[Federal Register Volume 79, Number 205 (Thursday, October 23, 2014)]
[Rules and Regulations]
[Pages 63300-63302]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2014-25239]
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. FAA-2014-0434; Special Conditions No. 25-544-SC]
Special Conditions: Bombardier Aerospace, Models BD-500-1A10 and
BD-500-1A11; Composite Wing and Fuel Tank Structure Post-Crash Fire
Survivability
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
-----------------------------------------------------------------------
SUMMARY: These special conditions are issued for the Bombardier
Aerospace, Models BD-500-1A10 and BD-500-1A11 series airplanes. These
airplanes will have novel or unusual design features when compared to
the state of technology envisioned in the airworthiness standards for
transport category airplanes. These design features are composite
materials used in the construction of the fuel tank skin and structure,
which may behave differently in a post-crash fire than traditional
aluminum construction. These 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.
DATES: Effective Date: This action is effective on November 24, 2014.
FOR FURTHER INFORMATION CONTACT: Alan Sinclair, FAA, Airframe and Cabin
Safety Branch, ANM-115 Transport Airplane Directorate, Aircraft
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-
3356; telephone 425-227-2195; facsimile 425-227-1232.
SUPPLEMENTARY INFORMATION:
Background
On December 10, 2009, Bombardier Aerospace applied for a type
certificate for their new Models BD-500-1A10 and BD-500-1A11 series
airplanes (hereafter collectively referred to as ``CSeries''). The
CSeries airplanes are swept-wing monoplanes with an aluminum alloy
fuselage sized for 5-abreast seating. Passenger capacity is designated
as 110 for the Model BD-500-1A10 and 125 for the Model BD-500-1A11.
Maximum takeoff weight is 131,000 pounds for the Model BD-500-1A10 and
144,000 pounds for the Model BD-500-1A11.
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. The CSeries airplanes will not be fabricated
primarily with aluminum for the fuel tank structure. Instead, they will
be fabricated using predominantly composite structure and skin for the
wings and fuel tanks. Composites may or may not have the equivalent
capability of 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 novel and unusual with respect to the designs envisioned
when the applicable regulations were promulgated, additional tests and
analyses substantiation will be required to show that the CSeries
airplanes will provide an acceptable level of safety with respect to
the performance of the wings and fuel tanks during an external fuel-fed
fire.
[[Page 63301]]
Type Certification Basis
Under the provisions of Title 14, Code of Federal Regulations (14
CFR) 21.17, Bombardier Aerospace must show that the CSeries airplanes
meet the applicable provisions of 14 CFR part 25 as amended by
Amendments 25-1 through 25-129.
If the Administrator finds that the applicable airworthiness
regulations (i.e., 14 CFR part 25) do not contain adequate or
appropriate safety standards for the CSeries airplanes because of a
novel or unusual design feature, special conditions are prescribed
under the provisions of Sec. 21.16.
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 Sec. 21.101.
In addition to the applicable airworthiness regulations and special
conditions, the CSeries airplanes must comply with the fuel vent and
exhaust emission requirements of 14 CFR part 34 and the noise
certification requirements of 14 CFR part 36, and the FAA must issue a
finding of regulatory adequacy under Sec. 611 of Public Law 92-574,
the ``Noise Control Act of 1972.''
The FAA issues special conditions, as defined in 14 CFR 11.19, in
accordance with Sec. 11.38, and they become part of the type-
certification basis under Sec. 21.17(a)(2).
Novel or Unusual Design Features
The CSeries airplanes will incorporate the following novel or
unusual design features: The structural elements and skin of the wings
and fuel tanks will be fabricated using predominantly composite
materials rather than conventional aluminum.
Discussion
Transport category airplanes in operation today have traditionally
been designed with aluminum materials. Conventional airplanes with
aluminum skin and structure provide a well-understood level of safety
during post-crash fires with respect to fuel tanks. Current regulations
were developed and have evolved under the assumption that wing
construction would be of aluminum materials.
Aluminum has the following properties with respect to fuel tanks
and fuel-fed external fires:
Aluminum is highly thermally conductive and 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 of fuel vapors prior to fuel tank skin
burn-through or heating of the wing upper surface above the auto-
ignition temperature, thus greatly reducing 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 14 CFR 1.1 and Advisory Circular (AC) 20-135,
Powerplant Installation and Propulsion System Component Fire Protection
Test Methods, Standards, and Criteria.
Heat absorption capacity of aluminum and fuel prevent
burn-through or wing collapse for a time interval that generally
exceeds the passenger evacuation time.
The ability of aluminum wing surfaces to withstand post-crash fire
conditions when wetted by fuel on their interior surface has been
demonstrated by tests conducted at the FAA Technical Center. Results of
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 and
significantly delay 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.
Fuel tanks constructed with composite materials may or may not have
equivalent properties. AC 20-107B (Change 1), Composite Aircraft
Structure, section 11b, ``Fire Protection, Flammability and Thermal
Issues,'' states: ``Wing and fuselage applications should consider the
effects of composite design and construction on the resulting passenger
safety in the event of in-flight fires or emergency landing conditions,
which combine with subsequent egress when a fuel-fed fire is
possible.'' Pertinent to the wing structure, 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 and
also as a result of over-pressurization caused by ignition of fuel
vapors in the fuel tank.
For the CSeries airplanes, composite materials will be used to
fabricate the majority of the wing fuel tank. Hence, the current
regulations may not be adequate for the certification of the CSeries
airplanes featuring wing fuel tanks fabricated with composite material.
Therefore, Bombardier must present additional confirmation by test and
analysis that the CSeries airplanes' design provides an acceptable
level of safety with respect to the performance of the wing fuel tanks
when exposed to the direct effects of post-crash ground fire or under-
wing fuel-fed fires.
These 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.
Discussion of Comments
Notice of proposed special conditions No. 25-14-08-SC for the
Bombardier CSeries airplanes was published in the Federal Register on
July 16, 2014 (79 FR 41457). No comments were received, and the special
conditions are adopted as proposed.
Applicability
As discussed above, these special conditions are applicable to the
Models BD-500-1A10 and BD-500-1A11 series airplanes. Should Bombardier
Aerospace apply at a later date for a change to the type certificate to
include another model incorporating the same novel or unusual design
feature, the special conditions would apply to that model as well.
Conclusion
This action affects only certain novel or unusual design features
on two model series of airplanes. It is not a rule of general
applicability.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
0
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Special Conditions
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special conditions are issued as part of
the type certification basis for Bombardier Aerospace Models BD-500-
1A10 and BD-500-1A11 series airplanes.
[[Page 63302]]
Composite Wing and Fuel Tank Post-Crash Fire Survivability
1. The wing fuel tank structure must withstand an external fuel-fed
pool fire for a minimum of 5 minutes.
2. The integrity of the wing fuel tank structure must be
demonstrated at:
Minimum fuel load, not less than reserve fuel level;
Maximum fuel load equal to the maximum range fuel
quantity; and
Any other critical fuel loads.
3. The demonstration must consider fuel tank flammability, burn-
through resistance, wing structural strength retention properties, and
auto-ignition threats from localized heating of composite structure,
fasteners, or any other feature that may produce an ignition source
during a ground fire event for the required time duration.
Issued in Renton, Washington, on October 16, 2014.
Michael Kascycki,
Acting Manager, Transport Airplane Directorate.
[FR Doc. 2014-25239 Filed 10-22-14; 8:45 am]
BILLING CODE 4910-13-P