[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