[Federal Register Volume 59, Number 190 (Monday, October 3, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-24218]


[[Page Unknown]]

[Federal Register: October 3, 1994]


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Part IV





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



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14 CFR Parts 27 and 29




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

Federal Aviation Administration

14 CFR Parts 27 and 29

[Docket No. 26352 Amdts. 27-30, 29-35]
RIN 2120-AC68

 
Airworthiness Standards; Crash Resistant Fuel Systems in Normal 
and Transport Category Rotorcraft

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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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.
    (c) Fuel line self-sealing breakaway couplings. Self-sealing 
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.
    (c) The location of each tank must meet the requirements of 
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.
    (c) Fuel line self-sealing breakaway couplings. Self-sealing 
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.
    (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 component 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. 29.571.
    (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.
    10. Section 29.963 is amended by removing paragraph (b); by 
redesignating paragraphs (c), (d), and (e) as (b), (c), and (d) 
respectively; by revising redesignated paragraph (b); and by adding a 
new paragraph (e) to read as follows:


Sec. 29.963  Fuel tanks: general.

* * * * *
    (b) 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.
* * * * *
    (e) 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. 29.952, and must be adequate to withstand loads and abrasions to 
be expected in personnel compartments.


Sec. 29.967  [Amended]

    11. Section 29.967 is amended by removing paragraph (e).
    12. Section 29.973 is revised to read as follows:


Sec. 29.973  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. 29.952(c). In addition--
    (1) Each filler must be marked as prescribed in Sec. 29.1557(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.
    13. Section 29.975 is amended by revising paragraph (a)(7) to read 
as follows:


Sec. 29.975  Fuel tank vents and carburetor vapor vents.

    (a) * * *
    (7) 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 operations, or a survivable impact, unless a 
rollover is shown to be extremely remote.
* * * * *
    Issued in Washington, D.C., on September 26, 1994.
David R. Hinson,
Administrator.
[FR Doc. 94-24218 Filed 9-30-94; 8:45 am]
BILLING CODE 4910-13-M