This section of the FEDERAL REGISTER

contains notices to the public of the proposed

issuance of rules and regulations. The

purpose of these notices is to give interested

persons an opportunity to participate in the

rule making prior to the adoption of the final

rules.

Proposed Rules Federal Register

1334 

Vol. 79, No. 5 

Wednesday, January 8, 2014 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

Docket No. FAA–2013–0908; Notice No. 

25–13–24–SC] 

Special Conditions: Airbus, Model 

A350–900 Series Airplane; Airplane 

Level of Safety Provided by Composite 

Fuel Tank Structure: Post-Crash Fire 

Survivability. 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of proposed special 

conditions. 

SUMMARY: This action proposes special 

conditions for Airbus Model A350–900 

series airplanes. These airplanes will 

have a novel or unusual design 

feature(s) associated with the post-crash 

fire survivability of composite fuel 

tanks. The applicable airworthiness 

regulations do not contain adequate or 

appropriate safety standards for this 

design feature. 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. 

DATES: Send your comments on or 

before February 24, 2014. 

ADDRESSES: Send comments identified 

by docket number FAA–2013–0908 

using any of the following methods: 

• Federal eRegulations Portal: Go to 

http://www.regulations.gov/ and follow 

the online instructions for sending your 

comments electronically. 

• Mail: Send comments to Docket 

Operations, M–30, U.S. Department of 

Transportation (DOT), 1200 New Jersey 

Avenue SE., Room W12–140, West 

Building Ground Floor, Washington, 

DC, 20590–0001. 

• Hand Delivery or Courier: Take 

comments to Docket Operations in 

Room W12–140 of the West Building 

Ground Floor at 1200 New Jersey 

Avenue SE., Washington, DC, between 8 

a.m. and 5 p.m., Monday through 

Friday, except federal holidays. 

• Fax: Fax comments to Docket 

Operations at 202–493–2251. 

Privacy: The FAA will post all 

comments it receives, without change, 

to http://www.regulations.gov/, 

including any personal information the 

commenter provides. Using the search 

function of the docket Web site, anyone 

can find and read the electronic form of 

all comments received into any FAA 

docket, including the name of the 

individual sending the comment (or 

signing the comment for an association, 

business, labor union, etc.). DOT’s 

complete Privacy Act Statement can be 

found in the Federal Register published 

on April 11, 2000 (65 FR 19477–19478), 

as well as at http://DocketsInfo. 

dot.gov/. 

Docket: Background documents or 

comments received may be read at http: 

//www.regulations.gov/ at any time. 

Follow the online instructions for 

accessing the docket or go to the Docket 

Operations in Room W12–140 of the 

West Building Ground Floor at 1200 

New Jersey Avenue SE., Washington, 

DC, between 9 a.m. and 5 p.m., Monday 

through Friday, except federal holidays. 

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: 

Comments Invited 

We invite interested people to take 

part in this rulemaking by sending 

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 will consider all comments we 

receive on or before the closing date for 

comments. We may change these 

proposed special conditions based on 

the comments we receive. 

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 June 28, 2009. The 

Model A350–900 series airplane has a 

conventional layout with twin wingmounted 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 will 

accommodate 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. Airbus proposes the Model A350– 

900 series airplane to be certified for 

extended operations (ETOPS) beyond 

180 minutes at entry into service for up 

to a 420-minute maximum diversion 

time. 

The Model A350–900 series airplane 

will be the second large transport 

category airplane certificated with 

composite wing and fuel tank structure 

that may be exposed to the direct effects 

of post-crash ground or under-wing fuelfed fires. Although the FAA has 

previously approved fuel tanks made of 

composite materials located in the 

horizontal stabilizer of some airplanes, 

the composite wing structure of the 

Model A350–900 series airplane will 

incorporate 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.’’ 

Pertinent to the wing structure, postcrash 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 internal to the 

fuel tank. 

The inherent capability of aluminum 

to resist fire has been considered by the 

FAA in development of the current 

regulations. Title 14 Code of Federal 

Regulations (14 CFR) part 25 Chapter 1, 

Section 1.1, General Definitions, defines 

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Federal Register / Vol. 79, No. 5 / Wednesday, January 8, 2014 / Proposed Rules 1335 

1Hill, R., and Johnson, G.R., ‘‘Investigation of 

Aircraft Fuel Tank Explosions and Nitrogen Inerting 

Requirements During Ground Fires,’’ FAA Report 

DOT/FAA/RD–75–119, October 1975. Available via 

the FAA Technical Center Web site for Fire Safety 

at http://www.fire.tc.faa.gov/. 

fire resistant as follows: ‘‘With respect 

to sheet or structural members means 

the capacity to withstand the heat 

associated with fire at least as well as 

aluminum alloy in dimensions 

appropriate for the purpose for which 

they are used.’’ It is noteworthy that 

aluminum alloy is identified as the 

performance standard for fire resistance, 

though no thickness or heat intensities 

are defined. Based on the performance 

of aluminum alloy, the definition of fire 

resistance was later defined for testing 

of other materials in AC 20–135 as the 

capability to withstand a 2000° F flame 

for five minutes. 

The FAA has historically promulgated 

rules with the assumption that the 

material of construction for wing and 

fuselage would be aluminum. As a 

representative case, § 25.963 was 

promulgated as a result of a large fuelfed fire following the failures of fuel 

tank access doors caused by 

uncontained engine failures. During the 

subsequent Aviation Rulemaking 

Advisory Committee (ARAC) 

harmonization process, the structures 

group attempted to harmonize § 25.963 

regarding the impact and fire resistance 

of the fuel tank access panels. 

Discussions between the FAA and the 

European Aviation Safety Agency 

(EASA), formerly the European Joint 

Aviation Authorities (JAA), ensued 

regarding the need for fire resistance of 

the fuel tank access panels. The EASA 

position was that the FAA requirement 

for the access panels to be fire resistant 

when the surrounding wing structure 

was not required to be fire resistant was 

inconsistent and that the access panels 

only needed to be as fire resistant as the 

surrounding tank structure. The FAA 

position stated that the fuel tank access 

panel fire resistance requirement should 

be retained, and that long term there 

should be a minimum requirement 

created for the wing skin itself. Both 

authorities recognized that existing 

aluminum wing structure provided an 

acceptable level of safety. Further 

rulemaking has not yet been pursued. 

As with previous Airbus 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 William J. 

Hughes Technical Center.1

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. 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. 

Due to the inherent properties 

provided by aluminum skin and 

structure, current regulations may not 

be adequate as they were developed and 

have evolved under the assumption that 

wing construction would be of 

aluminum materials. Inherent properties 

of aluminum with respect to fuel tanks 

and fuel fed fires are as follows: 

• 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 prior to 

burn-through of the fuel tank skin 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 14 part 1 and AC 20–135. 

• 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. 

Type Certification Basis 

Under Title 14, Code of Federal 

Regulations (14 CFR) 21.17, Airbus must 

show that the Model A350–900 series 

airplane meets 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 Model A350–900 series airplane 

because of a novel or unusual design 

feature, special conditions are 

prescribed under § 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 proposed 

special conditions would also apply to 

the other model under § 21.101. 

The FAA issues special conditions, as 

defined in 14 CFR 11.19, under § 11.38, 

and they become part of the typecertification basis under § 21.17(a)(2). 

In addition to the applicable 

airworthiness regulations and special 

conditions, the Model A350–900 series 

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 § 611 of Public Law 92– 

574, the ‘‘Noise Control Act of 1972.’’ 

Novel or Unusual Design Features 

The Airbus Model A350–900 series 

airplane will incorporate the following 

novel or unusual design features: 

composite fuel tanks. 

Discussion 

The extensive use of composite 

materials in the design of the A350 wing 

and fuel tank structure is considered a 

major change from conventional and 

traditional methods of construction, as 

this will be only the second 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 postcrash fire safety performance of wing 

and fuel tank skin or structure. 

In order to provide the same level of 

safety as exists with conventional 

airplane construction, Airbus must 

demonstrate that the Model A350–900 

series airplane has sufficient post-crash 

survivability to enable occupants to 

safely evacuate in the event that the 

wings are exposed to a large fuel-fed 

fire. Factors in fuel tank survivability 

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1336 Federal Register / Vol. 79, No. 5 / Wednesday, January 8, 2014 / Proposed Rules 

2Cherry, R. and Warren, K. ‘‘Fuselage 

Burnthrough Protection for Increased Postcrash 

Occupant Survivability: Safety Benefit Analysis 

Based on Past Accidents, ‘‘FAA Report DOT/FAA/ 

AR–99/57, September 1999 and R G W Cherry & 

Associates Limited, ‘‘A Benefit Analysis for Cabin 

Water Spray Systems and Enhanced Fuselage 

Burnthrough Protection,’’ FAA Report DOT/FAA/

AR–02/49, April 7, 2003. 

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 burn-through 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.2

There is little benefit in requiring the 

design to prevent wing skin burnthrough beyond five minutes, due to the 

effects of the fuel fire itself on the rest 

of the airplane. 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, AC 20–135 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 

Model A350–900 series airplane fuel 

tanks must be capable of resisting a 

post-crash fire for at least 5 minutes. In 

demonstrating compliance, Airbus 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 apply to Airbus 

Model A350–900 series airplanes. 

Should Airbus apply later for a change 

to the type certificate to include another 

model incorporating the same novel or 

unusual design feature, the proposed 

special conditions would apply to that 

model as well under the provisions of 

§ 21.101. 

Conclusion 

This action affects only certain novel 

or unusual design features on the 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 Proposed Special Conditions 

Accordingly, pursuant to the 

authority delegated to me by the 

Administrator, the following special 

conditions are proposed as part of the 

type certification basis for the Model 

A350–900 series airplane: 

In addition to complying with 14 CFR 

part 25 regulations governing the firesafety performance of the fuel tanks, 

wings, and nacelle, the Airbus Model 

A350–900 series airplane must 

demonstrate acceptable post-crash 

survivability in the event the wings are 

exposed to a large fuel-fed ground fire. 

Airbus must demonstrate that the wing 

and fuel tank design can endure an 

external fuel-fed pool fire for at least 

five 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, burnthrough resistance, wing structural 

strength retention properties, and autoignition threats during a ground fire 

event for the required time duration. 

Issued in Renton, Washington, on October 

22, 2013. 

Stephen P. Boyd 

Acting Manager, Transport Airplane 

Directorate, Aircraft Certification Service. 

[FR Doc. 2014–00102 Filed 1–7–14; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. FAA–2013–0901; Notice 

No. 25–13–23–SC] 

Special Conditions: Airbus, Model 

A350–900 Series Airplane; Flight 

Envelope Protection: High Speed 

Limiting 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of proposed special 

conditions. 

SUMMARY: This action proposes special 

conditions for Airbus Model A350–900 

series airplanes. These airplanes will 

have a novel or unusual design feature 

associated with high speed limiting. The 

applicable airworthiness regulations do 

not contain adequate or appropriate 

safety standards for this design feature. 

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. 

DATES: Send your comments on or 

before February 7, 2014. 

ADDRESSES: Send comments identified 

by docket number FAA–2013–0901 

using any of the following methods: 

• Federal eRegulations Portal: Go to 

http://www.regulations.gov/ and follow 

the online instructions for sending your 

comments electronically. 

• Mail: Send comments to Docket 

Operations, M–30, U.S. Department of 

Transportation (DOT), 1200 New Jersey 

Avenue SE., Room W12–140, West 

Building Ground Floor, Washington, DC 

20590–0001. 

• Hand Delivery or Courier: Take 

comments to Docket Operations in 

Room W12–140 of the West Building 

Ground Floor at 1200 New Jersey 

Avenue SE., Washington, DC., between 

9 a.m. and 5 p.m., Monday through 

Friday, except federal holidays. 

• Fax: Fax comments to Docket 

Operations at 202–493–2251. 

Privacy: The FAA will post all 

comments it receives, without change, 

to http://www.regulations.gov/, 

including any personal information the 

commenter provides. Using the search 

function of the docket Web site, anyone 

can find and read the electronic form of 

all comments received into any FAA 

docket, including the name of the 

individual sending the comment (or 

signing the comment for an association, 

business, labor union, etc.). DOT’s 

complete Privacy Act Statement can be 

found in the Federal Register published 

on April 11, 2000 (65 FR 19477–19478), 

as well as at http://DocketsInfo. 

dot.gov/. 

Docket: Background documents or 

comments received may be read at 

http://www.regulations.gov/ at any time. 

Follow the online instructions for 

accessing the docket or go to the Docket 

Operations in Room W12–140 of the 

West Building Ground Floor at 1200 

New Jersey Avenue SE., Washington, 

DC, between 9 a.m. and 5 p.m., Monday 

through Friday, except federal holidays. 

FOR FURTHER INFORMATION CONTACT: Joe 

Jacobsen, FAA, Airplane and Flightcrew 

Interface Branch, ANM–111, Transport 

Airplane Directorate, Aircraft 

Certification Service, 1601 Lind Avenue 

SW., Renton, Washington 98057–3356; 

telephone (425) 227–2011; facsimile 

(425) 227–1320. 

SUPPLEMENTARY INFORMATION: 

Comments Invited 

We invite interested people to take 

part in this rulemaking by sending 

mstockstill on DSK4VPTVN1PROD with PROPOSALS