Airworthiness Directives; Boeing Model 727 Series Airplanes Modified in Accordance With Supplemental Type Certificate SA1368SO, SA1797SO, or SA1798SO

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-233-AD]

RIN 2120-AA64

Airworthiness Directives; Boeing Model 727 Series Airplanes

Modified in Accordance With Supplemental Type Certificate SA1368SO,

SA1797SO, or SA1798SO

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness

directive (AD) that is applicable to certain Boeing Model 727 series

airplanes that have been converted from a passenger to a cargo-carrying

(``freighter'') configuration. This proposal would require, among other

actions, installation of a fail-safe hinge, redesigned main deck cargo

door warning and power control systems, and 9g cargo barrier. This

proposal is prompted by the FAA's determination that the main deck

cargo door hinge is not fail-safe; that certain main deck cargo door

control systems do not provide an adequate level of safety; and that

the main deck cargo barrier is not structurally adequate during an

emergency landing. The actions specified by the proposed AD are

intended to prevent structural failure of the main deck cargo door

hinge or failure of the cargo door system, which could result in the

loss or opening of the cargo door while the airplane is in flight,

rapid decompression, and structural damage to the airplane; and to

prevent failure of the main deck cargo barrier during an emergency

landing, which could injure occupants.

DATES: Comments must be received by December 27. 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-114,

Attention: Rules Docket No. 97-NM-233-AD, 1601 Lind Avenue SW., Renton,

Washington 98055-4056. Comments may be inspected at this location by

appointment only between the hours of 9 a.m. and 3 p.m., Monday through

Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Paul Sconyers, Associate Manager,

Airframe and Propulsion Branch, ACE-117A, FAA, Small Airplane

Directorate, Atlanta Aircraft Certification Office, One Crown Center,

1895 Phoenix Boulevard, Suite 450, Atlanta, Georgia 30349; telephone

(770) 703-6076, fax (770) 703-6097.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the

proposed rule by submitting such written data, views, or arguments as

they may desire. Communications shall identify the Rules Docket Number

and be submitted in triplicate to the address specified above. All

communications received on or before the closing date for comments,

specified above, will be considered before taking action on the

proposed rule. The proposals contained in this notice may be changed in

light of the comments received.

Comments are specifically invited on the overall regulatory,

economic, environmental, and energy aspects of the proposed rule. All

comments submitted will be available, both before and after the closing

date for comments, in the Rules Docket for examination by interested

persons. A report summarizing each FAA-public contact concerned with

the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must submit a self-addressed,

stamped postcard on which the following statement is made: ``Comments

to Docket Number 97-NM-233-AD.'' The postcard will be date stamped and

returned to the commenter.

Availability of NPRMs

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

to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules

Docket No. 97-NM-233-AD, 1601 Lind Avenue, SW, Renton, Washington

98055-4056.

Discussion

Supplemental Type Certificates (STC) SA1797SO and SA1368SO (held by

Aeronautical Engineers, Inc.) specify a design for a main deck cargo

door, associated cargo door cutout, and door systems. STC SA1798SO

(held by Aeronautical Engineers, Inc.) specifies a design for a Class

``E'' cargo interior with a cargo barrier. As discussed in notice of

proposed rulemaking (NPRM), Rules Docket No. 97-NM-79-AD [the final

rule, AD 98-26-19, amendment 39-10962, was published in the Federal

Register on January 12, 1999 (64 FR 2016)], which is applicable to

certain Boeing Model 727 series airplanes that have been converted from

a passenger to a cargo-carrying (``freighter'') configuration, the FAA

has conducted a design review of Boeing Model 727 series airplanes

modified in accordance with STC's SA1797SO and SA1798SO and has

identified several potential unsafe conditions. [Results of this design

review are contained in ``FAA Freighter Conversion STC Review, Report

Number 3, dated January 27, 1997,'' hereinafter referred to as ``the

Design Review Report,'' which is included in the Rules Docket for this

NPRM.] This NPRM proposes corrective action for three of those

potential unsafe conditions that relate to the following three areas:

Main deck cargo door hinge, main deck cargo door systems, and main deck

cargo barrier.

Main Deck Cargo Door Hinge

In order to avoid catastrophic structural failure, it has been a

typical industry approach to design outward opening cargo doors and

their attaching structure to be fail-safe (i.e., designed so that if a

single structural element fails, other structural elements are able to

carry resulting loads). Another potential design approach is safe-life,

where the critical structure is shown by analyses and/or tests to be

capable of withstanding the repeated loads of variable magnitude

expected in service for a specific service life. Safe-life is usually

not used on critical structure because it is difficult to account for

manufacturing or in-service accidental damage. For this reason, plus

the fact that none of the STC holders have provided data in support of

this approach, the safe-life approach will not be discussed further

regarding the design and construction of the main deck cargo door

hinge.

Structural elements such as the main deck cargo door hinge are

subject to severe in-service operating conditions that could result in

corrosion, binding, or seizure of the hinge. These

[[Page 61548]]

conditions, in addition to the normal operational loads, can lead to

early and unpredictable fatigue cracking. If a main deck cargo door

hinge is not a fail-safe design, a fatigue crack could initiate and

propagate longitudinally undetected, which could lead to a complete

hinge failure. A possible consequence of this undetected failure is the

opening of the main deck cargo door while the airplane is in flight.

Service experience indicates that the opening of a cargo door while the

airplane is in flight can be extremely hazardous in a variety of ways

including possible loss of flight control, severe structural damage, or

rapid decompression, any of which, could lead to loss of the airplane.

The design of the main deck cargo door hinge must be in compliance

with Civil Air Regulations (CAR) part 4b, including CAR part 4b.270,

which requires, in part, that catastrophic failure or excessive

structural deformation, which could adversely affect the flight

characteristics of the airplane, is not probable after fatigue failure

or obvious partial failure of a single principal structural element.

One common feature of a fail-safe hinge design is a division of the

hinge into multiple segments such that, following failure of any one

segment, the remaining segments would support the redistributed load.

The main deck cargo door installed in accordance with STC's

SA1797SO and SA1368SO is supported by latches along the bottom of the

door and a two-segment hinge along the top. This two-segment hinge is

considered a critical structural element for these STC's. A crack that

initiates and propagates longitudinally along either segment of the

hinge will eventually result in failure of the entire hinge, because

the remaining segment of the hinge is unable to support the

redistributed loads. Failure of the entire hinge can result in the

opening of the main deck cargo door while the airplane is in flight.

As discussed in the Design Review Report, an inspection of one

Boeing Model 727 series airplane modified in accordance with STC's

SA1797SO and SA1798SO revealed a number of fasteners with both short

edge margins and short spacing in the cargo door cutout external

doublers. Some edge margins were as small as one fastener diameter.

Fasteners that are placed too close to the edge of a structural member

or spaced too close to an adjacent fastener can result in inadequate

joint strength and stress concentrations, which may result in fatigue

cracking of the skin. If such defects were to exist in the structure of

the door or the fuselage to which the main deck cargo door hinge is

attached, the attachment of the hinge could fail, and consequently

cause the door to open while the airplane is in flight.

Since unsafe conditions have been identified that are likely to

exist or develop on other products of this same type design, this

proposed AD would require, within 250 flight cycles after the effective

date of the AD, a one-time detailed visual inspection of the external

surface of the main deck cargo door hinge (both fuselage and door side

hinge elements) to detect cracks, and repair, if necessary.

Accomplishment of this inspection will ensure that the subject

airplanes are not in immediate risk of hinge failure.

In addition, the proposed AD would require a detailed visual

inspection of the mating surfaces of both the hinge and the door skin

and external fuselage doubler underlying the hinge to detect cracks or

other discrepancies (e.g., double or closely drilled holes, corrosion,

chips, scratches, or gouges). The proposed AD also would require

installation of a main deck cargo door hinge that complies with the

applicable requirements of CAR part 4b, including fail-safe

requirements. Accomplishment of this detailed visual inspection will

ensure the integrity of the door and fuselage structure to which the

hinge is attached. The proposed compliance time for this inspection and

installation is within 36 months or 4,000 flight cycles after the

effective date of this AD, whichever occurs first. The compliance time

is based on the FAA's assessment of the reasonable amount of time to

redesign, manufacture, and install a fail-safe hinge. This time is in

consideration of the 18-month time period estimated by the Boeing 727

industry working group, which includes operators, affected STC holders,

and engineering organizations, to develop FAA-approved redesigns. These

actions would be required to be accomplished in accordance with a

method approved by the FAA.

Main Deck Cargo Door Systems

In early 1989, two transport airplane accidents were attributed to

cargo doors coming open during flight. The first accident involved a

Boeing 747 series airplane in which the cargo door separated from the

airplane, and damaged the fuselage structure, engines, and passenger

cabin. The second accident involved a McDonnell Douglas DC-9 series

airplane in which the cargo door opened but did not separate from its

hinge. The open door disturbed the airflow over the empennage, which

resulted in loss of flight control and consequent loss of the airplane.

Although cargo doors have opened occasionally without mishap during

takeoff, these two accidents serve to highlight the extreme potential

dangers associated with the opening of a cargo door while the airplane

is in flight.

As a result of these cargo door opening accidents, the Air

Transport Association (ATA) of America formed a task force, including

representatives of the FAA, to review the design, manufacture,

maintenance, and operation of airplanes fitted with outward opening

cargo doors, and to make recommendations to prevent inadvertent cargo

door openings while the airplane is in flight. A design working group

was tasked with reviewing 14 CFR part 25.783 [and its accompanying

Advisory Circular (AC) 25.783-1, dated December 10, 1986] with the

intent of clarifying its contents and recommending revisions to enhance

future cargo door designs. This design group also was tasked with

providing specific recommendations regarding design criteria to be

applied to existing outward opening cargo doors to ensure that

inadvertent openings would not occur in the current transport category

fleet of airplanes.

The ATA task force made its recommendations in the ``ATA Cargo Door

Task Force Final Report,'' dated May 15, 1991 (hereinafter referred to

as ``the ATA Final Report''). On March 20, 1992, the FAA issued a

memorandum to the Director--Airworthiness and Technical Standards of

ATA (hereinafter referred to as ``the FAA Memorandum''), acknowledging

ATA's recommendations and providing additional guidance for purposes of

assessing the continuing airworthiness of existing designs of outward

opening doors. The FAA Memorandum was not intended to upgrade the

certification basis of the various airplanes, but rather to identify

criteria to evaluate potential unsafe conditions demonstrated on in-

service airplanes. Appendix 1 of this AD contains the specific

paragraphs from the FAA Memorandum that set forth the criteria to which

the outward opening doors should be shown to comply.

Applying the applicable requirements of CAR part 4b and design

criteria provided by the FAA Memorandum, the FAA has reviewed the

original type design of major transport airplanes, including Boeing 727

airplanes equipped with outward opening doors, for any design

deficiency or service difficulty. Based on that review, the FAA

identified unsafe conditions and issued, among others, the following

AD's:

[[Page 61549]]

For certain McDonnell Douglas Model DC-9 series airplanes:

AD 89-11-02, amendment 39-6216 (54 FR 21416, May 18, 1989);

For all Boeing Model 747 series airplanes: AD 90-09-06,

amendment 39-6581 (55 FR 15217, April 23, 1990);

For certain McDonnell Douglas Model DC-8 series airplanes:

AD 93-20-02, amendment 39-8709 (58 FR 471545, October 18, 1993);

For certain Boeing Model 747-100 and -200 series

airplanes: AD 96-01-51, amendment 39-9492 (61 FR 1703, January 23,

1996); and

For certain Boeing Model 727-100 and -200 series

airplanes: AD 96-16-08, amendment 39-9708 (61 FR 41733, August 12,

1996).

Using the criteria specified in the ATA Final Report and the FAA

Memorandum as evaluation guides, the FAA conducted an engineering

design review and inspection of an airplane modified in accordance with

STC's SA1797SO and SA1798SO (held by Aeronautical Engineers, Inc.). The

FAA identified a number of unsafe conditions with the main deck cargo

door systems of these STC's. The FAA design review team determined that

the design data of these STC's did not include a safety analysis of the

main deck cargo door systems.

For airplanes modified in accordance with STC SA1797SO, SA1798SO,

or SA1368SO, the FAA considers the following four specific design

deficiencies of the main deck cargo door systems to be unsafe:

1. Indication System

The main deck cargo door indication system for STC's SA1368SO and

SA1797SO uses warning lights at the door operator's control panel and a

light at the flight engineer's panel. These lights indicate the status

of the cargo door closed, latched and locked configurations. All three

conditions (i.e., door closed, latched, and locked) should be monitored

directly so that the door indication system cannot display either

``latched'' before the door is closed or ``locked'' before the door is

latched. The latch and lock sensors are wired in parallel and are tied

to a single indicator light. This design can illuminate the ``locked

light'' on the control panel of the main deck cargo door even if the

latches are latched but not locked. If a sequencing error causes the

door to latch and lock without being fully closed, the subject

indication system, as designed, may not alert the door operator or the

flight engineer of this condition. As a result, the airplane could be

dispatched with the main deck cargo door unsecured, which could lead to

the cargo door opening while the airplane is in flight and possible

loss of the airplane.

The light on the flight engineer's panel is labeled ``DOOR CARGO''

and is displayed in red since it indicates an event that requires

immediate pilot action. However, if the flight engineer is temporarily

away from his station, a door unsafe warning indication could be missed

by the pilots. In addition, the flight engineer could miss such an

indication by not scanning the panel. As a result, the pilots and

flight engineer could be unaware of, or misinterpret, an unsafe

condition and could fail to respond in the correct manner. Therefore,

an indicator light should be located in front of and in plain view of

both pilots since one of the pilot's stations is always occupied during

flight operations.

Based on the review of the electrical drawings of the door control

and door monitoring/annunication systems and observations from an

inspection of an airplane modified in accordance with the subject

STC's, the FAA concludes that latent failures (i.e., failures of system

components that are not monitored and would go undetected) in the

closed, latched, and locked functions may occur and lead to the main

deck cargo door opening during flight of the airplane.

The FAA has determined that the main deck cargo door indication

system of STC's SA1368SO, and SA1797SO also does not meet the

improbable level of reliability regarding false indication that is

considered adequate for safe operation. Many components are exposed to

the environment during cargo loading operations and may be contaminated

by precipitation, dirt, and grease, or damaged by foreign objects or

cargo loading equipment. As a result, wires, switches, and relays can

fail, jam, or short circuit and cause a loss of indication or a false

indication to the door operator and flight crew. The design logic of

the indication system (i.e., lights which extinguish when the door is

locked) could, in the event of latent failures that would extinguish

the light, result in an erroneous ``safe'' indication regardless of

actual door status.

STC's SA1368SO and SA1797SO lack a safety analysis of the main deck

cargo door systems. As a result, even though the light at the door

operator's control panel and the light at the flight engineer's panel

annunciate the status of closed, latched, and locked, a safety analysis

must be developed to show whether the design of the wiring of the main

deck cargo door monitoring system meets all FAA requirements.

2. Means to Visually Inspect the Locking Mechanism

The two view ports installed in accordance with STC's SA1797SO and

SA1368SO are located externally on the door for the purpose of viewing

locking pins at the No. 2 and No. 7 latch positions of the main deck

cargo door. These view ports are intended to allow the flight crew to

conduct a visual inspection of the cargo door locking mechanism to

determine whether the cargo door is closed, latched, and locked. The

view ports are used in conjunction with the door warning system and is

intended to provide a suitable back-up in the event that the main deck

cargo door warning system malfunctions.

However, because of the location of these view ports on the main

deck cargo door, a visual inspection may not result in the detection of

certain failures (e.g., bending or shearing of locking pins), and

consequently the airplane could be dispatched with the main deck cargo

door unsecured. Therefore, the FAA finds that these view ports are not

a suitable back-up when the cargo door warning system malfunctions.

As discussed in the ATA Final Report and the FAA Memorandum, there

must be a means of directly inspecting each lock or, at a minimum, the

locks at each end of the lock shaft of certain designs, such that a

failure condition in the lock shaft would be detectable.

3. Means to Prevent Pressurization to an Unsafe Level

Boeing 727-200 airplanes modified to install a cargo door in

accordance with STC SA1797SO are configured to utilize a mechanical

vent door for the purpose of preventing pressurization of the airplane

to an unsafe level in the event the main deck cargo door is not closed,

latched, and locked. However, Boeing 727-100 airplanes that have been

modified in accordance with STC SA1368SO do not have a vent door design

to prevent pressurization as part of the STC.

The results of an FAA inspection of the vent door linkage revealed

that the linkage design could exhibit single failures that could cause

the vent door to malfunction. A complete safety analysis of the vent

door mechanical design is necessary to identify and correct all such

malfunctions. No single failure of the mechanisms can defeat the

intended function of the vent door system.

4. Powered Lock Systems

The main deck cargo door control system for STC's SA1368SO and

[[Page 61550]]

SA1797SO that utilizes electrical interlock switches is designed to

remove door control power (electrical and hydraulic) prior to flight

and to prevent inadvertent door openings. Failure modes have been found

in the electrical portion of the door control panel, which, in turn,

activates the door control hydraulics. The potential for the occurrence

of these failure conditions is increased by the harsh operating

environment of freighter airplanes. Door system components are

routinely exposed to precipitation, dirt, grease, and foreign object

intrusion, all of which increase the likelihood of damage. As a result,

wires, switches, and relays have a greater potential to fail or short

circuit in such a way as to allow the cargo door to be powered open

without an operator's command and regardless of electrical interlock

positions.

A systems safety analysis would normally evaluate and resolve the

potential for these types of unsafe conditions. However, the FAA has

reviewed the design data for STC's SA1368SO and SA1797SO. The FAA finds

that the powered lock systems of the main deck cargo door do not comply

with criteria specified in Appendix 1 of this AD and considers the

design of these systems to be unsafe. The need for a system safety

analysis is identified in the ATA Final Report and the FAA Memorandum.

Since unsafe conditions have been identified that are likely to

exist or develop on other products of this same type design, this

proposed AD would require, within 60 days after the effective date,

revising the Limitations Section of the FAA-approved Airplane Flight

Manual (AFM) Supplement to provide the flight crew with procedures for

ensuring that the main deck cargo door is closed, latched, and locked

prior to dispatch of the airplane; and installing any associated

placards.

In addition, the proposed AD would require, within 36 months after

the effective date of the AD, incorporation of redesigned main deck

cargo door systems (e.g., warning/monitoring, power control, view

ports, and means to prevent pressurization to an unsafe level if the

main deck cargo door is not closed, latched, and locked), including any

associated procedures and placards that comply with the applicable

requirements of CAR part 4b and design criteria of the ATA Final Report

and the FAA Memorandum. Design data provided in support of the door

systems re-design should include a Systems Safety Analysis and

Instructions for Continued Airworthiness that are acceptable to the

FAA. Accomplishment of the incorporation of redesigned main deck cargo

door systems will prevent rapid decompression and/or structural damage

to the airplane as a result of loss or opening of the cargo door while

the airplane is in flight. The compliance time is based on the FAA's

assessment of the reasonable amount of time to incorporate redesigned

main deck cargo door systems. This time is in consideration of the 18-

month time period estimated by the Boeing 727 industry working group,

which includes operators, affected STC holders, and engineering

organizations, to develop FAA-approved redesigns.

These actions would be required to be accomplished in accordance

with a method approved by the FAA.

Cargo Barrier

In order to ensure the safety of occupants during emergency landing

conditions, the FAA first established in 1934, a set of inertia load

factors used to design the structure for restraining items of mass in

the fuselage. Because the airplane landing speeds have increased over

the years as the fleet has transitioned from propeller to jet design,

inertia load factors were changed as specified in CAR part 4b.260.

Experience has shown that an airplane designed to this regulation has a

reasonable probability of protecting its occupants from serious injury

in an emergency landing. The 727 passenger airplane was designed to

these criteria which specified an ultimate inertia load requirement of

9g in the forward direction. These criteria were applied to the seats

and structure restraining the occupants, including the flight crew, as

well as other items of mass in the fuselage.

When the 727 passenger airplane is converted to carry cargo on the

main deck, a cargo barrier is required, since most cargo containers and

the container-to-floor attaching devices are not designed to withstand

emergency landing loads. In fact, the FAA estimates that the container-

to-floor attaching devices will only support approximately 1.5g's to

3g's in the forward direction. Without a 9g cargo barrier, it is

probable that the loads associated with an emergency landing would

cause the cargo to be unrestrained and impact the occupants of the

airplane, which could result in serious injury or death.

The structural inadequacy of the cargo barrier was evident to the

FAA during its review in October 1997 of a Boeing 727 modified in

accordance with STC SA1798SO.

The observations revealed that the design of the cargo barrier

floor attachment and circumferential supporting structure does not

provide adequate strength to withstand the 9g forward inertia load

generated by the main deck cargo mass, nor does it provide a load path

to effectively transfer the loads from the cargo barrier to the

fuselage structure of the airplane. These observations are supported by

data contained in ``ER 2785, Structural Substantiation of the 50k 9g

Bulkhead Restraint System in Support of STC SA1543SO PN 53-1292-401 for

the 9g Bulkhead 53-1980-300 Assembly with Upper Attachment Structure,

Lower Attachment Structure, Floor Shear Web Structure, Seat Track

Splice Fittings, Seat Tracks, and Seat Track Splices,'' dated September

29, 1996, by M. F. Daniel. Although this report was specific to STC

SA1543SO, the FAA has determined that the data are applicable to

airplane modified in accordance with STC ST00015AT because the design

principles for attachment of the barriers in both STC's are the same.

The report reveals that structural deficiencies were found in the net

attach plates and floor attachment structure of the cargo barrier. The

data show large negative margins of safety, which indicate that the

inertia load capability of the cargo barrier is closer to 2g than the

required 9g in the forward direction. From these analyses, it is

evident that the cargo barrier would not be capable of preventing

serious injury to the occupants during an emergency landing event with

the full allowable cargo load.

Since unsafe conditions have been identified that are likely to

exist or develop on other products of this same type design, this

proposed AD would require installation of a main deck cargo barrier

that complies with the applicable requirements of CAR part 4b.

Accomplishment of the installation will prevent serious injury to

the occupants in the event of an emergency landing. The proposed

compliance time for the installation is within 36 months or 4,000

flight cycles after the effective date of the AD, whichever occurs

first. This compliance time is based on the FAA's assessment of the

reasonable amount of time to redesign, manufacture, and install the

cargo barrier. This time is consistent with estimates by affected STC

holders and operators that necessary redesigns can by developed and

approved by the FAA within 12 to 18 months from August 1998.

Regulatory Evaluation Summary

The regulations proposed herein would not have substantial direct

effects on the States, on the relationship between the national

government and the States, or on the distribution of

[[Page 61551]]

power and responsibilities among the various levels of government.

Therefore, in accordance with Executive Order 12612, it is determined

that this proposal would not have sufficient federalism implications to

warrant the preparation of a Federalism Assessment.

This analysis examines the cost of this proposed AD that would

require the installation of a fail-safe hinge, redesigned main deck

cargo door warning and power control systems, and a 9g cargo barrier on

Boeing Model 727 series airplanes that have been modified in accordance

with STC's held by Aeronautical Engineers, Inc. (AEI). As discussed

above, the FAA has determined that the main deck cargo door hinge is

not fail-safe, that certain main deck cargo door control systems do not

provide an adequate level of safety, and that the main deck cargo

barrier is not structurally adequate during a minor crash landing.

Approximately 72 U.S.-registered Boeing Model 727 series airplanes

would be affected by the proposed AD. The following discussion

addresses, in sequence, the actions in this proposed rulemaking and the

estimated cost associated with each of these actions. An analysis of

the cost is also available in Rules Docket No. 97-NM-233-AD.

1. Main Deck Cargo Door Hinge

Since unsafe conditions have been identified that are likely to

exist or develop on other modified Boeing Model 727 series airplanes,

paragraph (a) of the proposed AD would require, within 250 flight

cycles after the effective date of this AD, a one-time detailed visual

inspection to detect cracks of the external surface of the main deck

cargo door hinge. AEI estimates that this inspection would take 2 work

hours. At a mechanic's burdened labor rate of $60 per work hour, the

cost per airplane would be $120, or $8,640 for the 72 affected Boeing

Model 727 series airplanes.

Paragraph (b)(1) of the proposed AD would require, within 36 months

or 4,000 cycles after the effective date of this AD, a detailed visual

inspection of the mating surfaces of both the hinge and the door skin

and external fuselage doubler underlying the hinge. The FAA estimates

that compliance with this inspection would take 200 hours at an

estimated cost of $12,000 per airplane, or $224,400 for the entire

affected fleet of 72 airplanes.

Paragraph (b)(2) of the proposed AD would require installation of a

fail-safe door hinge. The compliance time for this installation also

would be 36 months, or 4,000 cycles after the effective date of this

AD. AEI estimates the cost to design and certificate such a hinge is

$25,000, that no parts for a fail-safe door hinge would be required,

and that the modification would take 50 hours. Total compliance costs

for this proposed provision for the affected fleet of 72 airplanes

would be $241,000.

Paragraph (c) of the proposed AD would require that, if any cracks

or discrepancies are detected during the inspections required by

paragraph (a) or (b)(1) of the proposed AD, repairs must be made prior

to further flight. The cost of these repairs is not attributable to

this proposed AD.

For purposes of this analysis, the FAA assumes an effective date of

July 1, 2000. The cost to comply with proposed paragraphs (a) through

(c) over the 36-month compliance period is $474,000 or $419,800

discounted to present value at 7 percent. The FAA assumes that the

installation of the main deck cargo door hinge [paragraph (b)(1)] would

be accomplished at the same time as the detailed visual inspection of

fastener holes [paragraph (b)(2)]. The FAA also assumes that the

affected carriers would perform these two activities uniformly

throughout the 36-month period. Finally, the certification cost for the

main deck cargo door hinge would be incurred within the first 6 months

after the effective date of the AD.

2. Main Deck Cargo Door Systems

Paragraph (d) of the proposed AD would require, within 60 days

after the effective date of this AD, a revision to the Limitations

Section of the FAA-approved AFM Supplement by inserting procedures to

ensure that the main deck cargo door is closed, latched, and locked

prior to dispatch of the airplane. In addition, paragraph (d) of the

proposed AD would require the installation of any associated placards.

The FAA assumes that Boeing Model 727 series airplanes converted

under a AEI STC will have an acceptable pressurization vent door

installed, which operators could use to visually determine whether the

vent is in the proper position prior to dispatch, indicating that the

door is closed, latched, and locked. The FAA estimates that this

activity would take no more than 30 minutes. Assuming each affected

airplane flies one flight per day, 260 days per year, the estimated

cost per inspection would be $30, or $7,800 per airplane per year until

the door system is changed, a total of $982,800 over 36 months.

Paragraph (e) of the proposed AD would require, within 36 months

after the effective date of this AD, incorporation of a redesigned main

deck cargo door system. The FAA estimates that the development and

certification of the system would cost $25,000. Modification parts

would cost $5,000 per airplane and labor costs would be $6,000 per

airplane for 100 hours. The FAA assumes that operators would

incorporate the redesigned main deck cargo door system during regularly

scheduled maintenance. The total costs of installing a redesigned main

deck cargo door system, including certification, parts, and labor would

be $817,000 over the 36-month period.

The total estimated cost to comply with proposed requirements for

the main deck cargo door system is $1.8 million, or $1.7 million,

discounted to present value.

3. Main Deck Cargo Barrier

Paragraph (f) of the proposed AD would require, within 36 months or

4,000 flight cycles after the effective date of this AD, installation

of a main deck cargo barrier that complies with the applicable

requirements of CAR part 4b. Ventura Aerospace holds an STC for an

approved 9g barrier, and the FAA estimates that operators whose

airplanes have been modified in accordance with AEI STC's would

purchase 9g barrier kits from Ventura Aerospace. The cost of a barrier

kit is $67,500. The FAA estimates that labor would cost $13,500 per

airplane and that an affected airplane would be out-of-service 3

additional days, at a cost of $15,000 per day, while this barrier is

installed.

The FAA assumes that operators would install 9g barriers uniformly

over the 36-month compliance period. The total non-discounted cost to

comply with paragraph (g) of the proposed AD would be $9.1 million, or

$7.8 million discounted to present value.

4. Alternative Methods of Compliance (AMOC) and Special Flight Permits

Paragraph (g) of the proposed AD would allow an AMOC or adjustment

of compliance time that provides an acceptable level of safety if

approved by the Manager of the Atlanta ACO. The FAA is unable to

determine the cost of an AMOC, but assumes it would be less than the

cost of complying with the proposed provisions in paragraphs (a)

through (f) of the proposed AD.

Paragraph (h) of the proposed AD would allow special flight permits

in accordance with the regulations to operate an affected airplane to a

location where the requirements of the proposed AD could be

accomplished.

5. Total Cost of the Proposed AD

The FAA estimates that the total compliance cost of the proposed AD

[[Page 61552]]

would be $11.3 million, or $10.0 million discounted to present value.

The Regulatory Flexibility Act (RFA) 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 RFA requires agencies to

solicit and consider flexible regulatory proposals and to explain the

rationale for their actions. The RFA 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 is that it will, the

Agency must prepare a regulatory flexibility analysis as described in

the RFA. 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 RFA 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.

The FAA estimates that 16 carriers operate airplanes that would be

affected by this proposed AD. Four of these operators are foreign

entities, 5 operators are large, and 7 operators are small, that is,

they employ fewer than 1,500 persons. The estimated total cost of the

proposed AD is $11.3 million, or approximately $157,600 for each of the

72 affected airplanes. Therefore, the FAA has determined that the

proposed rule would have a significant impact on a substantial number

of small entities and a regulatory flexibility analysis is required.

Under Section 63(b) of the RFA, the analysis must address:

1. Reasons why the agency is promulgating the rule;

2. The objectives and legal basis for the rule;

3. The kind and number of small entities to which the rule will

apply;

4. The projected reporting, recordkeeping, and other compliance

requirements of the rule; and

5. All federal rules that may duplicate, overlap, or conflict with

the rule.

These elements of the RFA are addressed below.

A. Reasons Why Agency Action Is Being Considered

The FAA has determined that the main deck cargo door hinge is not

fail-safe; that certain main deck cargo door control systems do not

provide an adequate level of safety; and the main deck cargo barrier is

not structurally adequate during a minor crash landing. The actions

specified in the proposed AD are intended to prevent structural failure

of the main deck cargo door hinge or failure of the cargo door system,

which could result in the loss or opening of the cargo door while the

airplane is in flight, and consequent rapid decompression and/or

structural damage to the airplane; and to prevent failure of the main

deck cargo barrier during an emergency landing, which could injure

occupants.

B. Statement of Objective and Legal Basis

Under the United States Code (U.S.C), the FAA Administrator is

required to consider the following matter, among others, as being in

the public interest: assigning, maintaining, and enhancing safety and

security as the highest priorities in air commerce. [See 49 U.S.C.

Sec. 44101(d).] 49 U.S.C. Sec. 44701(a) provides broad rulemaking

authority to ``promote safe flight of civil aircraft in air commerce.''

Accordingly, this proposed AD will amend Title 14 of the Code of

Federal Regulations to require operators of Boeing Model 727 series

airplanes that have been converted from a passenger- to a cargo-

carrying configuration to correct the identified unsafe condition.

C. Kind and Number of Small Entities

The RFA requires the FAA to determine whether or not a rule

significantly affects a substantial number of small entities. This

determination is typically based on small entity size and cost

thresholds that vary depending on the affected industry. The entities

affected by the rule are those operating U.S.-registered converted

Boeing Model 727 series airplanes. The FAA has determined that

approximately 7 of the 16 entities are small, i.e., employ fewer than

1,500 persons. These small entities operate between 1 and 9 affected

airplanes. Assuming the total costs of the proposed rule are divided

equally among the affected fleet of 62 airplanes, the costs per

airplane would be about $157,600. Therefore, the FAA has determined

that this proposed AD would significantly affect a substantial number

of small entities.

D. Projected Reporting, Recordkeeping, and Other Compliance

Requirements

With two minor exceptions, the rule will not mandate additional

reporting or recordkeeping. The proposed AD would require operators to

report results of the visual inspection of the main deck cargo door

hinge and the visual inspection of the fastener holes common to the

main deck cargo door hinge and underlying door and fuselage structure.

The cost of these reports is negligible.

E. Overlapping, Duplicative, or Conflicting Federal Rules

The rule will not overlap, duplicate, or conflict with existing

Federal rules.

F. Analysis of Alternatives

The FAA acknowledges that the rule will impose a financial

requirement on small entities. Therefore, the agency considered

alternatives to the proposed rule. These alternatives are:

Exclude small entities; and

Extend the compliance date for small entities.

The FAA has determined that the option to exclude small entities

from the requirements of the rule is not justified. The unsafe

condition that exists on an affected Boeing Model 727 series airplane

operated by a small entity is as potentially catastrophic as that on an

affected Model 727 series airplane operated by a large entity.

The FAA also considered options to extend the compliance period for

small operators. The Boeing 727 Freighter Industry Working Group, which

includes all affected U.S. operators (including small entities),

provided input on the incorporation of corrective actions for the door

hinge, door systems, and 9g barrier issues. The FAA initially proposed

a compliance time of 28 months, consistent with a related AD dealing

with the cargo floor structure on the same airplanes. The Industry

Working Group requested an extension to 36 months. Following review of

the Working Group's request, the FAA finds 36 months to be an

acceptable compliance time. Therefore, the FAA has, in fact, considered

and accepted this alternative and has accommodated small entity

concerns about compliance time.

Title II of the Unfunded Mandates Reform Act of 1995 (the Act),

enacted as Pub. L. 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

[[Page 61553]]

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 would 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.

This proposed AD does not contain any Federal intergovernmental or

private sector mandate. Therefore, the requirements of Title II of the

Unfunded Mandates Reform Act of 1995 do not apply.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration proposes to amend

part 39 of the Federal Aviation Regulations (14 CFR part 39) as

follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

Boeing: Docket 97-NM-233-AD.

Applicability: Model 727 series airplanes that have been

converted from a passenger to a cargo-carrying (``freighter'')

configuration in accordance with Supplemental Type Certificate (STC)

SA1368SO, SA1797SO, or SA1798SO; certificated in any category.

Note 1: This AD applies to each airplane identified in the

preceding applicability provision, regardless of whether it has been

otherwise modified, altered, or repaired in the area subject to the

requirements of this AD. For airplanes that have been modified,

altered, or repaired so that the performance of the requirements of

this AD is affected, the owner/operator must request approval for an

alternative method of compliance in accordance with paragraph (g) of

this AD. The request should include an assessment of the effect of

the modification, alteration, or repair on the unsafe condition

addressed by this AD; and, if the unsafe condition has not been

eliminated, the request should include specific proposed actions to

address it.

Compliance: Required as indicated, unless accomplished

previously.

To prevent structural failure of the main deck cargo door hinge

or failure of the cargo door system, which could result in the loss

or opening of the cargo door while the airplane is in flight, rapid

decompression, and structural damage to the airplane; and to prevent

failure of the main deck cargo barrier during an emergency landing,

which could injure occupants; accomplish the following:

Actions Addressing the Main Deck Cargo Door Hinge

(a) Within 250 flight cycles after the effective date of this

AD, perform a detailed visual inspection of the external surface of

the main deck cargo door hinge (both fuselage and door side hinge

elements) to detect cracks.

Note 2: For the purposes of this AD, a detailed visual

inspection is defined as: ``An intensive visual examination of a

specific structural area, system, installation, or assembly to

detect damage, failure, or irregularity. Available lighting is

normally supplemented with a direct source of good lighting at

intensity deemed appropriate by the inspector. Inspection aids such

as mirror, magnifying lenses, etc., may be used. Surface cleaning

and elaborate access procedures may be required.''

(b) Within 36 months or 4,000 flight cycles after the effective

date of this AD, whichever occurs first, accomplish paragraphs

(b)(1) and (b)(2) of this AD.

(1) Perform a detailed visual inspection of the mating surfaces

of both the hinge and the door skin and external fuselage doubler

underlying the hinge to detect cracks or other discrepancies (e.g.,

double or closely drilled holes, corrosion, chips, scratches, or

gouges). The detailed visual inspection shall be accomplished in

accordance with a method approved by the Manager, Atlanta Aircraft

Certification Office (ACO), FAA, Small Airplane Directorate. The

requirements of this paragraph may be accomplished prior to or

concurrently with the requirements of paragraph (b)(2) of this AD.

(2) Install a main deck cargo door hinge that complies with the

applicable requirements of Civil Air Regulations (CAR) part 4b,

including fail-safe requirements, in accordance with a method

approved by the Manager, Atlanta ACO.

(c) If any crack or discrepancy is detected during the detailed

visual inspection required by either paragraph (a) or (b)(1) of this

AD, prior to further flight, repair in accordance with a method

approved by the Manager, Atlanta ACO.

Actions Addressing the Main Deck Cargo Door Systems

(d) Within 60 days after the effective date of this AD, revise

the Limitations Section of the FAA-approved Airplane Flight Manual

(AFM) Supplement by inserting therein procedures to ensure that the

main deck cargo door is closed, latched, and locked prior to

dispatch of the airplane, and install any associated placards. The

AFM revision procedures and installation of any associated placards

shall be accomplished in accordance with a method approved by the

Manager, Atlanta ACO.

(e) Within 36 months after the effective date of this AD,

incorporate redesigned main deck cargo door systems (e.g., warning/

monitoring, power control, view ports, and means to prevent

pressurization to an unsafe level if the main deck cargo door is not

closed, latched, and locked), including any associated procedures

and placards, that comply with the applicable requirements of CAR

part 4b and criteria specified in Appendix 1 of this AD; in

accordance with a method approved by the Manager, Atlanta ACO.

Note 3: The design data submitted for approval should include a

Systems Safety Analysis and Instructions for Continued Airworthiness

that are acceptable to the Manager, Atlanta ACO.

Actions Addressing the Main Deck Cargo Barrier

(f) Within 36 months or 4,000 flight cycles after the effective

date of this AD, whichever occurs first, install a main deck cargo

barrier that complies with the applicable requirements of CAR part

4.b, in accordance with a method approved by the Manager, Atlanta

ACO.

Note 4: The maximum main deck total payload that can be carried

is limited to the lesser of the approved cargo barrier weight limit,

weight permitted by the approved maximum zero fuel weight, weight

permitted by the approved main deck position weights, weight

permitted by the approved main deck running load or distributed load

limitations, or approved cumulative zone or fuselage monocoque

structural loading limitations (including lower hold cargo).

Note 5: Installation of a Ventura Aerospace Inc. cargo barrier

STC ST00848LA is an approved means of compliance with the

requirements of paragraph (f) of this AD.

(g) An alternative method of compliance or adjustment of the

compliance time contained in this proposal that provides an

acceptable level of safety may be used if approved by the Manager,

Atlanta ACO. Operators shall submit their requests through an

appropriate FAA Principal Maintenance Inspector, who may add

comments and then send it to the Manager, Atlanta ACO.

Note 6: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Atlanta ACO.

(h) Special flight permits may be issued in accordance with

sections 21.197 and 21.199 of the Federal Aviation Regulations (14

CFR 21.197 and 21.199) to operate the airplane to

[[Page 61554]]

a location where the requirements of this AD can be accomplished.

Appendix 1

Excerpt from an FAA Memorandum to the Director--Airworthiness

and Technical Standards of ATA, dated March 20, 1992.

``(1) Indication System:

(a) The indication system must monitor the closed, latched, and

locked positions, directly.

(b) The indicator should be amber unless it concerns an outward

opening door whose opening during takeoff could present an immediate

hazard to the airplane. In that case the indicator must be red and

located in plain view in front of the pilots. An aural warning is

also advisable. A display on the master caution/warning system is

also acceptable as an indicator. For the purpose of complying with

this paragraph, an immediate hazard is defined as significant

reduction in controllability, structural damage, or impact with

other structures, engines, or controls.

(c) Loss of indication or a false indication of a closed,

latched, and locked condition must be improbable.

(d) A warning indication must be provided at the door operators

station that monitors the door latched and locked conditions

directly, unless the operator has a visual indication that the door

is fully closed and locked. For example, a vent door that monitors

the door locks and can be seen from the operators station would meet

this requirement.

(2) Means to Visually Inspect the Locking Mechanism:

There must be a visual means of directly inspecting the locks.

Where all locks are tied to a common lock shaft, a means of

inspecting the locks at each end may be sufficient to meet this

requirement provided no failure condition in the lock shaft would go

undetected when viewing the end locks. Viewing latches may be used

as an alternate to viewing locks on some installations where there

are other compensating features.

(3) Means to Prevent Pressurization:

All doors must have provisions to prevent initiation of

pressurization of the airplane to an unsafe level, if the door is

not fully closed, latched and locked.

(4) Lock Strength:

Locks must be designed to withstand the maximum output power of

the actuators and maximum expected manual operating forces treated

as a limit load. Under these conditions, the door must remain

closed, latched and locked.

(5) Power Availability:

All power to the door must be removed in flight and it must not

be possible for the flight crew to restore power to the door while

in flight.

(6) Powered Lock Systems:

For doors that have powered lock systems, it must be shown by

safety analysis that inadvertent opening of the door after it is

fully closed, latched and locked, is extremely improbable.''

Issued in Renton, Washington, on November 4, 1999.

D. L. Riggin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 99-29474 Filed 11-10-99; 8:45 am]

BILLING CODE 4910-13-U