intrastate aviation in Alaska, to

consider the extent to which Alaska is not served by transportation

modes other than aviation, and to establish such regulatory

distinctions as he or she considers appropriate. Because this proposed

rule would apply to the operation of certain transport category

airplanes under parts 91, 121, 125, and 129 of Title 14, it could, if

adopted, affect intrastate aviation in Alaska. The FAA therefore

specifically requests comments on whether there is justification for

applying the proposed rule differently to intrastate operations in

Alaska.

List of Subjects

14 CFR Parts 21, 25, 91, 125 and 129

Aircraft, Aviation safety, Reporting and recordkeeping

requirements.

14 CFR Part 121

Aircraft, Aviation safety, Reporting and recordkeeping

requirements, Safety, Transportation.

The Proposed Amendment

In consideration of the foregoing, the Federal Aviation

Administration proposes to amend parts 21, 25, 91, 121, 125, and 129 of

Title 14, Code of Federal Regulations, as follows:

PART 21--CERTIFICATION PROCEDURES FOR PRODUCTS AND PARTS

1. The authority citation for part 21 continues to read as follows:

Authority: 42 U.S.C. 7572; 40105; 40113; 44701-44702, 44707.

44709, 44711, 44713, 44715, 45303.

2. In part 21, add SFAR No. XX to read as follows:

Special Federal Aviation Regulations

* * * * *

SFAR No. XX--Fuel Tank System Fault Tolerance Evaluation

Requirements

1. Applicability. This SFAR applies to the holders of type

certificates, and supplemental type certificates affecting the

airplane fuel tank system, for turbine-powered transport category

airplanes, provided the type certificate was issued after January 1,

1958, and the airplane has a maximum type certificated passenger

capacity of 30 or more, or a maximum type certificated payload

capacity of 7500 pounds or more. This SFAR also applies to

applicants for type certificates, amendments to a type certificate,

and supplemental type certificates affecting the fuel tank systems

for those airplanes identified above, if the application was filed

before the effective date of this SFAR and the certificate was not

issued before the effective date of this SFAR.

2. Compliance: No later than [12 months after the effective date

of the final rule], or within 12 months after the issuance of a

certificate for which application was filed before [effective date

of the final rule], whichever is later, each type certificate

holder, or supplemental type certificate holder of a modification

affecting the airplane fuel tank system, must accomplish the

following:

(a) Conduct a safety review of the airplane fuel tank system to

determine that the design meets the requirements of Secs. 25.901 and

25.981(a) and (b) of this chapter. If the current design does not

meet these requirements, develop all design changes necessary to the

fuel tank system to meet these requirements.

(b) Develop all maintenance and inspection instructions

necessary to maintain the design features required to preclude the

existence or development of an ignition source within the fuel tank

system of the airplane.

(c) Submit a report for approval of the Administrator that:

(1) Provides substantiation that the airplane fuel tank system

design, including all necessary design changes, meets the

requirements of Secs. 25.901 and 25.981(a) and (b) of this chapter;

and

(2) Contains all maintenance and inspection instructions

necessary to maintain the design features required to preclude the

existence or development of an ignition source within the fuel tank

system throughout the full operational life of the airplane.

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

3. The authority citation for part 25 continues to read:

Authority: 49 U.S.C. 106(g), 40113, 44701-44702, and 44704.

4. Section 25.981 is revised to read as follows:

Sec. 25.981 Fuel tank ignition prevention.

(a) No ignition source may be present at each point in the fuel

tank or fuel tank system where catastrophic failure could occur due to

ignition of fuel or vapors. This must be shown by:

(1) Determining the highest temperature allowing a safe margin

below the lowest expected autoignition temperature of the fuel in the

fuel tanks.

(2) Demonstrating that no temperature at each place inside each

fuel tank where fuel ignition is possible will exceed the temperature

determined under paragraph (a)(1) of this section. This must be

verified under all probable operating, failure and malfunction

conditions of each component whose operation, failure or malfunction

could increase the temperature inside the tank.

(3) Demonstrating that an ignition source could not result from

each single failure, from each single failure in combination with each

latent failure condition not shown to be extremely remote, and from all

combinations of failures not shown to be extremely improbable. The

effects of manufacturing variability, aging, wear, corrosion, and

likely damage must be considered.

(b) Based on the evaluations required by this section, critical

design configuration control limitations, inspections or other

procedures must be established as necessary to prevent development of

ignition sources within the fuel tank system and must be included in

the Airworthiness Limitations section of the ICA required by

Sec. 25.1529. Placards, decals or other visible means must be placed in

areas of the airplane where maintenance, repairs or alterations may

violate the critical design configuration limitations.

(c) The fuel tank installation must include--

(1) Means to minimize the development of flammable vapors in the

fuel tanks; or

(2) Means to mitigate the effects of an ignition of fuel vapors

within fuel tanks such that no damage caused by an ignition will

prevent continued safe flight and landing.

5. Paragraph H25.4 of Appendix H is revised to read as follows:

Appendix H To Part 25--Instructions for Continued Airworthiness

H25.4 Airworthiness Limitations section.

(a) The Instructions for Continued Airworthiness must contain a

section titled Airworthiness Limitations that is segregated and

clearly distinguishable from the rest of the document. This section

must set forth--

(1) Each mandatory replacement time, structural inspection

interval, and related structural inspection procedures approved

under Sec. 25.571; and

(2) each mandatory replacement time, inspection interval,

related inspection procedure, and all critical design configuration

control limitations approved under Sec. 25.981 for the fuel tank

system.

(b) If the Instructions for Continued Airworthiness consist of

multiple documents, the section required by this paragraph must be

included in the principle manual. This section must contain a

legible statement in a prominent location that reads: ``The

Airworthiness Limitations section is FAA-approved and specifies

maintenance required under Secs. 43.16 and 91.403 of the Federal

Aviation Regulations, unless an alternative program has been FAA

approved.''

[[Page 58664]]

PART 91--GENERAL OPERATING AND FLIGHT RULES

6. The authority citation for part 91 continues to read as follows:

Authority: 49 U.S.C. 1301(7), 1303, 1344, 1348, 1352 through

1355, 1401, 1421 through 1431, 1471, 1472, 1502, 1510, 1522, and

2121 through 2125; Articles 12, 29, 31, and 32(a) of the Convention

on International Civil Aviation (61 Stat. 1180); 42 U.S.C. 4321 et.

seq.; E.O. 11514; 49 U.S.C. 106(g) (Revised Pub. L. 97-449, January

21, 1983).

7. By adding a new Sec. 91.410 to read as follows:

Sec. 91.410 Fuel tank system maintenance and inspection instructions.

After [18 months after the effective date of the final rule], no

person may operate a turbine-powered transport category airplane with a

type certificate issued after January 1, 1958, and a maximum type

certificated passenger capacity of 30 or more, or a maximum type

certificated payload capacity of 7,500 pounds or more, unless

instructions for maintenance and inspection of the fuel tank system are

incorporated into its inspection program. Those instructions must be

approved by the Administrator. Thereafter, the approved instructions

can be revised only with the approval of the Administrator.

PART 121--OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL

OPERATIONS

8. The authority citation for part 121 continues to read as

follows:

Authority: 49 U.S.C. 106(g), 40113, 40119, 44101, 44701-44702,

44705, 44709-44711, 44713, 44716-44717, 44722, 44901, 44903-44904,

44912, 46105.

9. By adding a new Sec. 121.370 to read as follows:

Sec. 121.370 Fuel tank system maintenance and inspection instructions.

After [18 months after the effective date of the final rule], no

certificate holder may operate a turbine-powered transport category

airplane with a type certificate issued after January 1, 1958, and a

maximum type certificated passenger capacity of 30 or more, or a

maximum type certificated payload capacity of 7500 pounds or more,

unless instructions for maintenance and inspection of the fuel tank

system are incorporated in its maintenance program. Those instructions

must be approved by the Administrator. Thereafter, the approved

instructions can be revised only with the approval of the

Administrator.

PART 125--CERTIFICATION AND OPERATIONS: AIRPLANES HAVING A SEATING

CAPACITY OF 20 OR MORE PASSENGERS OR A MAXIMUM PAYLOAD CAPACITY OF

6,000 POUNDS OR MORE

10. The authority citation for part 125 continues to read as

follows:

Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44705, 44710-

44711, 44713, 44716-44717, 44722.

11. By adding a new Sec. 125.248 to read as follows:

Sec. 125.248 Fuel tank system maintenance and inspection instructions.

After [18 months after the effective date of the final rule], no

certificate holder may operate a turbine-powered transport category

airplane with a type certificate issued after January 1, 1958, and a

maximum type certificated passenger capacity of 30 or more, or a

maximum type certificated payload capacity of 7500 pounds or more

unless instructions for maintenance and inspection of the fuel tank

system are incorporated in its inspection program. Those instructions

must be approved by the Administrator. Thereafter, the approved

instructions can be revised only with the approval of the

Administrator.

PART 129--OPERATIONS: FOREIGN AIR CARRIERS AND FOREIGN OPERATORS OF

U.S.-REGISTERED AIRPLANE ENGAGED IN COMMON CARRIAGE

12. The authority citation for part 129 continues to read:

Authority: 49 U.S.C. 106(g), 40104-40105, 40113, 40119, 44701-

44702, 44712, 44716-44717, 44722, 44901-44904, 44906.

13. By amending Sec. 129.14 by adding a new paragraph (c) to read

as follows:

Sec. 129.14 Maintenance program and minimum equipment list

requirements for U.S.-registered airplanes.

* * * * *

(c) For turbine-powered transport category airplanes with a type

certificate issued after January 1, 1958, and a maximum type

certificated passenger capacity of 30 or more, or a maximum type

certificated payload capacity of 7500 pounds or more, no later than [18

months after the effective date of the final rule], the program

required by paragraph (a) of this section must include instructions for

maintenance and inspection of the fuel tank systems. Those instructions

must be approved by the Administrator. Thereafter the approved

instructions can be revised only with the approval of the

Administrator.

Issued in Washington, D.C., on October 26, 1999.

Elizabeth Erickson,

Director, Aircraft Certification Service.

[FR Doc. 99-28348 Filed 10-28-99; 8:45 am]

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