[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]
_______________________________________________________________________
Part IV
Department of Transportation
_______________________________________________________________________
Federal Aviation Administration
_______________________________________________________________________
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