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contains regulatory documents having general

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are keyed to and codified in the Code of

Federal Regulations, which is published under

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Rules and Regulations Federal Register

46167 

Vol. 79, No. 152 

Thursday, August 7, 2014 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. FAA–2013–0907; Special 

Conditions No. 25–541–SC] 

Special Conditions: Airbus Model 

A350–900 Series Airplane; Tire 

Failure—Debris Penetration or Rupture 

of Fuel-Tank Structure 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Final special conditions. 

SUMMARY: These special conditions are 

issued for Airbus Model A350–900 

series airplanes. These airplanes will 

have a novel or unusual design feature 

associated with fuel tanks constructed 

of carbon-fiber reinforced plastic (CFRP) 

materials located within the tire-impact 

zone, including the wing fuel tanks. 

The ability of aluminum wing skins, 

as has been conventionally used, to 

resist penetration or rupture when 

impacted by tire debris, is understood 

from extensive experience. The ability 

of carbon-fiber composite material to 

resist these hazards has not been 

established. No current airworthiness 

standards specifically address this 

hazard for all exposed wing surfaces. 

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: September 8, 

2014. 

FOR FURTHER INFORMATION CONTACT: 

Doug Bryant, Propulsion/Mechanical 

Systems, ANM–112, Transport Airplane 

Directorate, Aircraft Certification 

Service, 1601 Lind Avenue SW., 

Renton, Washington, 98057–3356; 

telephone (425) 227–2384; facsimile 

(425) 227–1320. 

SUPPLEMENTARY INFORMATION: 

Background 

On August 25, 2008, Airbus applied 

for a type certificate for their new Model 

A350–900 series airplane. Later, Airbus 

requested and the FAA approved an 

extension to the application for FAA 

type certification to November 15, 2009. 

The Model A350–900 series airplane 

has a conventional layout with twin 

wing-mounted Rolls-Royce Trent XWB 

engines. It features a twin aisle, 9- 

abreast, economy-class layout, and 

accommodates side-by-side placement 

of LD–3 containers in the cargo 

compartment. The basic Model A350– 

900 series airplane configuration 

accommodates 315 passengers in a 

standard two-class arrangement. The 

design cruise speed is Mach 0.85 with 

a maximum take-off weight of 602,000 

lbs. 

Accidents have resulted from 

uncontrolled fires caused by fuel leaks 

following penetration or rupture of the 

lower wing by fragments of tires, or 

from uncontained engine failure. In a 

November 1984 accident, a Boeing 

Model 747 airplane tire burst during an 

aborted takeoff from Honolulu, Hawaii. 

That tire debris penetrated a fuel-tank 

access cover, causing substantial fuel 

leakage. Passengers were evacuated 

down the emergency slides into pools of 

fuel that fortunately had not ignited. 

After an August 1985 Boeing Model 

737 airplane accident in Manchester, 

England, in which a fuel-tank access 

cover was penetrated by engine debris 

creating a fire, the FAA amended Title 

14, Code of Federal Regulations (14 

CFR) 25.963 to require fuel-tank access 

covers that are resistant to both tire and 

engine debris (engine debris is 

addressed outside of these special 

conditions). Modifications to the access 

covers were required of the existing fleet 

by an amendment to 14 CFR part 121. 

This regulation, § 25.963(e), only 

addressed the fuel-tank access covers 

because service experience at the time 

showed that the lower-wing skin of a 

conventional, subsonic airplane 

provided adequate inherent capability 

to resist tire and engine debris threats. 

More specifically, this regulation 

requires showing, by analysis or tests, 

that the access covers ‘‘. . . minimize 

penetration and deformation by tire 

fragments, low energy engine debris, or 

other likely debris.’’ Advisory Circular 

(AC) 25.963–1 defines the region of the 

wing that is vulnerable to impact 

damage from these sources and provides 

a method to substantiate that the rule 

has been met for tire fragments. No 

specific requirements were established 

for the contiguous wing areas into 

which the access covers are installed. 

AC 25.963–1 specifically notes, ‘‘The 

access covers, however, need not be 

more impact resistant than the 

contiguous tank structure,’’ highlighting 

the assumption that the wing was 

adequately addressed. 

The Concorde accident in July 2000 is 

the most notable example. That accident 

demonstrated an unanticipated failure 

mode in an airplane with an unusual 

transport-airplane configuration. Impact 

to the thin aluminum wing surface by 

tire debris induced pressure waves 

within the fuel tank that resulted in fuel 

leakage and fire. The skin on the 

Concorde delta-wing supersonic 

airplane is made of aluminum, having a 

thickness that is much less than that of 

a conventional subsonic airplane. 

Several previous accidents from burst 

tires damaged the fuel tank and wings 

on the Concorde. In 1979, a burst maingear tire put a hole through the wing, 

causing both fuel and hydraulic leaks. 

In 1980, a burst tire damaged the engine 

and airframe. In July 1993, a main-gear 

tire burst, damaging the wing and 

causing hydraulic problems. In October 

1993, a main-gear tire burst, broke the 

water deflector, and created holes in the 

fuel tank. Fortunately, the fuel did not 

catch fire during any of these events 

before the July 2000 accident involving 

the Concorde airplane. 

Following the accident in 2000, 

regulatory authorities required 

modifications to the Concorde aircraft to 

improve impact resistance of the lower 

wing, or means to retain fuel if the 

primary fuel retention means is 

damaged. 

These accidents and incidents 

highlight the need to establish standards 

for fuel-tank designs and configurations 

that were not envisioned when the 

existing standards in 14 CFR part 25 

were issued. 

Type Certification Basis 

Under 14 CFR 21.17, Airbus must 

show that the Model A350–900 series 

airplane meets the applicable provisions 

of part 25, as amended by Amendments 

25–1 through 25–129. 


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46168 Federal Register / Vol. 79, No. 152 / Thursday, August 7, 2014 / Rules and Regulations 

If the Administrator finds that the 

applicable airworthiness regulations 

(i.e., 14 CFR part 25) do not contain 

adequate or appropriate safety standards 

for Model A350–900 series airplanes 

because of a novel or unusual design 

feature, special conditions are 

prescribed under the provisions of 

§ 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 § 21.101. 

In addition to the applicable 

airworthiness regulations and special 

conditions, the Model A350–900 series 

airplane must be shown to comply with 

the fuel-vent and exhaust-emission 

requirements of 14 CFR part 34, and the 

noise-certification requirements of 14 

CFR part 36. The FAA must issue a 

finding of regulatory adequacy under 

section 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 § 11.38, and they become part of 

the type-certification basis under 

§ 21.17(a)(2). 

Novel or Unusual Design Features 

The Airbus Model A350–900 series 

airplanes will incorporate the following 

novel or unusual design features: CFRP 

materials for most of the wing fuel-tank 

structure. 

Discussion 

To maintain the level of safety 

prescribed by § 25.963(e) for fuel-tank 

access covers, these special conditions 

establish a standard for resistance to 

potential tire-debris impacts to the 

contiguous wing surfaces, and require 

consideration of possible secondary 

effects of a tire impact, such as the 

induced pressure wave that was a factor 

in the Concorde accident. These special 

conditions take into account that new 

construction methods and materials 

may not necessarily provide the 

resistance to debris impact that has 

historically been shown as adequate. 

These special conditions are based on 

the defined tire-impact areas and tirefragment characteristics described in AC 

25.963–1. 

In addition, despite practical-design 

considerations, some uncommon debris 

larger than that defined in paragraph (b) 

may cause a fuel leak within the defined 

area, so paragraph (c) of these special 

conditions also takes into consideration 

possible leakage paths. Fuel-tank 

surfaces of typical transport airplanes 

have thick aluminum construction in 

the tire-debris impact areas that is 

tolerant to tire debris larger than that 

defined in paragraph (b) of these special 

conditions. Consideration of leaks 

caused by larger tire fragments is 

needed to ensure that an adequate level 

of safety is provided. 

Note: While § 25.963 includes 

consideration of uncontained engine debris, 

the effects of engine debris are not included 

in these special conditions because these 

related potential hazards are addressed on 

the Model A350–900 series airplane under 

the existing requirements of § 25.903(d). 

Section 25.903(d) requires minimizing the 

hazards from uncontained engine debris. 

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. 25–13–19–SC for the Airbus Model 

A350–900 series airplanes was 

published in the Federal Register on 

January 14, 2014 (79 FR 2388). No 

comments were received, and the 

special conditions are adopted as 

proposed. 

Applicability 

As discussed above, these special 

conditions are applicable to Airbus 

Model A350–900 series airplanes. 

Should Airbus 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 Airbus 

Model A350–900 series airplanes. It is 

not a rule of general applicability. 

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 Special Conditions 

Accordingly, pursuant to the 

authority delegated to me by the 

Administrator, the following special 

conditions are issued as part of the typecertification basis for Airbus Model 

A350–900 series airplanes. 

a. Impacts by tire debris to any fuel 

tank or fuel-system component located 

within 30 degrees to either side of wheel 

rotational planes may not result in 

penetration or otherwise induce fueltank deformation, rupture (for example, 

through propagation of pressure waves), 

or cracking sufficient to allow a 

hazardous fuel leak. A hazardous fuel 

leak results if debris impact to a fuel 

tank surface causes— 

1. a running leak, 

2. a dripping leak, or 

3. a leak that, 15 minutes after wiping 

dry, results in a wetted airplane surface 

exceeding 6 inches in length or 

diameter. 

The leak must be evaluated under 

maximum fuel-head pressure. 

b. Compliance with paragraph (a) 

must be shown by analysis or tests 

assuming all of the following: 

1. The tire-debris fragment size is 

equal to 1 percent of the tire mass. 

2. The tire-debris fragment is 

propelled at a tangential speed that 

could be attained by a tire tread at the 

Airplane Flight Manual airplane 

rotational speed (VR at maximum gross 

weight). 

3. The tire-debris fragment load is 

distributed over an area on the fuel-tank 

surface equal to 1.5 percent of the total 

tire-tread area. 

c. Fuel leaks caused by impact from 

tire debris larger than that specified in 

paragraph (b), from any portion of a fuel 

tank or fuel-system component located 

within the tire-debris impact area 

defined in paragraph (a), may not result 

in hazardous quantities of fuel entering 

any of the following areas of the 

airplane: 

1. Engine inlet, 

2. APU inlet, or 

3. Cabin-air inlet. 

This must be shown by test or 

analysis, or a combination of both, for 

each approved engine forward-thrust 

condition, and each approved reversethrust condition. 

Jeffrey E. Duven, 

Manager, Transport Airplane Directorate, 

Aircraft Certification Service. 

[FR Doc. 2014–18653 Filed 8–6–14; 8:45 am] 

BILLING CODE 4910–13–P 


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