Airworthiness Standards; Crash Resistant Fuel Systems in Normal and Transport Category Rotorcraft; Final Rule DEPARTMENT OF TRANSPORTATION

Federal RegisterOct 3, 1994

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SUMMARY: These amendments add comprehensive crash resistant fuel system

design and test criteria to the airworthiness standards for normal and

transport category rotorcraft. Application of these standards will

minimize fuel spillage near ignition sources and potential ignition

sources and, therefore, will improve the evacuation time needed for

crew and passengers to escape a post-crash fire (PCF). Implementation

of these amendments will minimize the PCF hazard saving lives and

substantially reducing the severity of physiological injuries sustained

from PCF's in otherwise survivable accidents.

EFFECTIVE DATE: November 2, 1994.

FOR FURTHER INFORMATION CONTACT: Mr. Mike Mathias, Regulations Group,

ASW-111, Rotorcraft Directorate, Aircraft Certification Office, FAA,

Fort Worth, Texas 76193-0111, telephone number (817) 624-5123.

SUPPLEMENTARY INFORMATION:

Background

These amendments are based on a Notice of Proposed Rulemaking

(NPRM) No. 90-24, issued September 27, 1990 (55 FR 41000, October 5,

1990). A correction to the NPRM was published on December 11, 1990 (55

FR 50931).

Post-crash fires (PCF's) are the primary cause of fatalities and

injuries in otherwise survivable impacts resulting from rotorcraft

accidents. It is estimated that 5 percent of the occupants in

survivable rotorcraft accidents are killed or injured by PCF's

annually. These types of fatalities and traumatic injuries will be

substantially reduced by the implementation of the design and test

criteria of this amendment. Nearly all PCF's are caused by crash-

induced fuel leaks that quickly come in contact with ignition sources

during or after impact. The fuel containment and hazard elimination

provisions contained in this amendment will, in the majority of cases,

give occupants the time necessary to escape a survivable crash before a

post-crash fire (PCF) could become life threatening. A crash resistant

fuel system (CRFS) would not be expected to prevent all fires; however,

a CRFS would, in the majority of survivable accidents, either prevent a

PCF or delay the massive fire, or fireball, long enough to allow the

occupants to escape. These standards have been validated by military

safety statistics as significantly minimizing the PCF hazard and its

associated fatalities and injuries.

Discussion of Comments

General

Thirteen commenters, including representatives from small and large

U.S. helicopter manufacturers, foreign airworthiness authorities, and

foreign helicopter manufacturers, commented on the NPRM. All commenters

agree with the FAA that CFRS installations will improve occupant

survivability in parts 27 and 29 rotorcraft.

The majority of commenters fully support all of the proposals. No

commenter opposes adoption of the proposed amendments. One commenter

proposes adoption of more stringent standards, and several commenters

offer other counterproposals and recommendations for specific

proposals.

General Comments on the Proposals

Unless specifically noted otherwise, the comments and responses

apply to both proposed Secs. 27.952 and 29.952, since the requirements

in both are identical.

The Use of the Term ``Flammable Fluid''

Flammable fluids other than fuel should not be included in the

amendments, since all on-board light and heavy oil systems are

affected. Accordingly, the commenter proposes that ``flammable fluid''

be changed to ``fuel.'' The FAA agrees with this comment, and

appropriate changes have been made.

Accuracy of the Economic Analysis

One commenter questions the accuracy of the economic analysis but

offers no specific recommendations or corrections. The FAA has

reevaluated the analysis and found no changes were necessary based on

this comment.

Rigidity of the Proposals

A commenter states that the proposed amendments are ``too rigid''

in their approach and limit the designers' choices. The FAA disagrees.

Although the 50-foot drop height and certain strength requirements are

specific, these and most of the other requirements do not mandate

specific designs. Objective rules allow flexibility in showing

compliance. An example of this flexibility is that bladders are not

mandated; the rule specifies only freedom from leakage after impact.

The amendments are intended to be as flexible as possible to allow

design innovation while at the same time requiring a specific safety

standard for a CRFS.

Level of Detail in the Proposals

A commenter states that the amendments include some very detailed

requirements that are more appropriate for a Technical Standard Order

(TSO). The FAA agrees that some of the details proposed for paragraphs

27.952 (e) and (f) and 29.952 (e) and (f) should not be regulatory

requirements, are more appropriate for an advisory circular, and should

not be part of the proposed standard. Therefore, those details have

been removed and placed in the draft advisory material. However, the

FAA disagrees with the commenter that the level of detail either in the

proposals or in the advisory material would necessitate a CRFS TSO.

The Standardized Approach of the Proposals

A commenter believes that the standardized design and test approach

of these amendments to CRFS certification, while acceptable, is not as

valid as the establishment of individual design criteria on a case-by-

case basis followed by a design review and a test program. However, the

commenter offered no specific data or case histories to substantiate

this position. Since all past successful civil and military experience

has been with a standardized design and test approach, the FAA finds no

historical or technical basis to support the commenter. Moreover, the

FAA has determined that a standardized design and test approach, when

properly applied, still allows for adequate use of individual design

features that meet the specific safety standards.

Military Standards

A commenter expresses concern that the proposals are less stringent

than the corresponding military standard because of perceived

differences in the military and civil environments. The commenter is

especially concerned that fuel tank bladders are not mandated. The

commenter proposes verbatim adoption of the military standards. The FAA

disagrees. Based on independent studies, the General Aviation Safety

Panel (GASP) committee recommendations, and past civil CRFS service

experience, the FAA has determined that the proposals, while less

stringent than the military standard, provide an equivalent level of

safety considering the differences (such as violent atypical flight

maneuvers, landing maneuvers, and gunfire hazards) in the civil and

military environments. While it is anticipated that most successful

fuel cell designs will involve the use of bladders, bladderless rigid

designs (that provide the same level of safety as designs with

bladders) may be approved under the new standard.

Comment Concerning Performance Criteria Specification

One commenter applauds the fact that the proposal specified

performance standards (i.e., a minimum level of safety) in lieu of

unnecessarily mandating certain specific design features such as

flexible liners.

Comments on Specific Proposals

Comments on Section 27.561(d)

A commenter questions the need for the specification of load

factors in proposed Sec. 27.516(d), since similar load factors are

specified in proposed Sec. 27.952(b)(3). The FAA has determined that

load factors are needed in both Secs. 27.561(d) and 27.952(b)(3).

Section 27.561(d) applies to fuselage structure, and Sec. 27.952(b)(3)

applies to fuel tanks. Although the load factors are identical, they

are specified for different parts of the rotorcraft.

Another commenter correctly states that the load factors are

clearly specified for fuel cells by their location on the rotorcraft

but asks which load factors are to be used for other major fuel system

components. The load factors used for each fuel cell location should be

used for fuel cell components of significant mass in the same

locations. Therefore, this amendment is adopted as proposed.

Comments on Sections 27.952(a) and 29.952(a)

A commenter states that identification of a critical fuel tank (if

such exists) should not be allowed in certification. The FAA does not

agree. The use of critical conditions, systems, etc., is a well-

established technique for substantiating similar design features.

Therefore, these amendments are adopted as proposed.

Comments on Sections 27.952(a)(1) and 29.952(a)(1)

All commenters support the proposed drop test, and most commenters

favor the 50-foot drop height. However, two commenters propose a

reduction in the drop height for a bare fuel cell from 50 to 25 feet.

Another commenter proposed a reduction in drop height of a fuel cell

test article configuration (i.e., a fuel cell installed in its

representative airframe structure) from 50 to 15 feet. Another

commenter contends that since the military fuel cell drop test (and

nearly 20 years of associated, successful safety experience) is at a

65-foot drop height, the proposed drop height should be 65 feet, not 50

feet. The proposed 50-foot drop height is based, in part, on an

analysis of nearly 20 years of combined military and civilian design

and operational data. (The 15-foot reduction in drop height from the

military standard to the proposed civil standard equates their level of

safety because of the elimination of the additional risks associated

with the military environment.) A significant part of this 20 years of

data is based on approximately 1,500 civil rotorcraft that have been

certificated (on a voluntary, nonhazard basis) to design standards

(including a 50-foot drop test) analogous to these proposals. This 20

years of data and experience (from both the military and voluntary

civil unit installations) have resulted in a good operational safety

record. This good safety record indicates that fuel tank installations

designed to these proposals (including the practical standard of a 50-

foot drop height) successfully minimize the post-crash fire hazard.

Therefore, no change to the 50-foot drop height is warranted.

Another commenter proposes deletion of the requirement to drop the

fuel cell in its surrounding structure. The same commenter asks if the

bare tank drop test will follow the procedure of MIL-T-27422B when the

surrounding structure is free of projections or design features likely

to contribute to tank ruptures. Another commenter states that the

requirement to drop a representative structure should be fully defined.

The same commenter states that no mention is made of production drop

test requirements that would be made necessary by postproduction design

changes to either the fuel system or its surrounding structure. The FAA

considers these suggested changes unnecessary because (under Part 21) a

design review (precipitated by a proposed design modification that

affects the fuel cell-airframe interface) would automatically require a

review of the interface with regard to these proposed standards. If

that design review shows the surrounding structure is free of

projections and hazards, the fuel cell may be dropped alone.

Additionally, MIL-T-27422B procedures may be used, except that the drop

height is reduced to 50 feet. Further, major post certification design

changes, such as major changes to the fuel system cells or their

locations, automatically require recertification in accordance with FAR

21.93(a). Therefore, the amendments are adopted as proposed.

Comments on Sections 27.952(a)(3) and 29.952(a)(3)

A commenter notes that the proposed drop test criteria require that

the fuel cell test article be filled 80 percent with water with no

mention of the contents of the other 20 percent. The commenter states

that this is different from part 23 Notice No. 85-7A (55 FR 7280,

February 28, 1990) in that the proposed rotorcraft amendments do not

require the air to be removed from the fuel cell prior to the drop

test. The commenter suggests that the best method of compensating for

the difference between the density of fuel and water is to leave the

tank 100 percent full of fuel and adjust the drop height to a lower

value.

The FAA notes that the drop test criteria proposed in Notice 90-24

are the same as those proposed in part 23 Notice 85-7A and the same as

those used to comply with MIL-T-27422B. There are standard, acceptable

methods of configuring (i.e., properly removing the air from) a soft

flexible fuel cell, and there are standard, acceptable methods of

configuring (i.e., properly removing the air from) the vents on a rigid

fuel cell. The air removal methods intended by these proposals are the

same as those used to comply with MIL-T-27422B and are accepted,

industry practice. It is impracticable to remove a significant amount

of air from many rigid fuel cell designs by pulling a vacuum without

either inducing unacceptable stresses or causing structural failure.

Extreme vacuum conditions inside fuel tanks do not exist in practice.

However, natural venting (involving partial vacuums) exists for rigid

tanks in a pre-crash, falling condition. A natural partial vacuum

condition is intended to be duplicated for rigid tanks by allowing

normal vent function during the drop test. Flexible fuel cells will

have the air removed by hand (i.e., by pushing out the air and

resealing the bag) prior to the drop as is currently practiced by the

industry.

The method chosen to compensate for the density of water versus

that of fuel (i.e., 80 percent full of water) is a standard method. It

is used successfully by the civil rotorcraft industry. The commenter's

alternate method of reducing the drop height has some merit but is not

supported by current, known data.

Therefore, these amendments are adopted as proposed.

Comments on Sections 27.952(a)(4) and 29.952(a)(4)

A commenter notes that the amendments differ from MIL-T-27422B, in

that the amendments require that the tank be dropped in its surrounding

structure, unless it is clearly shown that the structure is free from

projections and other such hazards. The commenter suggests that the FAA

not adopt the requirement to drop the tank in the surrounding

structure. The FAA disagrees. The FAA concluded that in the interests

of safety the tank should be dropped in its surrounding structure. Only

when all projections and other puncture hazards have been minimized by

design will dropping a bare fuel cell suffice to show compliance. The

FAA's approach improves on the MIL-T-27422B criteria in that an FAA-

approved, documented certification design review will be required to

minimize the surrounding airframe projections and other puncture

hazards prior to a bare tank drop test. Therefore, the amendments are

adopted as proposed.

Comments on Sections 27.952(b) and 29.952(b)

A commenter states that the load factors proposed in these sections

are redundant to those contained in structural Secs. 27.561 and

29.561(d), that no procedures to conduct these tests have been defined,

and that the cost of this type of testing is not addressed. Two other

commenters question the need for specification of separate load factors

by rotorcraft zone (i.e., location) for fuel cells that exceed the

standard airframe load factors. The FAA disagrees that the proposed

load factors are redundant. They are for fuel cells and major mass

items in the fuel system only. The load factors are to be used in

standard structural analysis to structurally design the fuel cells,

other major fuel system mass items, and their attachments. No special

tests, other than the required structural substantiation tests are

intended. No costs have been added since the required structural

analysis and test programs are already conducted during certification

for these components to the current load factors. The separate load

factor specification by zone is necessary to provide proper crash

resistance for occupant safety and PCF prevention for fuel system

components located in three selected zones of the rotorcraft. They also

provide the designer with specific criteria (i.e., load factors) for

proper static analysis of fuel system components in these specific

zones. The load factors proposed by Secs. 27.952(b) and 29.952(b) are

for fuel system components only; whereas, the load factors of current

Sec. 29.561(d) are for the airframe only. However, load factors for

fuel system components and airframe components are compatible.

Therefore, the amendments are adopted as proposed.

Comments on Sections 27.952(b)(2) and 29.952(b)(2)

A commenter suggests that the words ``* * * that if loosened could

injure an occupant in an emergency landing * * *.'' be removed from

Secs. 27.952(b)(2) and 29.952(b)(2). The commenter believes removal to

be necessary because this phrase is intended to minimize a

``mechanical'' ballistic hazard from fuel system components and not a

PCF hazard. The amendments, in the commenter's view, are only intended

to minimize a PCF. The commenter's presumption is incorrect. The

amendments are intended to provide a CRFS. This includes preventing

impact-induced, ballistic hazards to fuel system components as well as

PCF hazards. Therefore, the amendments are adopted as proposed.

Comments on Sections 27.952(c) and 29.952(c)

A commenter believes that the proposed amendments mandate self-

sealing breakaway couplings and suggests that the amendments be revised

to include the words ``Where hazardous relative motion of fuel system

components is likely to exist during a crash, breakaway self-sealing

couplings shall be required.'' Another commenter suggests that no

alternate, equivalent designs to breakaway fuel fittings be allowed by

the amendments. A third commenter points out that there is no mention

of any pull-out strength requirements for fuel tank fittings as stated

in MIL-T-27422B. The amendments already express the intent of the

wording suggested by the first commenter concerning hazardous relative

motion. Further, the FAA does not agree with the second comment that

alternate, equivalent designs to breakaway fuel fittings should not be

allowed, since several proven, alternate, equivalent designs have

already been approved. Thus, alternate, equivalent designs for

breakaway fuel fittings are acceptable. In response to the third

commenter, fitting strength and hose pull-out strength requirements of

MIL-T-27422B are industry practice and are acceptable as one means of

compliance. Therefore, the amendments are adopted as proposed.

Comments on Sections 27.952(c)(1)(iii) and 29.952(c)(1)(iii)

A commenter suggests that Secs. 27.952(c)(2)(iii) and

29.952(c)(1)(iii) be changed to specify leakage as one method of

detecting an unlocked or otherwise faulty breakaway coupling. The FAA

agrees that leakage is one method of detecting an unlocked coupling but

finds that the proposed wording of ``design provisions to visually

ascertain'' adequately covers consideration of leakage as a means to

verify locking of the couplings. Therefore, the amendments are adopted

as proposed.

Comments on Sections 27.952(c)(1)(v) and 29.952(c)(1)(v)

A commenter suggests that Secs. 27.952(c)(1)(v) and 29.952(c)(1)(v)

be changed to allow ``fuel seepage'' after a breakaway coupling has

performed its intended function. The FAA agrees with the intent of the

comment but has determined that this kind of detail is more appropriate

in advisory guidance material. It is intended that industry practice,

which allows loss of entrapped fuel (up to 8 ounces) and fuel seepage

(up to 5 drops per minute), be acceptable after the valve has

functioned. Therefore, the amendments are adopted as proposed.

Comments on Sections 27.952(d) and 29.952(d)

A commenter suggests adding a sentence between the second and third

sentences of Secs. 27.952(d) and 29.952(d) as follows: ``For tanks

using a flexible tank or flexible liner, all filler caps and tank

fittings attached to structure in locations of anticipated structural

deformation must be frangibly attached such that the tank fittings and

filler caps stay with the fuel tank to preclude tank ruptures after the

frangible separation.'' The FAA agrees with the intent of this comment

but finds that no change is necessary in the final rule. The FAA

understands the commenter is suggesting that compliance methodology

rather than objective substance be included in the rule. Therefore, the

amendments are adopted as proposed.

Comments on Sections 27.952(d)(1) and 29.952(d)(1)

A commenter suggests that the FAA remove the second sentence from

Secs. 27.952(d)(1) and 29.952(d)(1), which reads as follows: ``To

prevent inadvertent separation or deformation, the load must be 10

times the normal service loads at the frangible or deformable

attachment location.'' The FAA recognizes the large variance in

industry design practice in calculating this particular ratio and in

setting its specific value. Accordingly, the FAA agrees with the

commenter, and the sentence is removed from the final rule. Therefore,

these amendments are adopted as revised.

Comments on Sections 27.952(e)(1) and 29.952(e)(1)

A commenter states that the proposed Secs. 27.952(e)(1) and

29.952(e)(1) criteria largely repeat existing criteria. The commenter

provides several specific examples of the perceived repetition. Another

commenter asks why airframe mounted fuel filters are not acceptable in

the engine compartment (i.e., fire zone) if engine mounted filters are

acceptable. The FAA maintains that the proposed sections relate to a

post-crash configured rotorcraft, that is radically different in terms

of ignition sources, fuel leaks, and geometry than a pre-crash

configured rotorcraft even though similarities may exist. Prior to

these proposed amendments, parts 27 and 29 applied only to pre-crash

(or flight) configured rotorcraft. Also, the proposed sections refer to

the entire rotorcraft, not just specific zones, such as the pre-crash

configured exhaust system regulations that were cited by the commenter

in a particular example. However, because of this and other related

comments, the FAA has decided to simplify the final rule by deleting

the proposed subsections relating to compliance methodology and moving

the term ``occupiable areas'' from proposed paragraphs e(4) to revised

paragraphs (e).

With respect to the comment concerning the use of airframe mounted

fuel filters, the FAA agree that airframe mounted fuel filters, as well

as engine mounted fuel filters inside the engine fire zone, are

acceptable. Therefore, Secs. 27.952(e) and 29.952(e) are adopted as

revised; and Secs. 27.952(e)(1), (e)(2), (e)(3), (e)(4); 29.952(e)(1),

(e)(2), (e)(3) and (e)(4) are deleted.

Comments on Sections 27.952(e)(4) and 29.952(e)(4)

A commenter states that the existing rules are adequate to ensure

sufficient PCF protection for fuel tanks located near occupiable areas.

Therefore, from a practical view, sufficient separation cannot be

economically achieved to the extent that it would have a significant

impact on preventing a PCF. Thus, the commenter suggests that

Secs. 27.952(e)(4) and 29.952(e)(4) be removed. In contrast, the FAA

believes that it is practical to enhance PCF safety through design

changes under proposed Secs. 27.952(e)(4) and 29.952(e)(4). For

example, moving a fuel cell an additional \1/4\ or more inches aft of

an occupied volume (within the maximum practicable extent of a given

design envelope) could avoid a major, occupant-drenching, post-crash

fuel spill (and potential PCF). This could be accomplished by simply

adding \1/4\ or more inches of crushable, energy absorbing airframe

distance between the occupied volume and the fuel cell. Such a design

decision would not need to be considered under the current standards.

Under these proposals it would have to be considered. As stated

previously, Secs. 27.952(e)(4) and 29.952(e)(4) have been removed in

order to simplify the final rule by deleting the compliance

methodology. However, the requirement for separation of fuel tanks from

occupiable areas is adopted in Secs. 27.952(e) and 29.952(e).

Comments on Sections 27.952(e) and 29.952(e)(5)

Three commenters correctly observe that Secs. 27.952(e)(5) and

29.952(e)(5) contained the incorrect reference, ``* * * (as defined by

paragraph (b) of this section) * * *.'' The FAA agrees. As stated

previously, Secs. 27.952(e)(5) and 29.952(e)(5) have been removed in

order to simplify the final rule by deleting the compliance

methodology.

Comments on Sections 27.952(e)(6) and 29.952(e)(6)

A commenter states that, under his interpretation, proposed

Secs. 27.952(e)(6) and 29.952(e)(6) would require firewalls to retain

their sealing ability under the load factors of Secs. 27.952(b)(1) and

29.952(b)(1)). The commenter believes that all large mass items, such

as engines and cowlings, in the vicinity of the firewall would have to

be restrained to prevent impact-induced firewall ruptures (i.e.,

preserve postimpact sealing ability). The commenter further believes

that, based on other common design requirements such as fuel line

penetrations of firewalls, the proposed amendment is impractical.

Another commenter concurs with the proposed firewall survivable impact

sealing retention requirement, but is concerned that a direct

application of the proposed Secs. 27.952(b)(1) and 29.952(b)(1) load

factors would produce a stiff, heavy firewall that, while able to

retain sealing capability, would be heavy, uneconomical, and not have

the intended crash-resistant design features.

The commenters misinterpreted the intent of proposed

Secs. 27.952(e)(6) and 29.952(e)(6). These proposals are based on

similar MIL-STD-1290 requirements that have been used in design for

many years. The FAA does not intend that a firewall designed to the

load factors of Secs. 27.952(b)(1) and 29.952(b)(1) would retain its

complete sealing ability under all post-crash threats. Thus, some

leakage around typical vent and line penetrations and other small post-

crash penetrations of the firewall in a survivable impact are

acceptable. Unless an obvious, catastrophic hazard would be created in

a survivable impact by atypical design features, restraint of the

engines and cowling to prevent impact-induced firewall rupture was not

intended. The FAA intends that the firewall retain its sealing ability

in a survivable impact. The most significant problem addressed during

the firewall design is deformation of the firewall induced by fuselage

deformations under crash conditions.

Concerning the second comment, the FAA does not agree that the

proposed requirement will result in stiff, heavy firewalls. The

requirement can be met by a firewall of a low stiffness, ductile design

that can withstand the maximum vertical, lateral, and horizontal

crushing displacements that are estimated to occur in a survivable

impact. A low stiffness, ductile design can efficiently accommodate

crash-induced deformations without shearing fuel or electrical lines

and without rupturing or otherwise losing its gross sealing ability

(i.e., creating a major ignition source or fire path). A displacement

based firewall certification test should be conducted that shows that

it is capable of performing its intended gross sealing function in a

survivable impact. As stated previously, in order to simplify the final

rule by deleting the compliance methodology, new Secs. 27.952(e) and

29.952(e) are adopted as revised, and proposed Secs. 27.952(e)(6) and

29.952(e)(6) are removed.

Comments on Sections 27.952(e)(1)(iv) and 29.952(e)(1)(iv)

A commenter suggests that Secs. 27.952(e)(1)(iv) and

29.952(e)(1)(iv) be modified to add the phrase ``* * * if it can be

considered an ignition source,'' to the end of the last sentence. The

commenter correctly states that not all hot surfaces should be

considered as ignition sources. The FAA agrees. As stated previously,

Secs. 27.952(e)(1)(iv) and 29.952(e)(1)(iv) have been removed; new

Secs. 27.952(e) and 29.952(e) adequately incorporate the substance of

this comment.

Comments on Sections 27.952(e)(1)(v)

A commenter notes that the word ``not'' was omitted between

``must'' and ``be'' in the second sentence of Secs. 27.952(e)(1)(v).

The FAA agrees. The error was discovered after publication of the

proposed rule, and a correction was published in the Federal Register

on December 11, 1990 (55 FR 50931).

Comments on Sections 27.952(f) and 29.952(f)

A commenter recommends placing the detailed design criteria

proposed by Secs. 27.952(f) and 29.952(f) in an advisory circular

retaining only a shortened lead-in version of Secs. 27.952(f) and

29.952(f). Another commenter believes that Secs. 27.952(f) and

29.952(f), while acceptable in principle, duplicate many current FAR

requirements and several other sections of 27.952 and 29.952. The

commenter cited several examples of perceived duplication. The FAA

agrees with the first commenter's proposal to place detailed design

criteria in the advisory circular material. Therefore, proposed

Secs. 27.952(f)(1) through 27.952(f)(9) and 29.952(f)(1) through

29.952(f)(9) are removed. Sections 27.952(f) and 29.952(f) are revised

to replace the proposed, detailed design criteria specified after the

phrase ``as follows:'' with a less detailed design criteria indicated

by the phrase,'' * * * to be crash resistant * * *.'' Therefore, these

amendments are adopted as revised. Additionally, this revision answers

the second commenter's perceived duplicity concerns.

Another commenter notes that the word `long' used in line 4 of

Sec. 29.952(f)(5) should be `along'. The FAA agrees but no correction

is necessary since this proposed paragraph was removed.

Comments on Sections 27.952(g) and 29.952(g)

A commenter suggests that requirements for impact and tear

resistance be included in the amendments. The commenter correctly notes

that the GASP report recommends specific impact and tear resistance

values for civil rotorcraft based on MIL-T-27422B requirements. The FAA

agrees with the comment in general but notes that proposed

Secs. 27.952(g) and 29.952(g) objectively requires that crash-resistant

fuel cells be tear and impact resistant. Further, it is intended that

paragraphs 4.6.5.1 through 4.6.5.5 of MIL-T-27422B (modified for the

civil environment) may be used to provide one acceptable method of

properly assessing impact and tear resistance. Therefore, the

amendments are adopted as proposed.

Comments on Sections 27.952(h) and 29.952(h)

Two commenters state that Secs. 27.952(h) and 29.952 (h) and (b)

are redundant. The FAA agrees. Therefore, proposed Secs. 27.952(h) and

29.952(h) are deleted.

Comments on Sections 27.975(b) and 29.975(a)(7)

A commenter states full support for Secs. 27.975(b) and

29.975(a)(7), which propose that the venting system be designed to

minimize spillage of fuel through the vents to an ignition source in

the event of a rollover. However, the comment suggests deletion of the

phrase ``* * * is shown to be extremely improbable * * *'' because, in

his view, in practical terms, it would be impossible for an applicant

to demonstrate such a low probability. The FAA agrees. The current term

``extremely remote'' rather than ``extremely improbable'' was intended.

The FAA has determined that ``extremely remote'' is the correct term.

The amendments are adopted as proposed except for replacing the word

``improbable'' with the word ``remote.''

Regulatory Evaluation Summary

Executive Order 12866 dated September 30, 1993, directs Federal

agencies to promulgate new regulations and maintain current regulations

only if they are required by law, are necessary to interpret the law,

or are made necessary by a ``compelling public need.'' The order also

requires that agencies assess all costs and benefits of available

regulatory alternatives and select the alternative that maximizes the

net benefits and imposes the least burden on society.

Additionally, the order requires agencies to submit a list of all

rules, except those specifically exempted by the Office of Information

and Regulatory Affairs (OIRA) because they respond to emergency

situations or other narrowly defined exigencies, to determine if the

rules constitute ``significant regulatory action.'' ``Significant

regulatory action'' means an action that is likely to result in a rule

that may (1) have an annual effect on the economy of $100 million or

more or adversely affect in a material way the economy, a sector of the

economy, productivity, competition, jobs, the environment, public

health or safety, or state, local, or tribal governments or

communities; (2) create a serious inconsistency or otherwise interfere

with an action taken or planned by another agency; (3) materially alter

the budgetary impact on entitlements, grants, user fees, or loan

programs or the rights and obligations of recipients thereof; or (4)

raise novel legal or policy issues arising out of legal mandates, the

President's priorities, or the principles set forth in the Executive

Order. ``Significant regulatory action'' is submitted to centralized

regulatory review by OIRA.

OIRA and the FAA have determined that this rule is not ``a

significant regulatory action.'' However, a cost-benefit analysis,

including evaluation of cost-reducing alternatives to this rule has

been prepared. This analysis also contains the regulatory flexibility

determination required by the Regulatory Flexibility Act and a Trade

Impact Assessment. If more detailed economic information is desired,

the reader may refer to the full evaluation contained in the docket.

Benefits

Studies have shown that a significant PCF hazards exist in

rotorcraft operations. In a study of rotorcraft crashworthiness

dynamics, the FAA found that burn fatalities and injuries account for

about 14 percent of rotorcraft accident casualties and occur in about

20 percent of the accidents in which there are injuries. In a study

comparing rotorcraft equipped with and without a CRFS, the U.S. Army

found that average thermal casualty costs per survivable accident were

95.4 percent lower in CRFS-equipped rotorcraft, and that 50 percent of

all rotorcraft accidents with a PCF are survivable prior to the onset

of fire. An FAA review of NTSB rotorcraft accident data from 1983

through 1987 shows that 295 accidents occurred that involved a crash

landing or collision with an object resulting in fatalities, serious

injuries, or combinations of fatalities and injuries. Sixty-three of

these accidents involved a PCF, in which about 77 percent of the

occupants were fatally injured, as compared to 42 percent of the

occupants in accidents not involving a PCF.

In the 63 accidents involving a PCF, there were 113 fatalities, 27

serious injuries, 5 minor injuries, and one noninjury. The FAA

estimates that the use of CRFS's would have altered these casualty

distributions to approximately the following: 83 fatalities, 31 serious

injuries, 24 minor injuries, and 8 noninjuries--a difference of 30

fewer fatalities with some of the fatalities being reduced to serious

injuries (4) and minor injuries (19).

In order to provide the public and government officials with a

benchmark comparison of the expected safety benefits of rulemaking

actions with estimated costs over an extended period of time, the FAA

currently uses a minimum value of $1.5 million to statistically

represent an avoided fatality. Serious injuries are estimated to have

an average cost of $640,000, and minor injuries are estimated to have

an average cost of $2,300. Applying these values to the calculated

differences yields benefits of about $42 million [(30 fewer fatalities

x $1.5 million) - (4 more serious injuries x $640,000) - (19 more

minor injuries x $2,300)]. The average benefit per accident involving

a PCF is approximately $670,000. Accounting for parts 27 and 29

separately, the average benefits are approximately $464,000 per part 27

rotorcraft accident involving a PCF and approximately $1,638,000 per

part 29 rotorcraft accident involving a PCF.

During the 5-year study period, an average of 5,450 part 27

rotorcraft and an average of 1,150 part 29 rotorcraft were in operation

in the United States. During this period, the annual probability of a

part 27 rotorcraft being involved in a serious survivable accident with

a PCF is estimated to be 1.903 x 10-3 ((52 accidents / 5,450

part 27 rotorcraft) / 5 years). The corresponding probability for part

29 rotorcraft is 1.913 x 10-3 ((11 accidents / 1,150 part 29

rotorcraft) / 5 years). Multiplying these probabilities by an estimated

benefits per accident with a PCF yields annual benefits of $885 per

part 27 rotorcraft and $3,134 per part 29 rotorcraft. Assuming 15-year

operating lives, these benefits when discounted equate to $3,103 per

part 27 rotorcraft and $10,985 per part 29 rotorcraft.

Costs

This rule will increase costs for both rotorcraft manufacturers and

operators. Manufacturers will incur increased development,

certification, and production costs; and operators (in addition to

absorbing these costs in higher rotorcraft acquisition costs) will

incur increased operating costs due to the additional weight of the

fuel system.

The FAA estimates the development and certification costs per new

rotorcraft certification will be $36,000. Most of these costs are for

testing, analysis, and documentation. The primary testing required by

the rule is a test of each fuel tank to show no loss of fuel under

specified crash conditions. This can be accomplished by a simple,

inexpensive drop test.

There will be increased production costs associated with fuel

tanks, fittings, and flexible fuel lines. The incremental cost of a

fuel tank meeting the requirements of the rule is estimated to be $30

per gallon of tank capacity. Part 27 rotorcraft are assumed to have 50-

gallon tanks that will cost $1,500 more as a result of this rule; part

29 rotorcraft are assumed to have 200-gallon tanks costing $6,000 more.

The FAA estimates that the cost per frangible, self-sealing fitting is

$60; that a typical part 27 rotorcraft will require 8 fittings,

totaling $480; and that a typical part 29 rotorcraft will require 10

fittings, totaling $600. Flexible fuel line sections are expected to

add about $100 to the cost of a fuel system for a part 27 rotorcraft

and about $150 for a part 29 rotorcraft. The estimated total

incremental production costs are $2,080 per part 27 rotorcraft and

$6,750 per part 29 rotorcraft.

The FAA estimates that the rule will increase the weight of a part

27 rotorcraft by 9.5 pounds and a part 29 rotorcraft by 33 pounds, and

that each extra pound of weight increases average annual fuel

consumption by 3.8 gallons per part 27 rotorcraft and 6.2 gallons per

part 29 rotorcraft. Applying fuel prices of $1.87 per gallon for part

27 rotorcraft and $1.78 for part 29 rotorcraft, the estimated increase

in average annual operating costs is $68 ($1.87 x 3.8 gals. x 9.5

lbs.) per part 27 rotorcraft and $364 ($1.78 x 6.2 gals. x 33 lbs.)

per part 29 rotorcraft.

Assuming 15 years operating lives, the total incremental

development, certification, production, and operating costs when

discounted are $1,426 per part 27 rotorcraft and $4,617 per part 29

rotorcraft.

Benefit/Costs Comparison

Benefits exceed costs for both parts 27 and 29 rotorcraft. The net

present value (discounted benefits minus discounted costs) is $1,677

per part 27 rotorcraft and $6,368 per part 29 rotorcraft. The rule will

be cost beneficial even if it is only 50 percent effective in

eliminating PCF fatalities and injuries.

Regulatory Flexibility Determination

The Regulatory Flexibility Act (RFA) of 1980 was enacted by

Congress to ensure that small entities are not unnecessarily or

disproportionately burdened by Government regulations. The RFA requires

a Regulatory Flexibility Analysis if a rule is expected to have a

``significant economic impact on a substantial number of small

entities.'' FAA Order 2100.14A, Regulatory Flexibility Criteria and

Guidance, prescribes standards for complying with RFA review

requirements in FAA rulemaking actions. The FAA does not expect the

rule to have a significant economic impact on a substantial number of

small manufacturers or operators.

Trade Impact Assessment

The rule will have no impact on trade for either U.S. firms doing

business in foreign markets or foreign firms doing business in the

United States. In the United States, foreign manufacturers must meet

U.S. requirements, and thus will gain no competitive advantage. In

foreign countries, U.S. manufacturers are not bound by parts 27 and 29

requirements and can choose whether or not to implement the provisions

of this rule on the basis of competitive and other considerations.

Also, the Joint Airworthiness Authority (JAA) and Transport Canada are

both in the process of adopting this rule.

Federalism Implications

The regulations herein do not have substantial direct effects on

the states, on the relationship between the national government and the

states, or on the distribution of power and responsibilities among the

various levels of government. Therefore, in accordance with Executive

Order 12612, it is determined that this amendment does not have

sufficient federalism implications to warrant the preparation of a

Federalism Assessment.

Conclusion

For the reasons discussed in the preamble and based on the findings

in the Regulatory Flexibility Determination and the Trade Impact

Assessment, the FAA has determined that these amendments are not major

under Executive Order 12866. In addition, the FAA certifies that these

amendments do not have a significant economic impact, positive or

negative, on a substantial number of small entities under the criteria

of the Regulatory Flexibility Act. These amendments are considered

nonsignificant under DOT Regulatory Policies and Procedures (44 FR

11034; February 26, 1979). A regulatory evaluation of the amendments,

including a Regulatory Determination and Trade Impact Analysis, has

been placed in the docket. A copy may be obtained by contacting the

Rules Docket (AGC-10), Docket No. 26392, 800 Independence Avenue, SW.,

Washington, D.C. 25890

List of Subjects in 14 CFR Parts 27 and 29

Air transportation, Aircraft, Aviation safety, Rotorcraft, Safety.

The Amendment

Accordingly, the Federal Aviation Administration amends 14 CFR pats

27 and 29 of the Federal Aviation Regulations as follows:

PART 27--AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT

1. The authority citation for part 27 continues to read as follows:

Authority: 49 U.S.C. 1344, 1354(a), 1355, 1421, 1423, 1425,

1428, 1429, 1430; and 49 U.S.C. 106(g).

2. Section 27.561 is amended by adding a new paragraph (d) to read

as follows:

Sec. 27.561 General.

* * * * *

(d) Any fuselage structure in the area of internal fuel tanks below

the passenger floor level must be designed to resist the following

ultimate inertial factors and loads and to protect the fuel tanks from

rupture when those loads are applied to that area:

(i) Upward--1.5g.

(ii) Forward--4.0g.

(iii) Sideward--2.0g.

(iv) Downward--4.0g.

3. A new Sec. 27.952 is added to read as follows:

Sec. 27.952 Fuel system crash resistance.

Unless other means acceptable to the Administrator are employed to

minimize the hazard of fuel fires to occupants following an otherwise

survivable impact (crash landing), the fuel systems must incorporate

the design features of this section. These systems must be shown to be

capable of sustaining the static and dynamic deceleration loads of this

section, considered as ultimate loads acting alone, measured at the

system component's center of gravity, without structural damage to

system components, fuel tanks, or their attachments that would leak

fuel to an ignition source.

(a) Drop test requirements. Each tank, or the most critical tank,

must be drop-tested as follows:

(1) The drop height must be at least 50 feet.

(2) The drop impact surface must be nondeforming.

(3) The tank must be filled with water to 80 percent of the normal,

full capacity.

(4) The tank must be enclosed in a surrounding structure

representative of the installation unless it can be established that

the surrounding structure is free of projections or other design

features likely to contribute to rupture of the tank.

(5) The tank must drop freely and impact in a horizontal position

10 deg..

(6) After the drop test, there must be no leakage.

(b) Fuel tank load factors. Except for fuel tanks located so that

tank rupture with fuel release to either significant ignition sources,

such as engines, heaters, and auxiliary power units, or occupants is

extremely remote, each fuel tank must be designed and installed to

retain its contents under the following ultimate inertial load factors,

acting alone.

(1) For fuel tanks in the cabin:

(i) Upward--4g.

(ii) Forward--16g.

(iii) Sideward--8g.

(iv) Downward--20g.

(2) For fuel tanks located above or behind the crew or passenger

compartment that, if loosened, could injure an occupant in an emergency

landing:

(i) Upward--1.5g.

(ii) Forward--8g.

(iii) Sideward--2g.

(iv) Downward--4g.

(3) For fuel tanks in other areas:

(i) Upward--1.5g.

(ii) Forward--4g.

(iii) Sideward--2g.

(iv) Downward--4g.

breakaway couplings must be installed unless hazardous relative motion

of fuel system components to each other or to local rotorcraft

structure is demonstrated to be extremely improbable or unless other

means are provided. The couplings or equivalent devices must be

installed at all fuel tank-to-fuel line connections, tank-to-tank

interconnects, and at other points in the fuel system where local

structural deformation could lead to the release of fuel.

(1) The design and construction of self-sealing breakaway couplings

must incorporate the following design features:

(i) The load necessary to separate a breakaway coupling must be

between 25 to 50 percent of the minimum ultimate failure load (ultimate

strength) of the weakest component in the fluid-carrying line. The

separation load must in no case be less than 300 pounds, regardless of

the size of the fluid line.

(ii) A breakaway coupling must separate whenever its ultimate load

(as defined in paragraph (c)(1)(i) of this section) is applied in the

failure modes most likely to occur.

(iii) All breakaway couplings must incorporate design provisions to

visually ascertain that the coupling is locked together (leak-free) and

is open during normal installation and service.

(iv) All breakaway couplings must incorporate design provisions to

prevent uncoupling or unintended closing due to operational shocks,

vibrations, or accelerations.

(v) No breakaway coupling design may allow the release of fuel once

the coupling has performed its intended function.

(2) All individual breakaway couplings, coupling fuel feed systems,

or equivalent means must be designed, tested, installed, and maintained

so that inadvertent fuel shutoff in flight is improbable in accordance

with Sec. 27.955(a) and must comply with the fatigue evaluation

requirements of Sec. 27.571 without leaking.

(3) Alternate, equivalent means to the use of breakaway couplings

must not create a survivable impact-induced load on the fuel line to

which it is installed greater than 25 to 50 percent of the ultimate

load (strength) of the weakest component in the line and must comply

with the fatigue requirements of Sec. 27.571 without leaking.

(d) Frangible or deformable structural attachments. Unless

hazardous relative motion of fuel tanks and fuel system components to

local rotorcraft structure is demonstrated to be extremely improbable

in an otherwise survivable impact, frangible or locally deformable

attachments of fuel tanks and fuel system components to local

rotorcraft structure must be used. The attachment of fuel tanks and

fuel system components to local rotorcraft structure, whether frangible

or locally deformable, must be designed such that its separation or

relative local deformation will occur without rupture or local tear-out

of the fuel tank or fuel system components that will cause fuel

leakage. The ultimate strength of frangible or deformable attachments

must be as follows:

(1) The load required to separate a frangible attachment from its

support structure, or deform a locally deformable attachment relative

to its support structure, must be between 25 and 50 percent of the

minimum ultimate load (ultimate strength) of the weakest component in

the attached system. In no case may the load be less than 300 pounds.

(2) A frangible or locally deformable attachment must separate or

locally deform as intended whenever its ultimate load (as defined in

paragraph (d)(1) of this section) is applied in the modes most likely

to occur.

(3) All frangible or locally deformable attachments must comply

with the fatigue requirements of Sec. 27.571.

(e) Separation of fuel and ignition sources. To provide maximum

crash resistance, fuel must be located as far as practicable from all

occupiable areas and from all potential ignition sources.

(f) Other basic mechanical design criteria. Fuel tanks, fuel lines,

electrical wires, and electrical devices must be designed, constructed,

and installed, as far as practicable, to be crash resistant.

(g) Rigid or semirigid fuel tanks. Rigid or semirigid fuel tank or

bladder walls must be impact and tear resistant.

4. Section 27.963 is amended by revising paragraph (f) and by

adding new paragraphs (g) and (h) to read as follows:

Sec. 27.963 Fuel tanks: general.

* * * * *

(f) Each fuel tank installed in personnel compartments must be

isolated by fume-proof and fuel-proof enclosures that are drained and

vented to the exterior of the rotorcraft. The design and construction

of the enclosures must provide necessary protection for the tank, must

be crash resistant during a survivable impact in accordance with

Sec. 27.952, and must be adequate to withstand loads and abrasions to

be expected in personnel compartments.

(g) Each flexible fuel tank bladder or liner must be approved or

shown to be suitable for the particular application and must be

puncture resistant. Puncture resistance must be shown by meeting the

TSO-C80, paragraph 16.0, requirements using a minimum puncture force of

370 pounds.

(h) Each integral fuel tank must have provisions for inspection and

repair of its interior.

5. A new Sec. 27.967 is added to read as follows:

Sec. 27.967 Fuel tank installation.

(a) Each fuel tank must be supported so that tank loads are not

concentrated on unsupported tank surfaces. In addition--

(1) There must be pads, if necessary, to prevent chafing between

each tank and its supports;

(2) The padding must be nonabsorbent or treated to prevent the

absorption of fuel;

(3) If flexible tank liners are used, they must be supported so

that it is not necessary for them to withstand fluid loads; and

(4) Each interior surface of tank compartments must be smooth and

free of projections that could cause wear of the liner unless--

(i) There are means for protection of the liner at those points; or

(ii) The construction of the liner itself provides such protection.

(b) Any spaces adjacent to tank surfaces must be adequately

ventilated to avoid accumulation of fuel or fumes in those spaces due

to minor leakage. If the tank is in a sealed compartment, ventilation

may be limited to drain holes that prevent clogging and excessive

pressure resulting from altitude changes. If flexible tank liners are

installed, the venting arrangement for the spaces between the liner and

its container must maintain the proper relationship to tank vent

pressures for any expected flight condition.

Sec. 27.1185 (a) and (c).

(d) No rotorcraft skin immediately adjacent to a major air outlet

from the engine compartment may act as the wall of the integral tank.

6. Section 27.973 is revised to read as follows:

Sec. 27.973 Fuel tank filler connection.

(a) Each fuel tank filler connection must prevent the entrance of

fuel into any part of the rotorcraft other than the tank itself during

normal operations and must be crash resistant during a survivable

impact in accordance with Sec. 27.952(c). In addition--

(1) Each filler must be marked as prescribed in Sec. 27.1557(c)(1);

(2) Each recessed filler connection that can retain any appreciable

quantity of fuel must have a drain that discharges clear of the entire

rotorcraft; and

(3) Each filler cap must provide a fuel-tight seal under the fluid

pressure expected in normal operation and in a survivable impact.

(b) Each filler cap or filler cap cover must warn when the cap is

not fully locked or seated on the filler connection.

7. Section 27.975 is amended by revising paragraph (b) to read as

follows:

Sec. 27.975 Fuel tank vents.

* * * * *

(b) The venting system must be designed to minimize spillage of

fuel through the vents to an ignition source in the event of a rollover

during landing, ground operation, or a survivable impact, unless a

rollover is shown to be extremely remote.

PART 29--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT

8. The authority citation for part 29 continues to read as follows:

Authority: 49 U.S.C. 1344, 1354(a), 1355, 1421, 1423, 1424,

1425, 1428, 1429, 1430; and 49 U.S.C. 106(g).

9. A new Sec. 29.952 is added to read as follows:

Sec. 29.952 Fuel system crash resistance.

Unless other means acceptable to the Administrator are employed to

minimize the hazard of fuel fires to occupants following an otherwise

survivable impact (crash landing), the fuel systems must incorporate

the design features of this section. These systems must be shown to be

capable of sustaining the static and dynamic deceleration loads of this

section, considered as ultimate loads acting alone, measured at the

system component's center of gravity without structural damage to the

system components, fuel tanks, or their attachments that would leak

fuel to an ignition source.

(a) Drop test requirements. Each tank, or the most critical tank,

must be drop-tested as follows:

(1) The drop height must be at least 50 feet.

(2) The drop impact surface must be nondeforming.

(3) The tanks must be filled with water to 80 percent of the

normal, full capacity.

(4) The tank must be enclosed in a surrounding structure

representative of the installation unless it can be established that

the surrounding structure is free of projections or other design

features likely to contribute to rupture of the tank.

(5) The tank must drop freely and impact in a horizontal position

10 deg..

(6) After the drop test, there must be no leakage.

(b) Fuel tank load factors. Except for fuel tanks located so that

tank rupture with fuel release to either significant ignition sources,

such as engines, heaters, and auxiliary power units, or occupants is

extremely remote, each fuel tank must be designed and installed to

retain its contents under the following ultimate inertial load factors,

acting alone.

(1) For fuel tanks in the cabin:

(i) Upward--4g.

(ii) Forward--16g.

(iii) Sideward--8g.

(iv) Downward--20g.

(2) For fuel tanks located above or behind the crew or passenger

compartment that, if loosened, could injure an occupant in an emergency

landing:

(i) Upward--1.5g.

(ii) Forward--8g.

(iii) Sideward--2g.

(iv) Downward--4g.

(3) For fuel tanks in other areas:

(i) Upward--1.5g.

(ii) Forward--4g.

(iii) Sideward--2g.

(iv) Downward--4g.

breakaway couplings must be installed unless hazardous relative motion

of fuel system components to each other or to local rotorcraft

structure is demonstrated to be extremely improbable or unless other

means are provided. The couplings or equivalent devices must be

installed at all fuel tank-to-fuel line connections, tank-to-tank

interconnects, and at other points in the fuel system where local

structural deformation could lead to the release of fuel.

(1) The design and construction of self-sealing breakaway couplings

must incorporate the following design features:

(i) The load necessary to separate a breakaway coupling must be

between 25 to 50 percent of the minimum ultimate failure load (ultimate

strength) of the weakest component in the fluid-carrying line. The

separation load must in no case be less than 300 pounds, regardless of

the size of the fluid line.

(ii) A breakaway coupling must separate whenever its ultimate load

(as defined in paragraph (c)(1)(i) of this section) is applied in the

failure modes most likely to occur.

(iii) All breakaway couplings must incorporate design provisions to

visually ascertain that the coupling is locked together (leak-free) and

is open during normal installation and service.

(iv) All breakaway couplings must incorporate design provisions to

prevent uncoupling or unintended closing due to operational shocks,

vibrations, or accelerations.

(v) No breakaway coupling design may allow the release of fuel once

the coupling has performed its intended function.

(2) All individual breakaway couplings, coupling fuel feed systems,

or equivalent means must be designed, tested, installed, and maintained

so inadvertent fuel shutoff in flight is improbable in accordance with

Sec. 29.955(a) and must comply with the fatigue evaluation requirements

of Sec. 29.571 without leaking.

(3) Alternate, equivalent means to the use of breakaway couplings

must not create a survivable impact-induced load on the fuel line to

which it is installed greater than 25 to 50 percent of the ultimate

load (strength) of the weakest component in the line and must comply

with the fatigue requirements of Sec. 29.571 without leaking.