Special Conditions: Boeing Model 787-8 Airplane; Composite Wing and Fuel Tank Structure-Fire Protection Requirements, 17441-17443 [E7-6542]
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Federal Register / Vol. 72, No. 67 / Monday, April 9, 2007 / Proposed Rules
a loophole that creates a security
vulnerability that could potentially
compromise public health and safety.
rwilkins on PROD1PC63 with PROPOSAL
The Proposed Amendments
The petitioner requests that 10 CFR
part 73 be amended to require that
licensees implement procedures to
ensure that: (1) When information
becomes known to a licensee about an
individual that would prevent that
individual from gaining unescorted
access to the protected area of a nuclear
power plant, the licensee will
implement measures to ensure the
individual does not enter the protected
area, whether escorted or not; and (2)
when sufficient information is not
available to a licensee about an
individual to determine whether the
criteria for unescorted access are
satisfied, the licensee will implement
measures to allow that individual to
enter the protected area only when
escorted at all times by an armed
member of the security force who
remains in periodic communication
with security supervision. In the case of
the first proposal, the petitioner believes
that when it is known that a person’s
trustworthiness and reliability do not
meet the prescribed standards identified
in § 73.56(b), access to protected areas,
either escorted or unescorted, should be
denied. In the case of the second
proposal, the petitioner recognizes that
it is impractical and burdensome to
conduct background investigations of
every person requiring access to a
protected area, noting persons may need
one-time access. With that in mind, the
petitioner proposes granting these
persons access to protected areas, but
only when escorted by an armed
member of the security force and only
when this armed member is in periodic
communication with security
supervision.
Conclusion
The petitioner believes that current
regulations create a security
vulnerability that could potentially
compromise public health and safety.
The petitioner believes that its proposed
amendments to 10 CFR part 73 will
address this vulnerability in current
regulations that enables persons who do
not meet trustworthiness and reliability
standards for unescorted access to
protected areas of nuclear power plants
permission to enter protected areas with
an unarmed escort. Accordingly, the
petitioner requests that the NRC amend
its regulations related to the physical
protection of nuclear power plants and
materials as described previously in the
section titled, ‘‘The Proposed
Amendments.’’
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17:56 Apr 06, 2007
Jkt 211001
Dated at Rockville, Maryland, this 3rd day
of April 2007.
Kenneth R. Hart,
Acting Secretary of the Commission.
[FR Doc. E7–6644 Filed 4–6–07; 8:45 am]
BILLING CODE 7590–01–P
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM366 Special Conditions No.
25–07–03–SC]
Special Conditions: Boeing Model 787–
8 Airplane; Composite Wing and Fuel
Tank Structure—Fire Protection
Requirements
Federal Aviation
Administration (FAA), DOT.
ACTION: Notice of proposed special
conditions.
AGENCY:
SUMMARY: This notice proposes special
conditions for the Boeing Model 787–8
airplane. This airplane will have novel
or unusual design features when
compared to the state of technology
envisioned in the airworthiness
standards for transport category
airplanes. These novel or unusual
design features are associated with
composite materials chosen for the
construction of the fuel tank skin and
structure. For these design features, the
applicable airworthiness regulations do
not contain adequate or appropriate
safety standards for wing and fuel tank
structure with respect to post-crash fire
safety. These proposed special
conditions contain the additional safety
standards that the Administrator
considers necessary to establish a level
of safety equivalent to that established
by the existing airworthiness standards.
Additional special conditions will be
issued for other novel or unusual design
features of the Boeing Model 787–8
airplanes.
Comments must be received on
or before May 24, 2007.
ADDRESSES: Comments on this proposal
may be mailed in duplicate to: Federal
Aviation Administration, Transport
Airplane Directorate, Attention: Rules
Docket (ANM–113), Docket No. NM366,
1601 Lind Avenue, SW., Renton,
Washington 98057–3356; or delivered in
duplicate to the Transport Airplane
Directorate at the above address. All
comments must be marked Docket No.
NM366. Comments may be inspected in
the Rules Docket weekdays, except
Federal holidays, between 7:30 a.m. and
4 p.m.
DATES:
PO 00000
Frm 00002
Fmt 4702
Sfmt 4702
17441
FOR FURTHER INFORMATION CONTACT:
Mike Dostert, FAA, Propulsion/
Mechanical Systems, ANM–112,
Transport Airplane Directorate, Aircraft
Certification Service, 1601 Lind
Avenue, SW., Renton, Washington
98057–3356; telephone (425) 227–2132;
facsimile (425) 227–1320.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites interested persons to
participate in this rulemaking by
submitting written comments, data, or
views. The most helpful comments
reference a specific portion of the
special conditions, explain the reason
for any recommended change, and
include supporting data. We ask that
you send us two copies of written
comments.
We will file in the docket all
comments we receive as well as a report
summarizing each substantive public
contact with FAA personnel concerning
these proposed special conditions. The
docket is available for public inspection
before and after the comment closing
date. If you wish to review the docket
in person, go to the address in the
ADDRESSES section of this notice
between 7:30 a.m. and 4 p.m., Monday
through Friday, except Federal holidays.
We will consider all comments we
receive on or before the closing date for
comments. We will consider comments
filed late if it is possible to do so
without incurring expense or delay. We
may change the proposed special
conditions based on comments we
receive.
If you want the FAA to acknowledge
receipt of your comments on this
proposal, include with your comments
a pre-addressed, stamped postcard on
which the docket number appears. We
will stamp the date on the postcard and
mail it back to you.
Background
On March 28, 2003, Boeing applied
for an FAA type certificate for its new
Boeing Model 787–8 passenger airplane.
The Boeing Model 787–8 airplane will
be an all-new, two-engine jet transport
airplane with a two-aisle cabin. The
maximum takeoff weight will be
476,000 pounds, with a maximum
passenger count of 381 passengers.
Type Certification Basis
Under provisions of 14 CFR 21.17,
Boeing must show that Boeing Model
787–8 airplanes (hereafter referred to as
‘‘the 787’’) meet the applicable
provisions of 14 CFR part 25, as
amended by Amendments 25–1 through
25–117, except §§ 25.809(a) and 25.812,
which will remain at Amendment 25–
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Federal Register / Vol. 72, No. 67 / Monday, April 9, 2007 / Proposed Rules
rwilkins on PROD1PC63 with PROPOSAL
115. If the Administrator finds that the
applicable airworthiness regulations do
not contain adequate or appropriate
safety standards for the 787 because of
a novel or unusual design feature,
special conditions are prescribed under
provisions of 14 CFR 21.16.
In addition to the applicable
airworthiness regulations and special
conditions, the 787 must comply with
the fuel vent and exhaust emission
requirements of 14 CFR part 34 and the
noise certification requirements of part
36. In addition, the FAA must issue a
finding of regulatory adequacy pursuant
to section 611 of Pub. L. 92–574, the
‘‘Noise Control Act of 1972.’’
Special conditions, as defined in
§ 11.19, are issued in accordance with
§ 11.38 and become part of the type
certification basis in accordance with
§ 21.17(a)(2).
Special conditions are initially
applicable to the model for which they
are issued. Should the type certificate
for that model be amended later to
include any other model that
incorporates the same or similar novel
or unusual design feature, the special
conditions would also apply to the other
model under the provisions of § 21.101.
Novel or Unusual Design Features
The 787 will incorporate a number of
novel or unusual design features.
Because of rapid improvements in
airplane technology, the applicable
airworthiness regulations do not contain
adequate or appropriate safety standards
for these design features. These
proposed special conditions for the 787
contain the additional safety standards
that the Administrator considers
necessary to establish a level of safety
equivalent to that established by the
existing airworthiness standards.
The 787 will be the first large
transport category airplane that will not
be fabricated primarily with aluminum
materials for the fuel tank structure.
Instead it will use predominantly
composite materials for the structural
elements and skin of the wings and fuel
tanks. Conventional airplanes with
aluminum skin and structure provide a
well understood level of safety during
post-crash fire scenarios with respect to
fuel tanks. This is based on service
history and extensive full-scale fire
testing. Composites may or may not
have capabilities equivalent to
aluminum, and current regulations do
not provide objective performance
requirements for wing and fuel tank
structure with respect to post-crash fire
safety. Because the use of composite
structure is new and novel compared to
the designs envisioned when the
applicable regulations were written,
VerDate Aug<31>2005
17:56 Apr 06, 2007
Jkt 211001
additional substantiation by test and
analysis will be required to show that
the 787 provides an acceptable level of
safety with respect to the performance
of the wings and fuel tanks during an
external fuel-fed fire.
Although the FAA has previously
approved fuel tanks made of composite
materials that are located in the
horizontal stabilizer of some airplanes,
the composite wing structure of the 787
will introduce a new fuel tank
construction into service. Advisory
Circular (AC) 20–107A, Composite
Aircraft Structure, under the topic of
flammability, states: ‘‘The existing
requirements for flammability and fire
protection of aircraft structure attempt
to minimize the hazard to the occupants
in the event ignition of flammable fluids
or vapors occurs. The use of composite
structure should not decrease this
existing level of safety.’’ The relevance
to the wing structure is that post-crash
fire passenger survivability is dependent
on the time available for passenger
evacuation prior to fuel tank breach or
structural failure. Structural failure can
be a result of degradation in loadcarrying capability in the upper or lower
wing surface caused by a fuel-fed
ground fire. Structural failure can also
be a result of over-pressurization caused
by ignition of fuel vapors in the fuel
tank.
The FAA has historically developed
rules with the assumption that the
material of construction for wing and
fuselage would be aluminum. As a
representative case, § 25.963 was
developed as a result of a large fuel-fed
fire following the failures of fuel tank
access doors caused by uncontained
engine failures. During the subsequent
Aviation Rulemaking Advisory
Committee (ARAC) harmonization
process with the JAA,1 the structures
group attempted to harmonize the
requirements of § 25.963 regarding the
impact and fire resistance of fuel tank
access panels. Both authorities
recognized that existing aluminum wing
structure provided an acceptable level
of safety. Further rulemaking has not yet
been pursued.
As with previous Boeing airplane
designs with under-wing mounted
engines, the wing tanks and center tanks
1 The JAA is the Joint Aviation Authority of
Europe and the JAR is its Joint Aviation
Requirements, the equivalent of our Federal
Aviation Regulations. In 2003, the European
Aviation Safety Agency (EASA) was formed, and
EASA is now the principal aviation regulatory
agency in Europe. We intend to work with EASA
to ensure that our rules are also harmonized with
its Certification Specifications (CS). But since these
efforts in developing harmonization of § 25.963
occurred before EASA was formed, it was the JAA
that was involved with them.
PO 00000
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Fmt 4702
Sfmt 4702
are located in proximity to the
passengers and near the engines. Past
experience indicates post crash
survivability is greatly influenced by the
size and intensity of any fire that occurs.
The ability of aluminum wing surfaces
wetted by fuel on their interior surface
to withstand post-crash fire conditions
has been demonstrated by tests
conducted at the FAA Technical Center.
These tests have verified adequate
dissipation of heat across wetted
aluminum fuel tank surfaces so that
localized hot spots do not occur, thus
minimizing the threat of explosion. This
inherent capability of aluminum to
dissipate heat also allows the wing
lower surface to retain its load carrying
characteristics during a fuel-fed ground
fire. It significantly delays wing collapse
or burn-through for a time interval that
usually exceeds evacuation times. In
addition, as an aluminum fuel tank is
heated with significant quantities of fuel
inside, fuel vapor accumulates in the
ullage space, exceeding the upper
flammability limit relatively quickly
and thus reducing the threat of a fuel
tank explosion prior to fuel tank burnthrough. Service history of conventional
aluminum airplanes has shown that fuel
tank explosions caused by ground fires
have been rare on airplanes configured
with flame arrestors in the fuel tank
vent lines. Fuel tanks constructed with
composite materials may or may not
have equivalent capability.
Current regulations were developed
and have evolved under the assumption
that wing construction would be of
aluminum materials, which provide
inherent properties. Current regulations
may not be adequate when applied to
airplanes constructed of different
materials. Aluminum has the following
properties with respect to fuel tanks and
fuel-fed external fires.
• Aluminum is highly thermally
conductive. It readily transmits the heat
of a fuel-fed external fire to fuel in the
tank. This has the benefit of rapidly
driving the fuel tank ullage to exceed
the upper flammability limit prior to
burn-through of the fuel tank skin or
heating of the wing upper surface above
the auto-ignition temperature. This
greatly reduces the threat of fuel tank
explosion.
• Aluminum panels at thicknesses
previously used in wing lower surfaces
of large transport category airplanes
have been fire resistant as defined in
CFR 14 part 1 and AC 20–135.
• The heat capacity of aluminum and
fuel will prevent burn-through or wing
collapse for a time interval that will
generally exceed the passenger
evacuation time.
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Federal Register / Vol. 72, No. 67 / Monday, April 9, 2007 / Proposed Rules
The extensive use of composite
materials in the design of the 787 wing
and fuel tank structure is considered a
major change from conventional and
traditional methods of construction.
This will be the first large transport
category airplane to be certificated with
this level of composite material for these
purposes. The applicable airworthiness
regulations do not contain specific
standards for post-crash fire safety
performance of wing and fuel tank skin
or structure.
Discussion of Proposed Special
Conditions
In order to provide the same level of
safety as exists with conventional
airplane construction, Boeing must
demonstrate that the 787 has sufficient
post-crash survivability, in the event
that the wings are exposed to a large
fuel-fed fire, to enable occupants to
safely evacuate. Factors in fuel tank
survivability are the structural integrity
of the wing and tank, flammability of
the tank, burnthrough resistance of the
wing skin, and the presence of autoignition threats during exposure to a
fire. The FAA assessed post crash
survival time during the adoption of
amendment 25–111 for fuselage
burnthrough protection. Studies
conducted by and on behalf of the FAA
indicated that, following a survivable
accident, prevention of fuselage burnthrough for approximately 5 minutes
can significantly enhance survivability.
( See report numbers DOT/FAA/AR–99/
57 and DOT/FAA/AR–02/49.) Beyond
five minutes, there is little benefit, due
to the effects of the fuel fire itself. That
assessment was carried out based on
accidents involving airplanes with
conventional fuel tanks, and
considering the ability of ground
personnel to rescue occupants. In
addition, AC20–135 indicates that,
when aluminum is used for fuel tanks,
the tank should withstand the effects of
fire for 5 minutes without failure.
Therefore, to be consistent with existing
capability and related requirements, the
787 fuel tanks must be capable of
resisting a post crash fire for at least 5
minutes. In demonstrating compliance,
Boeing must address a range of fuel
loads from minimum to maximum, as
well as any other critical fuel load.
rwilkins on PROD1PC63 with PROPOSAL
Applicability
As discussed above, these proposed
special conditions are applicable to the
787. Should Boeing apply at a later date
for a change to the type certificate to
include another model incorporating the
same novel or unusual design features,
these proposed special conditions
VerDate Aug<31>2005
17:56 Apr 06, 2007
Jkt 211001
17443
would apply to that model as well
under the provisions of § 21.101.
ACTION:
Conclusion
SUMMARY: We propose to adopt a new
airworthiness directive (AD) for the
products listed above. This proposed
AD results from mandatory continuing
airworthiness information (MCAI)
originated by an aviation authority of
another country to identify and correct
an unsafe condition on an aviation
product. The MCAI describes the unsafe
condition as:
This action affects only certain novel
or unusual design features of the 787. It
is not a rule of general applicability, and
it affects only the applicant that applied
to the FAA for approval of these features
on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting
and recordkeeping requirements.
The authority citation for these
Special Conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701,
44702, 44704.
The Proposed Special Conditions
Accordingly, the Administrator of the
Federal Aviation Administration (FAA)
proposes the following special
conditions as part of the type
certification basis for the Boeing Model
787–8 airplane.
In addition to complying with part 25
regulations governing the fire-safety
performance of the fuel tanks, wings, and
nacelle, the Boeing Model 787–8 must
demonstrate acceptable post-crash
survivability in the event the wings are
exposed to a large fuel-fed ground fire.
Boeing must demonstrate that the wing and
fuel tank design can endure an external fuelfed pool fire for at least 5 minutes. This shall
be demonstrated for minimum fuel loads (not
less than reserve fuel levels) and maximum
fuel loads (maximum range fuel quantities),
and other identified critical fuel loads.
Considerations shall include fuel tank
flammability, burn-through resistance, wing
structural strength retention properties, and
auto-ignition threats during a ground fire
event for the required time duration.
Issued in Renton, Washington, on March
30, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate,
Aircraft Certification Service.
[FR Doc. E7–6542 Filed 4–6–07; 8:45 am]
BILLING CODE 4910–13–P
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA–2007–27806; Directorate
Identifier 2006–NM–287–AD]
RIN 2120–AA64
Airworthiness Directives; Dassault
Model Mystere-Falcon 50 Airplanes
Federal Aviation
Administration (FAA), DOT.
AGENCY:
PO 00000
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Fmt 4702
Sfmt 4702
Notice of proposed rulemaking
(NPRM).
* * * discovery of interferences between
the power wire supplying the galley’s coffeemaker and the surrounding structure. These
interferences might, by chafing and
degrading the wire insulation, generate short
circuits between the wire and the aircraft
ground through the composite cabinet
structure, without activation of the Circuit
Breaker (C/B). Several hot spots may then be
created and generate a large amount of thick
smokes just behind the cockpit.
The proposed AD would require
actions that are intended to address the
unsafe condition described in the MCAI.
DATES: We must receive comments on
this proposed AD by May 9, 2007.
ADDRESSES: You may send comments by
any of the following methods:
• DOT Docket Web site: Go to
https://dms.dot.gov and follow the
instructions for sending your comments
electronically.
• Fax: (202) 493–2251.
• Mail: Docket Management Facility,
U.S. Department of Transportation, 400
Seventh Street, SW., Nassif Building,
Room PL–401, Washington, DC 20590–
0001.
• Hand Delivery: Room PL–401 on
the plaza level of the Nassif Building,
400 Seventh Street, SW., Washington,
DC, between 9 a.m. and 5 p.m., Monday
through Friday, except Federal holidays.
• Federal eRulemaking Portal: https://
www.regulations.gov. Follow the
instructions for submitting comments.
Examining the AD Docket
You may examine the AD docket on
the Internet at https://dms.dot.gov; or in
person at the Docket Management
Facility between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal
holidays. The AD docket contains this
proposed AD, the regulatory evaluation,
any comments received, and other
information. The street address for the
Docket Office (telephone (800) 647–
5227) is in the ADDRESSES section.
Comments will be available in the AD
docket shortly after receipt.
FOR FURTHER INFORMATION CONTACT: Tom
Rodriguez, Aerospace Engineer,
International Branch, ANM–116, FAA,
Transport Airplane Directorate, 1601
Lind Avenue, SW., Renton, Washington
E:\FR\FM\09APP1.SGM
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]]>Agencies
[Federal Register Volume 72, Number 67 (Monday, April 9, 2007)]
[Proposed Rules]
[Pages 17441-17443]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E7-6542]
=======================================================================
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM366 Special Conditions No. 25-07-03-SC]
Special Conditions: Boeing Model 787-8 Airplane; Composite Wing
and Fuel Tank Structure--Fire Protection Requirements
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed special conditions.
-----------------------------------------------------------------------
SUMMARY: This notice proposes special conditions for the Boeing Model
787-8 airplane. This airplane will have novel or unusual design
features when compared to the state of technology envisioned in the
airworthiness standards for transport category airplanes. These novel
or unusual design features are associated with composite materials
chosen for the construction of the fuel tank skin and structure. For
these design features, the applicable airworthiness regulations do not
contain adequate or appropriate safety standards for wing and fuel tank
structure with respect to post-crash fire safety. These proposed
special conditions contain the additional safety standards that the
Administrator considers necessary to establish a level of safety
equivalent to that established by the existing airworthiness standards.
Additional special conditions will be issued for other novel or unusual
design features of the Boeing Model 787-8 airplanes.
DATES: Comments must be received on or before May 24, 2007.
ADDRESSES: Comments on this proposal may be mailed in duplicate to:
Federal Aviation Administration, Transport Airplane Directorate,
Attention: Rules Docket (ANM-113), Docket No. NM366, 1601 Lind Avenue,
SW., Renton, Washington 98057-3356; or delivered in duplicate to the
Transport Airplane Directorate at the above address. All comments must
be marked Docket No. NM366. Comments may be inspected in the Rules
Docket weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.
FOR FURTHER INFORMATION CONTACT: Mike Dostert, FAA, Propulsion/
Mechanical Systems, ANM-112, Transport Airplane Directorate, Aircraft
Certification Service, 1601 Lind Avenue, SW., Renton, Washington 98057-
3356; telephone (425) 227-2132; facsimile (425) 227-1320.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites interested persons to participate in this
rulemaking by submitting written comments, data, or views. The most
helpful comments reference a specific portion of the special
conditions, explain the reason for any recommended change, and include
supporting data. We ask that you send us two copies of written
comments.
We will file in the docket all comments we receive as well as a
report summarizing each substantive public contact with FAA personnel
concerning these proposed special conditions. The docket is available
for public inspection before and after the comment closing date. If you
wish to review the docket in person, go to the address in the ADDRESSES
section of this notice between 7:30 a.m. and 4 p.m., Monday through
Friday, except Federal holidays.
We will consider all comments we receive on or before the closing
date for comments. We will consider comments filed late if it is
possible to do so without incurring expense or delay. We may change the
proposed special conditions based on comments we receive.
If you want the FAA to acknowledge receipt of your comments on this
proposal, include with your comments a pre-addressed, stamped postcard
on which the docket number appears. We will stamp the date on the
postcard and mail it back to you.
Background
On March 28, 2003, Boeing applied for an FAA type certificate for
its new Boeing Model 787-8 passenger airplane. The Boeing Model 787-8
airplane will be an all-new, two-engine jet transport airplane with a
two-aisle cabin. The maximum takeoff weight will be 476,000 pounds,
with a maximum passenger count of 381 passengers.
Type Certification Basis
Under provisions of 14 CFR 21.17, Boeing must show that Boeing
Model 787-8 airplanes (hereafter referred to as ``the 787'') meet the
applicable provisions of 14 CFR part 25, as amended by Amendments 25-1
through 25-117, except Sec. Sec. 25.809(a) and 25.812, which will
remain at Amendment 25-
[[Page 17442]]
115. If the Administrator finds that the applicable airworthiness
regulations do not contain adequate or appropriate safety standards for
the 787 because of a novel or unusual design feature, special
conditions are prescribed under provisions of 14 CFR 21.16.
In addition to the applicable airworthiness regulations and special
conditions, the 787 must comply with the fuel vent and exhaust emission
requirements of 14 CFR part 34 and the noise certification requirements
of part 36. In addition, the FAA must issue a finding of regulatory
adequacy pursuant to section 611 of Pub. L. 92-574, the ``Noise Control
Act of 1972.''
Special conditions, as defined in Sec. 11.19, are issued in
accordance with Sec. 11.38 and become part of the type certification
basis in accordance with Sec. 21.17(a)(2).
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same or similar
novel or unusual design feature, the special conditions would also
apply to the other model under the provisions of Sec. 21.101.
Novel or Unusual Design Features
The 787 will incorporate a number of novel or unusual design
features. Because of rapid improvements in airplane technology, the
applicable airworthiness regulations do not contain adequate or
appropriate safety standards for these design features. These proposed
special conditions for the 787 contain the additional safety standards
that the Administrator considers necessary to establish a level of
safety equivalent to that established by the existing airworthiness
standards.
The 787 will be the first large transport category airplane that
will not be fabricated primarily with aluminum materials for the fuel
tank structure. Instead it will use predominantly composite materials
for the structural elements and skin of the wings and fuel tanks.
Conventional airplanes with aluminum skin and structure provide a well
understood level of safety during post-crash fire scenarios with
respect to fuel tanks. This is based on service history and extensive
full-scale fire testing. Composites may or may not have capabilities
equivalent to aluminum, and current regulations do not provide
objective performance requirements for wing and fuel tank structure
with respect to post-crash fire safety. Because the use of composite
structure is new and novel compared to the designs envisioned when the
applicable regulations were written, additional substantiation by test
and analysis will be required to show that the 787 provides an
acceptable level of safety with respect to the performance of the wings
and fuel tanks during an external fuel-fed fire.
Although the FAA has previously approved fuel tanks made of
composite materials that are located in the horizontal stabilizer of
some airplanes, the composite wing structure of the 787 will introduce
a new fuel tank construction into service. Advisory Circular (AC) 20-
107A, Composite Aircraft Structure, under the topic of flammability,
states: ``The existing requirements for flammability and fire
protection of aircraft structure attempt to minimize the hazard to the
occupants in the event ignition of flammable fluids or vapors occurs.
The use of composite structure should not decrease this existing level
of safety.'' The relevance to the wing structure is that post-crash
fire passenger survivability is dependent on the time available for
passenger evacuation prior to fuel tank breach or structural failure.
Structural failure can be a result of degradation in load-carrying
capability in the upper or lower wing surface caused by a fuel-fed
ground fire. Structural failure can also be a result of over-
pressurization caused by ignition of fuel vapors in the fuel tank.
The FAA has historically developed rules with the assumption that
the material of construction for wing and fuselage would be aluminum.
As a representative case, Sec. 25.963 was developed as a result of a
large fuel-fed fire following the failures of fuel tank access doors
caused by uncontained engine failures. During the subsequent Aviation
Rulemaking Advisory Committee (ARAC) harmonization process with the
JAA,\1\ the structures group attempted to harmonize the requirements of
Sec. 25.963 regarding the impact and fire resistance of fuel tank
access panels. Both authorities recognized that existing aluminum wing
structure provided an acceptable level of safety. Further rulemaking
has not yet been pursued.
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\1\ The JAA is the Joint Aviation Authority of Europe and the
JAR is its Joint Aviation Requirements, the equivalent of our
Federal Aviation Regulations. In 2003, the European Aviation Safety
Agency (EASA) was formed, and EASA is now the principal aviation
regulatory agency in Europe. We intend to work with EASA to ensure
that our rules are also harmonized with its Certification
Specifications (CS). But since these efforts in developing
harmonization of Sec. 25.963 occurred before EASA was formed, it
was the JAA that was involved with them.
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As with previous Boeing airplane designs with under-wing mounted
engines, the wing tanks and center tanks are located in proximity to
the passengers and near the engines. Past experience indicates post
crash survivability is greatly influenced by the size and intensity of
any fire that occurs. The ability of aluminum wing surfaces wetted by
fuel on their interior surface to withstand post-crash fire conditions
has been demonstrated by tests conducted at the FAA Technical Center.
These tests have verified adequate dissipation of heat across wetted
aluminum fuel tank surfaces so that localized hot spots do not occur,
thus minimizing the threat of explosion. This inherent capability of
aluminum to dissipate heat also allows the wing lower surface to retain
its load carrying characteristics during a fuel-fed ground fire. It
significantly delays wing collapse or burn-through for a time interval
that usually exceeds evacuation times. In addition, as an aluminum fuel
tank is heated with significant quantities of fuel inside, fuel vapor
accumulates in the ullage space, exceeding the upper flammability limit
relatively quickly and thus reducing the threat of a fuel tank
explosion prior to fuel tank burn-through. Service history of
conventional aluminum airplanes has shown that fuel tank explosions
caused by ground fires have been rare on airplanes configured with
flame arrestors in the fuel tank vent lines. Fuel tanks constructed
with composite materials may or may not have equivalent capability.
Current regulations were developed and have evolved under the
assumption that wing construction would be of aluminum materials, which
provide inherent properties. Current regulations may not be adequate
when applied to airplanes constructed of different materials. Aluminum
has the following properties with respect to fuel tanks and fuel-fed
external fires.
Aluminum is highly thermally conductive. It readily
transmits the heat of a fuel-fed external fire to fuel in the tank.
This has the benefit of rapidly driving the fuel tank ullage to exceed
the upper flammability limit prior to burn-through of the fuel tank
skin or heating of the wing upper surface above the auto-ignition
temperature. This greatly reduces the threat of fuel tank explosion.
Aluminum panels at thicknesses previously used in wing
lower surfaces of large transport category airplanes have been fire
resistant as defined in CFR 14 part 1 and AC 20-135.
The heat capacity of aluminum and fuel will prevent burn-
through or wing collapse for a time interval that will generally exceed
the passenger evacuation time.
[[Page 17443]]
The extensive use of composite materials in the design of the 787
wing and fuel tank structure is considered a major change from
conventional and traditional methods of construction. This will be the
first large transport category airplane to be certificated with this
level of composite material for these purposes. The applicable
airworthiness regulations do not contain specific standards for post-
crash fire safety performance of wing and fuel tank skin or structure.
Discussion of Proposed Special Conditions
In order to provide the same level of safety as exists with
conventional airplane construction, Boeing must demonstrate that the
787 has sufficient post-crash survivability, in the event that the
wings are exposed to a large fuel-fed fire, to enable occupants to
safely evacuate. Factors in fuel tank survivability are the structural
integrity of the wing and tank, flammability of the tank, burnthrough
resistance of the wing skin, and the presence of auto-ignition threats
during exposure to a fire. The FAA assessed post crash survival time
during the adoption of amendment 25-111 for fuselage burnthrough
protection. Studies conducted by and on behalf of the FAA indicated
that, following a survivable accident, prevention of fuselage burn-
through for approximately 5 minutes can significantly enhance
survivability. ( See report numbers DOT/FAA/AR-99/57 and DOT/FAA/AR-02/
49.) Beyond five minutes, there is little benefit, due to the effects
of the fuel fire itself. That assessment was carried out based on
accidents involving airplanes with conventional fuel tanks, and
considering the ability of ground personnel to rescue occupants. In
addition, AC20-135 indicates that, when aluminum is used for fuel
tanks, the tank should withstand the effects of fire for 5 minutes
without failure. Therefore, to be consistent with existing capability
and related requirements, the 787 fuel tanks must be capable of
resisting a post crash fire for at least 5 minutes. In demonstrating
compliance, Boeing must address a range of fuel loads from minimum to
maximum, as well as any other critical fuel load.
Applicability
As discussed above, these proposed special conditions are
applicable to the 787. Should Boeing apply at a later date for a change
to the type certificate to include another model incorporating the same
novel or unusual design features, these proposed special conditions
would apply to that model as well under the provisions of Sec. 21.101.
Conclusion
This action affects only certain novel or unusual design features
of the 787. It is not a rule of general applicability, and it affects
only the applicant that applied to the FAA for approval of these
features on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
The authority citation for these Special Conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Proposed Special Conditions
Accordingly, the Administrator of the Federal Aviation
Administration (FAA) proposes the following special conditions as part
of the type certification basis for the Boeing Model 787-8 airplane.
In addition to complying with part 25 regulations governing the
fire-safety performance of the fuel tanks, wings, and nacelle, the
Boeing Model 787-8 must demonstrate acceptable post-crash
survivability in the event the wings are exposed to a large fuel-fed
ground fire. Boeing must demonstrate that the wing and fuel tank
design can endure an external fuel-fed pool fire for at least 5
minutes. This shall be demonstrated for minimum fuel loads (not less
than reserve fuel levels) and maximum fuel loads (maximum range fuel
quantities), and other identified critical fuel loads.
Considerations shall include fuel tank flammability, burn-through
resistance, wing structural strength retention properties, and auto-
ignition threats during a ground fire event for the required time
duration.
Issued in Renton, Washington, on March 30, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. E7-6542 Filed 4-6-07; 8:45 am]
BILLING CODE 4910-13-P
