70922 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Parts 25, 91, 121, 125, and 129 

[Docket No. FAA–2005–22997; Notice No. 

05–14] 

RIN 2120–A123 

Reduction of Fuel Tank Flammability in 

Transport Category Airplanes 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of proposed rulemaking 

(NPRM). 

SUMMARY: This NPRM proposes new 

rules that will require operators and 

manufacturers of transport-category 

airplanes to take steps that, in 

combination with other required 

actions, should greatly reduce the 

chances of a catastrophic fuel-tank 

explosion. The proposal follows seven 

years of intensive research by the FAA 

in collaboration with industry into 

promising technologies designed to 

make fuel tanks effectively inert, thus 

preventing electrical and other systems 

from igniting flammable vapors in the 

fuel tank ullage (vapor space). The 

result of that research is that fuel tank 

inerting, originally thought to be 

prohibitively expensive, can now be 

accomplished in a reasonably costeffective fashion and protect the public 

from future calamities which, we have 

concluded, are otherwise virtually 

certain to occur. The new rules, if 

adopted, would not actually direct the 

adoption of specific inerting technology 

either by manufacturers or operators but 

would establish a performance-based set 

of requirements that do not specifically 

direct the use of fuel-inerting but rather 

set acceptable levels of flammability 

exposure in tanks most prone to 

explosion or require the installation of 

an ignition mitigation means in an 

affected fuel tank. Technology now 

provides a variety of commercially 

feasible methods to accomplish these 

vital safety objectives. 

DATES: Send your comments on or 

before March 23, 2006. 

ADDRESSES: You may send comments, 

identified by Docket No. FAA–2005– 

22997, using any of the following 

methods: 

DOT Docket Web site: Go to http:// 

dms.dot.gov and follow the instructions 

for sending your comments 

electronically. 

Government-wide rulemaking Web 

site: Go to http://www.regulations.gov 

and follow the instructions for sending 

your comments electronically. 

Mail: Docket Management Facility; 

U.S. Department of Transportation, 400 

Seventh Street, SW., Nassif Building, 

Room PL–401, Washington, DC 20590– 

001. 

Fax: 1–202–493–2251. 

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. 

For more information on the 

rulemaking process, see the 

SUPPLEMENTARY INFORMATION section of 

this document. 

Privacy: We will post all comments 

we receive, without change, to http:// 

dms.dot.gov, including any personal 

information you provide. For more 

information, see the Privacy Act 

discussion in the SUPPLEMENTARY

INFORMATION section of this document. 

Docket: To read background 

documents or comments received, go to 

http://dms.dot.gov at any time or to 

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. 

FOR FURTHER INFORMATION CONTACT: 

Michael E. Dostert, FAA, Propulsion/ 

Mechanical Systems Branch (ANM– 

112), Transport Airplane Directorate, 

Aircraft Certification Service, 1601 Lind 

Avenue, SW., Renton, Washington 

98055–4056; telephone (425) 227–2132, 

facsimile (425) 227–1320; e-mail: 

mike.dostert@faa.gov. 

SUPPLEMENTARY INFORMATION: 

Comments Invited 

The FAA invites interested persons to 

participate in this rulemaking by 

submitting written comments, data, or 

views. We also invite comments relating 

to the economic, environmental, energy, 

or federalism impacts that might result 

from adopting the proposals in this 

document. The most helpful comments 

reference a specific portion of the 

proposal, 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 this proposed rulemaking. 

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 preamble 

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

through Friday, except Federal holidays. 

You may also review the docket using 

the Internet at the web address in the 

ADDRESSES section. Comments that you 

may consider to be of a sensitive 

security nature should not be sent to the 

docket management system. Send those 

comments to the FAA, Office of 

Rulemaking, ARM–1, 800 Independence 

Avenue, SW., Washington, DC 20591. 

Privacy Act: Using the search function 

of our docket Web site, anyone can find 

and read the comments received into 

any of our dockets, including the name 

of the individual sending the comment 

(or signing the comment on behalf of an 

association, business, labor union, etc.). 

You may review DOT’s complete 

Privacy Act Statement in the Federal 

Register published on April 11, 2000 

(65 FR 19477–78) or you may visit 

http://dms.dot.gov. Before acting on this 

proposal, 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 this proposal in 

light of the 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 to you. 

Availability of Rulemaking Documents 

You can get an electronic copy using 

the Internet by: 

(1) Searching the Department of 

Transportation’s electronic Docket 

Management System (DMS) web page 

(http://dms.dot.gov/search); 

(2) Visiting the Office of Rulemaking’s 

web page at http://www.faa.gov/avr/ 

arm/index.cfm; or 

(3) Accessing the Government 

Printing Office’s web page at http:// 

www.access.gpo.gov/su_docs/aces/ 

aces140.html. 

You can also get a copy by submitting 

a request to the Federal Aviation 

Administration, Office of Rulemaking, 

ARM–1, 800 Independence Avenue, 

SW., Washington, DC 20591, or by 

calling (202) 267–9680. Make sure to 

identify the docket number, notice 

number, or amendment number of this 

rulemaking. 

Table of Contents 

I. Executive Summary 

II. Background 

A. The Need for Safety Improvements in 

Fuel Tank Systems 

B. Fuel Properties 

C. National Transportation Safety Board 

(NTSB) Recommendations 

D. FAA Response 

III. Proposed Requirements Relating to Fuel 

Tank Flammability 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70923 

1None of the 17 explosions occurred on an 

airplane manufactured by Airbus, who, along with 

Boeing, would be most affected by this rulemaking. 

Although Airbus currently delivers more airplanes 

worldwide than Boeing, their cumulative fleet 

hours are still relatively small, at approximately 65 

million (approximately 9% of total fleet hours for 

all transport category airplanes). Based on the 

FAA’s projection of the likelihood of an explosion 

based on one accident every 60 million hours, there 

is a 40% chance that no Airbus accidents would 

have occurred to date. 

2Philippine Airlines 737 accident in 1990 and 

the Thai Airlines accident in 2001. 

A. Overview of the Proposal 

B. Ongoing Responsibility of Type 

Certificate Holders for Continued 

Airworthiness 

C. Applicability 

1. Manufacturers and Holders of Type 

Certificates, Supplemental Type 

Certificates and Field Approvals 

2. Airplanes 

3. Fuel Tanks 

4. Airplane Operators 

D. Proposed Requirements for 

Manufacturers and Holders of Type 

Certificates, Supplemental Type 

Certificates and Field Approvals 

1. New Airplane Designs 

2. Existing Airplane Designs 

3. Auxiliary Fuel Tanks 

4. Methods of Mitigating the Likelihood of 

a Fuel Tank Explosion 

a. Flammability Analysis Using the Monte 

Carlo Method 

b. Ignition Mitigation Means 

c. Flammability Reduction Means 

i. Accounting for System Reliability and 

Performance Issues 

ii. Warm Day Fleet Flammability Exposure 

iii. Reliability Reporting 

iv. Reliability Indication and Maintenance 

Access 

d. Service Instructions and Service 

Bulletins 

e. Critical Design Configuration Control 

Limitations (CDCCL) 

f. Compliance Planning 

i. Compliance Plan for Flammability 

Exposure Analysis 

ii. Compliance Plan for Design Changes 

and Service Instructions 

iii. Compliance Plan for Auxiliary Fuel 

Tanks 

g. Compliance Schedule 

E. Proposed Requirements for Airplane 

Operators 

1. Requirement to Install and Operate FRM, 

IMM or FIMM 

2. Authority to Operate with an Inoperative 

FRM, IMM or FIMM 

3. Compliance Schedule 

F. Additional Provisions 

1. Relationship of this Proposal to Aging 

Airplane Regulatory Initiatives 

2. FAA Advisory Material 

3. FAA Oversight Office 

4. Workplace Safety Issues 

IV. Rulemaking Analyses and Notices 

V. The Proposed Amendment 

I. Executive Summary 

Fuel tank explosions have been a 

constant threat with serious aviation 

safety implications for many years. 

Since 1960, some 17 airplanes have 

been destroyed as the result of a fuel 

tank explosion.1 Four fatal airplane 

accidents have been caused by fuel tank 

explosions just since 1989. Two of the 

more recent accidents—one involving a 

Boeing Model 747 (TWA Flight 800) off 

Long Island, New York in 1996 and the 

other, a Boeing Model 727 accident 

(Avianca Flight 203) in Bogota ́, 

Columbia in 1989—occurred during 

flight and led to catastrophic losses, 

including the deaths of 337 individuals. 

The two other recent explosions 

occurred on the ground but led to nine 

fatalities.2 Although it was determined 

that a terrorist’s bomb had caused the 

explosion of the center tank in the 

Bogota ́ accident, the NTSB determined 

the ‘‘bomb explosion did not 

compromise the structural integrity of 

the airplane; however, the explosion 

punctured the [center wing tank] and 

ignited the fuel-air vapors in the ullage, 

resulting in destruction of the airplane.’’

Investigations of the other three 

accidents failed to identify the ignition 

source that caused the explosion. But in 

each instance the weather was warm, 

with an outside air temperature over 80 

°F, the incident occurred during the 

initial (ground, takeoff or climb) phases 

of flight, and the explosion involved 

empty or nearly empty tanks that had 

been previously fueled. Additionally, 

investigators were able to conclude that 

the center wing fuel tank in all four 

airplanes contained flammable vapors 

in the ullage (that portion of the fuel 

tank not occupied by liquid fuel) when 

the fuel tanks exploded. While the 

proposed requirements are not intended 

to address terrorist initiated fuel tank 

explosions, a system designed to reduce 

the likelihood of a fuel tank fire, or 

mitigate the effects of a fire should one 

occur, would have prevented these four 

fuel tank explosions. 

A statistical evaluation of these 

accidents has led the FAA to project 

that nine more transport category 

airplanes will likely be destroyed by a 

fuel tank explosion in the next 50 years, 

unless remedial measures are taken. 

Although we cannot forecast precisely 

when these accidents would occur, 

computer modeling that has been an 

accurate predictor in the past indicates 

these events are virtually certain to 

occur. We believe at least eight of these 

explosions are preventable if we adopt 

a comprehensive safety regime to reduce 

both the incidence of ignition and the 

likelihood of an explosion following 

ignition. We have already taken steps 

through other regulatory actions to 

reduce the chances of ignition. Today’s 

proposal attempts to address the risk of 

an explosion by reducing the likelihood 

that fuel tank vapors cause an explosion 

when an ignition source is introduced 

into the tank. 

Since the introduction of turbine 

powered airplanes, the FAA has 

premised its fuel tank rules on the 

assumption that fuel tanks will always 

contain flammable vapors and thus the 

best way to prevent explosions is to 

eliminate ignition sources. Since 2001, 

we have imposed airworthiness 

requirements (including airworthiness 

directives or ‘‘ADs’’) directed at the 

elimination of fuel tank ignition 

sources. Although these measures—

particularly Special Federal Aviation 

Regulation 88 of 14 CFR part 21 (SFAR 

88), which requires the detection and 

correction of potential system failures 

that can cause ignition—should prevent 

some of the nine forecast explosions, 

review of the current designs of 

airplanes in the transport category of all 

major manufacturers has shown that 

unanticipated failures and maintenance 

errors will continue to generate 

unexpected ignition sources. We have 

concluded we are unlikely ever to 

identify and eradicate all possible 

sources of ignition. 

To ensure safety, therefore, we must 

also focus on the environment that 

permits combustion to occur in the first 

place. Technology now exists that can 

prevent ignition of flammable fuel 

vapors by reducing their oxygen 

concentration below the level that will 

support combustion. By thus making the 

vapors ‘‘inert,’’ we can significantly 

reduce the likelihood of an explosion 

when a fire source is introduced to the 

fuel tank. Prototype onboard fuel tank 

inerting systems have been successfully 

flight tested on Airbus A320, Boeing 

Model 747, and Model 737 airplanes. 

Boeing applied in 2002 for type 

certification of an inerting system for 

the Model 747 that it plans to install on 

all new production 747 aircraft. 

Because the chances of a fuel tank 

explosion naturally correlate with the 

exposure of the tank to flammable 

vapors, the proposed requirements 

would mitigate the effects of such 

exposure or limit such exposure to 

acceptable levels by mandating the 

installation of either a Flammability 

Reduction Means (FRM) or an Ignition 

Mitigation Means (IMM). In either case, 

the technology would have to adhere to 

performance and reliability standards 

that would be set by the FAA and 

contained in Appendices K and L to 

Title 14 Code of Federal Regulations 

(CFR) part 25. 

If adopted, this rulemaking would 

amend the existing airworthiness 

70924 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

3The phrase ‘‘normally emptied’’ refers to fuel 

tanks that contain a substantial vapor space during 

a significant portion of the airplane operating time. 

Tanks that are designed to be normally emptied 

have been installed in various locations including 

the center wing structure, horizontal stabilizers, 

wings and cargo compartments. Fuel loading and 

usage management practices on certain airplane 

models use the auxiliary fuel tanks for controlling 

the center of gravity. 

standards contained in 14 CFR 25.981 

so as to require all type certificate (TC) 

holders and their licensees to develop 

FRM or IMM for many large turbine 

powered transport category airplanes 

with high risk fuel tanks. We would also 

amend 14 CFR parts 91, 121, 125 and 

129 so as to require operators of these 

airplanes to incorporate the approved 

FRM or IMM and to keep them 

operational. We estimate that 

approximately 3,800 Airbus and Boeing 

airplanes operated in the United States 

would be affected. Fuel tank system 

designs in several pending typecertification applications, including the 

Airbus A380 and the Boeing Model 7E7, 

would also have to meet the proposed 

requirements. 

We acknowledge that the proposed 

requirements are costly and propose 

these steps only after spending several 

years, in cooperation with scientists and 

other experts from the affected industry, 

researching the most cost-effective ways 

to prevent fuel tank explosions. Those 

efforts have resulted in the development 

of fuel-inerting technology that is vastly 

cheaper than originally thought. 

The loss of a single, fully loaded large 

passenger aircraft in flight, such as a 

Boeing Model 747 or Airbus A380, 

moreover, would result in death and 

destruction causing societal loss of at 

least $1.2 billion based on prior 

calamities, and we project that the new 

rule would prevent four accidents of 

some type (for analytical purposes we 

assume the accidents would involve 

‘‘average’’ aircraft with ‘‘average’’

passenger loads) over 50 years. Such 

estimates of harm do not account for the 

intangible costs of a series of in-flight 

explosions (such as a loss of confidence 

in aviation) or the indirect costs (such 

as trip cancellations following these 

incidents). 

Our philosophy is to address aviation 

safety threats whenever practicable 

solutions are found, especially when 

dealing with intractable and 

catastrophic risks like fuel tank 

explosions that are virtually certain to 

occur. Thus, now that solutions are 

reasonably cost-effective, the 

Administrator has tentatively 

determined that it is necessary for safety 

and in the public’s best interest to adopt 

the requirements proposed today. This 

action is in response to an NTSB 

recommendation. 

II. Background 

A. The Need for Safety Improvements in 

Fuel Tank Systems 

Fuel tank explosions continue to 

occur despite many safety 

improvements over the last 40 years 

aimed at removing ignition sources from 

fuel tanks. Experience tells us that even 

with the latest and most comprehensive 

initiative, SFAR 88, we cannot 

adequately protect the public from fuel 

tank explosions absent measures 

designed to lessen the exposure of 

vulnerable tanks to highly flammable jet 

fuel vapors. Fortunately, by taking such 

steps now to complement ignitionsource reduction measures already 

taken, we are confident that fuel tank 

explosions in affected aircraft will be 

nearly eliminated. 

For a variety of reasons, SFAR 88, 

though a significant advancement in 

safety, will never provide a complete 

safeguard against fuel tank explosions; 

thus our analysis has assumed that 

SFAR 88 will not reduce the possibility 

of a fuel explosion occurring by more 

than 50 percent. To be sure, SFAR 88 

has resulted in several significant 

changes in fuel tank system design and 

maintenance, including (1) new features 

to prevent dry running of fuel pumps 

within the fuel tanks; (2) use of ground 

fault protection of fuel pump power 

supplies for pumps or wires exposed to 

the fuel tank ullage; (3) addition of 

electrical bonds on some components; 

(4) use of electrical energy limiters on 

wiring entering fuel tanks that are 

‘‘normally emptied’’ 3 and located 

within the fuselage contour; (5) 

electrical bond integrity checks; and (6) 

improved maintenance programs. These 

design improvements, however, do not 

and cannot address all sources of 

ignition (such as external ignition 

sources resulting from fire). 

Past experience, moreover, shows that 

it is not possible to pinpoint and remove 

every ignition source from a large, 

complex transport aircraft. For example, 

the FAA is aware of one case where a 

manufacturer had conducted an 

exhaustive design review to identify 

possible sources of arcing within the 

fuel tank after a fuel tank exploded due 

to lightning. The manufacturer 

identified several possible sources of the 

arcing, and the FAA issued ADs to 

correct these deficiencies. The same 

airplane design was then evaluated as a 

result of SFAR 88, and additional 

sources of lightning-induced ignition 

were identified. In another instance, a 

TC holder submitted a safety analysis to 

the FAA claiming that certain airplane 

models met existing system safety 

requirements of § 25.1309 and thus that 

the likelihood of an ignition source 

developing was extremely improbable 

(one in a billion flight hours). When the 

requirements of the SFAR 88 safety 

review and unsafe condition criteria 

were applied, however, approximately 

80 new unsafe conditions were found. 

These conditions will now be addressed 

by AD for those airplane models but, in 

retrospect, it was clear that the 

manufacturer’s claims were erroneous. 

The safety reviews have also 

identified the potential for system 

failures (or ‘‘failure modes’’) that cannot 

be eliminated as possible ignition 

sources at reasonable cost. For example, 

use of ground fault protection for fuel 

pump power supplies will protect the 

fuel pumps from shorts to ground (such 

as one might find from lightning), but 

will not protect the fuel pumps from 

shorts between the three power wires to 

the pump, commonly referred to as 

‘‘phase-to-phase shorts.’’ Currently there 

is no proven component available to 

address this failure mode. Combinations 

of failure modes are even more 

problematic. We could require 

installation of redundant bond paths to 

prevent the latent failure of a critical 

electrical bond, but doing so would be 

cost-prohibitive. 

Finally, human error creates 

continuing risk. Each attempt to fix an 

electrical system presents the possibility 

of an inadvertent introduction of a new 

ignition source. Maintenance oversights, 

such as the failure to properly install 

electrical bonds or improper installation 

or overhaul of components, compound 

the possibility of an ignition source 

developing. 

Carrier fuel carrying practices could 

impact the possibility of an explosion as 

well. If a carrier decides to carry only 

that fuel necessary to meet the FAA’s 

fuel reserve requirements, the likelihood 

of an explosion is greater than if it 

carries excess fuel. This potential exists 

because more ignition sources within 

the fuel tank are exposed to the ullage 

and because the fuel has insulating 

properties which keeps the fuel tank 

cooler. Thus, ‘‘tankering’’, or carrying 

excess fuel, could theoretically lower 

the risk of an explosion. Current fuel 

management practices, where excess 

fuel is carried only when cost beneficial 

to the carrier, are largely market driven 

because airlines try to minimize their 

fuel costs to the maximum extent 

possible. Both the FAA and industry 

explored mandatory refueling of center 

wing tanks after the NTSB suggested the 

FAA adopt an interim flammability 

reduction measure in 1996. We 

determined that the reduction in 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70925 

4Most transport category airplanes used in air 

carrier service are approved for operation at 

altitudes from sea level to 45,000 feet. 

5NTSB recommendations provided on page 309 

of NTSB Accident Report, ‘‘In-flight Breakup Over 

the Atlantic Ocean, TransWorld Airlines Flight 800 

Boeing 747–131, N93119 Near East Moriches, New 

York, July 17, 1996, Report number NTSB/AAR–00/ 

03, DCA96MA070, Adopted August 23, 2000. 

flammability exposure would not be 

significant and would not address the 

warm day flammability risk. Thus, 

while either reducing or increasing the 

amount of fuel carried in the center 

wing tank could theoretically have some 

impact on the risk of an explosion, the 

FAA does not believe that current fuel 

carrying practices are likely either to 

change significantly or to have a 

measurable impact on the overall risk of 

an explosion. We seek comment on this 

position. 

B. Fuel Properties 

Three conditions must be present in 

a fuel tank to support combustion and 

a fuel-tank explosion: Fuel vapor in the 

right amount, enough oxygen, and an 

ignition source. As discussed earlier, 

our regulatory efforts since pistonpowered aircraft evolved into the jet age 

have been focused almost exclusively 

on the last item, ignition sources. A 

basic assumption in this approach has 

been that the fuel tank would contain 

flammable vapors under a wide range of 

airplane operating conditions. The 

question is, what level of exposure is 

safe? 

Jet fuel vapors are flammable only in 

certain temperature and pressure ranges. 

The flammability temperature range of 

such vapors varies with the type and 

properties of the fuel, the ambient 

pressure in the tank, and the amount of 

dissolved oxygen released from the fuel 

into the tank. The amount of dissolved 

oxygen in a tank will also vary 

depending on the amount of vibration 

and sloshing of the fuel that occurs 

within the tank. The temperature range 

in which a flammable fuel vapor will 

form can vary with different batches of 

fuel even for a specific fuel type, but the 

threshold temperature for flammability 

decreases as the airplane gains altitude 

because of the corresponding decrease 

of internal tank air pressure. Thus, the 

higher the airplane is flying, the lower 

the ambient temperature required for a 

fuel tank to explode when an ignition 

source introduced. 

Jet A fuel is the most commonly used 

commercial jet fuel in the United States 

and is widely used in other parts of the 

world. At sea level and with no sloshing 

or vibration present, these fuels have 

flammability characteristics that make it 

unlikely that the fuel molecules present 

in the fuel vapor-air mixture will ignite 

when the temperature in the fuel tank 

is below approximately 100 °F. The 

vapor will ignite, however, once the fuel 

temperature reaches approximately 175 

°F, because of the increased 

concentration of fuel molecules at 

higher temperatures. At an altitude of 

30,000 feet, the flammability 

temperature range drops to 

approximately 60 to 120 °F.4 Use of Jet 

A or Jet A–1 fuel thus tends to limit the 

risk of high flammability to warmer 

days. 

Jet B (JP–4) is another fuel approved 

for use on most commercial transport 

category airplanes, although it is no 

longer used as a primary fuel for 

commercial transports. The 

flammability range of Jet B (JP–4) is 

about 15 to 75 °F at sea level and 20 to 

35 °F at 30,000 feet. Because the 

flammable temperature range of Jet B 

fuel is more within the range of typical 

air temperatures at those altitudes 

where the airplane is likely to be 

operated, airplane fuel tanks with Jet B 

fuel are flammable for a much larger 

portion of the flight. 

C. National Transportation Safety Board 

(NTSB) Recommendations 

The NTSB determined that the 

probable cause of the in-flight explosion 

on TWA Flight 800 was the ignition of 

the flammable fuel/air mixture in the 

center wing fuel tank. However, the 

source of ignition energy for the 

explosion could not be determined with 

certainty. The Board also faulted, as 

contributing to the accident, the FAA’s 

design and certification approach to 

transport-category airplanes, as it (1) 

concentrated solely on precluding all 

ignition sources, and (2) allowed heat 

sources to be located beneath the center 

wing fuel tank. 

In 1996, the NTSB issued 

recommendations to improve fuel tank 

safety. The NTSB recommended both 

eradicating ignition sources and 

reducing fuel tank flammability.5 In 

their accident report, the Board 

concluded that ‘‘a fuel tank design and 

certification philosophy that relies 

solely on the elimination of all ignition 

sources, while accepting the existence 

of fuel tank flammability, is 

fundamentally flawed because 

experience has demonstrated that all 

possible ignition sources cannot be 

determined and reliably eliminated.’’

D. FAA Response 

The FAA conducted ignitionprevention safety reviews following the 

1996 accident, which revealed many 

new single-component failure modes 

that could ignite fuel tanks. We 

continue to issue ADs that require 

design or maintenance actions to 

address these deficiencies. These safety 

reviews also identified combinations of 

failures that could result in an ignition 

source, but as these combinations were 

less likely to occur than single failures, 

we determined that it was not practical 

to address them in existing airplanes. 

The safety reviews also confirmed that 

unforeseen design and maintenance 

errors could create ignition sources. 

Recognizing the need to focus on 

flammability rather than just ignition, 

on April 3, 1997, the FAA published a 

notice in the Federal Register seeking 

comments on the 1996 NTSB 

recommendations on flammability 

exposure (62 FR 16014). That notice 

reviewed the service history of transport 

category airplane fuel tanks and the 

challenges underlying fuel-tank 

flammability reduction. Public comment 

indicated that more information was 

needed before we could begin a 

rulemaking on this safety issue. 

Given that control of flammable 

vapors was a new concept, we assigned 

two Aviation Rulemaking Advisory 

Committee (ARAC) working groups to 

study the issues and provide 

recommendations. (The ARAC consists 

of interested parties, including the 

public, and provides a process to advise 

us on the development of new 

regulations.) The first working group 

reviewed the practicality of requiring 

flammability reduction, evaluating 

many different flammability reduction 

methods. Upon the recommendation of 

the first working group, the second 

working group then focused exclusively 

on fuel tank inerting. 

On January 23, 1998, we published a 

notice in the Federal Register that 

established the Fuel Tank 

Harmonization Working Group as part 

of ARAC (63 FR 3614). This group was 

asked to recommend regulations on fuel 

tank flammability for both newly 

certificated and existing airplanes. The 

working group looked at fuel tank 

explosions that occurred after Jet A fuel 

had replaced Jet B fuel as the 

predominant type used on transport 

airplanes. The group examined the 

performance of two types of fuel tanks: 

the center wing fuel tanks located 

within the fuselage contour, and wing 

fuel tanks. Fuel tanks located in an 

aluminum wing are typically unheated 

and cool quickly when the wing 

surfaces are exposed to colder air during 

flight. Conversely, the center wing fuel 

tanks in certain airplanes have 

equipment underneath the tank 

radiating heat; in addition, with no 

surfaces exposed to outside air, the tank 

70926 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

cools much more slowly than a wing 

fuel tank. 

The working group concluded that the 

safety records of fuel tanks located in 

aluminum wings of airplanes fueled 

with Jet A type fuel were satisfactory. 

These tanks had an average 

flammability exposure (as calculated 

under a methodology contained in 

proposed Part 25, Appendix L) of 

approximately 2 to 6 percent. However, 

the group found that on some airplane 

fleets the center wing fuel tanks had an 

average flammability exposure ranging 

from 7 percent to a high of 30 percent, 

a dangerous level. 

The working group then evaluated 

many possible means of reducing or 

removing the hazards associated with 

explosive vapors in fuel tanks, such as 

fuel tank inerting, fuel tank cooling, fuel 

property alteration, fire suppression 

systems and polyurethane foam 

treatments. The ARAC sent the working 

group’s report to the FAA on July 23, 

1998 (Docket No. FAA–1998–4183, 

viewable on the U.S. Department of 

Transportation electronic Document 

Management System at http:// 

dms.dot.gov). 

The working group report concluded 

that flammability reduction was 

practical for new airplane designs, but 

impractical for current production 

designs or retrofit in the current fleet of 

transport category airplanes. The report 

recommended that the FAA begin 

rulemaking to add a requirement to 

§ 25.981, so that fuel tanks in new 

airplane designs would have an average 

flammability exposure of less than 7 

percent. The report also recommended 

requiring by regulation that each newly 

designed airplane incorporate means to 

mitigate the effects of an ignition of fuel 

vapors, such that any damage caused 

would not prevent continued safe flight 

and landing. The report reviewed 

various technical solutions, including 

control of heat transmission into fuel 

tanks, use of inerting systems, or 

ignition mitigation means like 

polyurethane foam. The report 

concluded that the best solution was 

likely to be control of heat transmission 

and suggested that the most practical 

means of control were (1) relocation of 

the air-conditioning equipment away 

from the fuel tanks; (2) ventilation of the 

air-conditioning bay to limit heating and 

cool fuel tanks; or (3) insulation of the 

tanks from heat. Nevertheless, the 

ARAC also recommended that we 

continue to evaluate the costeffectiveness of other means for 

reducing flammable vapors in the fuel 

tanks, such as ground-based inerting of 

fuel tanks. 

Based in part on the ARAC 

recommendations, we issued a rule 

entitled ‘‘Transport Airplane Fuel Tank 

System Design, and Maintenance and 

Inspection Requirements’’ in the 

Federal Register on May 7, 2001 (66 FR 

23085). The rule added current 

§ 25.981(c) which requires minimization 

of fuel tank flammability exposure in 

new type designs without setting a 

specific safety standard. Section 

25.981(c) thus states: 

(c) The fuel tank installation must include 

either—

(1) Means to minimize the development of 

flammable vapors in the fuel tanks (in the 

context of this rule, ‘‘minimize’’ means to 

incorporate practicable design methods to 

reduce the likelihood of flammable vapors); 

or 

(2) Means to mitigate the effects of an 

ignition of fuel vapors within fuel tanks such 

that no damage caused by an ignition will 

prevent continued safe flight and landing. 

Higher flammability tanks are 

typically located in the center wing box, 

in the horizontal stabilizer where little 

surface area is exposed to outside air, or 

in the cargo compartment. Our intent, as 

discussed in that rule’s preamble was to 

‘‘require that [such] fuel tanks are not 

heated, and cool at a rate equivalent to 

that of a wing tank in the transport 

airplane being evaluated.’’ We noted 

that, ‘‘This may require incorporating 

design features to reduce flammability, 

for example cooling and ventilation 

means, or inerting for fuel tanks located 

in the center wing box, horizontal 

stabilizer, or auxiliary fuel tanks located 

in the cargo compartment.’’ (Our 

reference to a wing tank was to a 

conventional subsonic airplane with 

aluminum wing tanks.) We also stated, 

‘‘At such time as the FAA has 

completed the necessary research and 

identified an appropriate definitive 

standard to address this issue, new 

rulemaking would be considered to 

revise the standard proposed in this 

rulemaking.’’

We then issued two Advisory 

Circulars, AC 25.981–1B, ‘‘Fuel Tank 

Ignition Source Prevention Guidelines,’’

and AC 25.981–2, ‘‘Fuel Tank 

Flammability Minimization.’’ These 

ACs described acceptable means of 

showing compliance with § 25.981(c). 

AC 25.981–2 specifically discussed the 

use of fuel tank inerting as a method of 

compliance with the flammability 

exposure requirements. To ‘‘inert’’ a fuel 

tank, as defined in AC 25.981–2, the 

percentage of oxygen in a fuel tank’s air 

should not exceed 10 percent. (Later 

research, discussed below, showed that 

containing oxygen concentrations to 12 

percent or less would inert a fuel tank.) 

After revising § 25.981, we began 

scientific research, hoping to gain a 

better understanding of the ignition 

properties of commercial aviation jet 

fuel vapors. We also explored new ideas 

for removing flammable fuel air 

mixtures from fuel tanks, as well as 

other methods for improving fuel tank 

safety. Initially, efforts to develop 

commercially viable ways to remove 

flammable fuel vapors from tanks failed. 

For example, to lower the danger of fuel 

tank explosions after post-crash ground 

fires, systems were considered that 

would ‘‘scrub’’ the vapor in the ullage—

ventilating the tank with air so as to 

prevent the build-up of flammable 

concentrations of fuel vapor. At the 

time, we found these systems to be 

impractical because of their weight, 

complexity, unreliability, and 

undesirable secondary effects on the 

environment. 

On the recommendation of the ARAC, 

we refocused our efforts on reducing 

fuel tank flammability through nitrogen 

inerting. Public comment on the 1997 

notice had suggested inerting was 

possible through adoption of a hollow 

fiber membrane technology, which 

separates oxygen from nitrogen in the 

atmosphere. (Air is made up of about 78 

percent nitrogen and 21 percent 

oxygen.) The hollow fiber membrane 

material uses the absorption difference 

between the nitrogen and oxygen 

molecules to separate nitrogen-enriched 

air from oxygen. The technology had 

been used for many years in nonaerospace applications, such as 

obtaining oxygen-enriched air for 

medical purposes and generating 

nitrogen-enriched air to preserve 

produce in transport. In airplane 

applications, nitrogen-enriched air 

could be produced when pressurized air 

is forced through a canister that 

contains the hollow fibers. The created 

nitrogen-enriched air is then directed, at 

appropriate concentrations, into the 

ullage of fuel tanks and displaces the 

normal fuel vapor/air mixture in the 

tank. Use of this technology allows 

nitrogen to be separated from the 

available pressurized air onboard the 

airplane, which eliminates the need to 

carry and store nitrogen in the airplane. 

Initially, we found that airplanes in 

the current transport category fleet were 

not designed with optimized air sources 

for creating nitrogen-enriched air. As a 

result, early designs required 

installation of an air compressor, adding 

significant weight and cost. Aware of 

the earlier system’s disadvantages, our 

researchers worked to address those 

issues. Earlier fuel tank inerting designs, 

primarily produced for military 

applications to prevent fuel tank 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70927 

6The Effectiveness of Ullage Nitrogen-Inerting 

Systems Against 30-mm High-Explosive Incendiary 

Projectiles, China Lake Naval Weapons Center, J. 

Hardy Tyson and John F Barnes, May 1991. 

7Auxiliary fuel tanks are installed subject to 

amended supplemental type certificates or field 

approvals. As such they are ‘‘aftermarket’’

installations not contemplated by the original 

manufacturer of the airplane. Auxiliary fuel tanks 

are installed to permit airplanes to fly for longer 

periods of time by increasing the amount of 

available fuel. While all auxiliary fuel tanks are 

normally emptied, some ‘‘normally emptied’’ tanks 

are included in the original type design, such as the 

center wing tank on the Boeing 747. 

8The airplane flammability exposure evaluation 

time begins when the airplane is prepared for flight 

(which commences upon the start of preparing the 

airplane for flight by turning on the auxiliary power 

unit/ground power, starting the environmental 

control systems, or taking other steps that begin the 

Continued 

explosions from battle damage, assumed 

a fuel tank was ‘‘inert’’ with a maximum 

of 9 percent oxygen content in the 

ullage. Achieving this level of 

concentration was not needed for 

transport category airplanes, as our 

research determined that a maximum 

oxygen content of 12 percent would be 

sufficient to protect airplanes from less 

powerful ignition sources typical of 

airplane system failures and 

malfunctions at sea level. Thus, our 

testing excluded turbulent flow flame 

propagation, or external fuel tank 

events, such as explosives and hostile 

fire. (The FAA test results are available 

in an FAA Technical Note: ‘‘Limiting 

Oxygen Concentrations Required to 

Inert Jet Fuel Vapors Existing at 

Reduced Fuel Tank Pressures’’ (DOT/ 

FAA/AR–TN02/79). See: http:// 

www.fire.tc.faa.gov/pdf/TN02-79.pdf.) 

Terrorist initiated accidents were also 

excluded from consideration in the 

earlier ARAC reports and the possible 

benefits in the regulatory evaluation 

within this notice. While the proposed 

FRM requirements are not intended to 

address terrorist initiated explosions, 

such as the Bogata 727 accident 

discussed earlier, inerting fuel tanks 

may provide other significant secondary 

safety benefits by addressing 

flammability exposure. Testing 

conducted by China Lake Naval 

Weapons Center 6 showed that inerting 

a fuel tank to 12 percent oxygen offers 

a high degree of protection from a fuel 

tank explosion when 30-millimeter high 

explosive incendiary projectiles shot 

into fuel tanks. The FAA invites 

comments related to the potential 

additional security benefits that may be 

achieved by imposing FRM. 

Based on our research, we identified 

a simplified inerting system that, using 

existing airplane pressurized air 

sources, could limit a fuel tank to the 12 

percent oxygen content level. This 

concept eliminated the need for an air 

compressor, thus reducing the size and 

complexity of the system. Our research 

determined that the method of 

distributing the nitrogen-enriched air to 

the fuel tank could also be simplified, 

which further reduced the system’s 

weight and installation cost. We now 

estimate that a simplified inerting 

system adequate to protect the center 

wing tank on airplanes in the existing 

fleet should weigh from 100 to 250 

pounds and cost from $140,000 to 

$225,000 to procure and install in 

existing airplanes, depending on fuel 

tank capacity. (More information on the 

costs of these systems is provided in the 

Preliminary Regulatory Evaluation.) 

The FAA has openly shared with 

industry information on the simplified 

inerting system design ever since it was 

first developed in May 2002. This 

design concept was adopted by Boeing 

when applying for a series of type 

certification and production approvals 

to incorporate a fuel inerting system 

using nitrogen air enrichment in all 

currently produced Boeing model 

airplanes. Thus, on November 15, 2002, 

Boeing applied for a change to TC No. 

A20WE to modify Boeing Model 747 

series airplanes to incorporate the 

system into its center wing fuel tanks. 

It has since applied for similar 

approvals for the Boeing Model 737 

series, Boeing Model 757 series, Boeing 

Model 767 series, and Boeing Model 777 

series airplanes. We published a request 

for and received public comments on a 

Notice of Proposed Special Conditions 

for flammability reduction on the 

Boeing Model 747 on December 9, 2003 

(68 FR 68563). Final Special Conditions 

No. 25–285–SC was issued on January 

24, 2005 (70 FR 7800; February 15, 

2005). 

III. Proposed Requirements Relating to 

Fuel Tank Flammability 

We are proposing today a 

performance-based set of requirements 

that do not specifically direct the use of 

fuel inerting, but rather set acceptable 

levels of flammability exposure in tanks 

most prone to explosion or require the 

installation of an ignition mitigation 

means in an affected fuel tank. We also 

by separate notice propose to revise 

Advisory Circular 25.981–2 so as to 

describe several means of compliance 

with these requirements, including both 

flammability-reduction means, such as 

cooling, inerting using nitrogen or 

carbon dioxide, and ignition-mitigation 

means, such as use of polyurethane 

foam or explosion suppression systems. 

The revised AC sets out detailed 

parameters for such systems if used as 

a means of achieving the targeted safety 

standards. 

The rule, if adopted, would require a 

retrofit of much of the existing fleet of 

large airplanes but would not 

necessarily affect all transport aircraft. 

We will require retrofit based on safety 

needs, using a fleet average flammability 

exposure limit of seven (7) percent, the 

level recommended by ARAC. We know 

that this level is routinely exceeded in 

tanks that are incidentally heated by 

nearby air conditioning equipment and 

in unpressurized auxiliary fuel tanks 

that are located in the cargo 

compartment and that do not 

significantly cool. The vast majority of 

large transport category airplanes 

operating in the U.S., including all 

Airbus models and most Boeing models, 

have center wing tanks that are above 

this level. We estimate that 3,800 

airplanes with flammability exposure 

level above 7 percent would be 

retrofitted if this rule is adopted. 

As is the case for new production 

airplanes, all airplanes currently 

equipped with a normally emptied or 

auxiliary fuel tanks that have a 

flammability level above 7 percent 

could not have center wing tanks that 

are flammable more than 3 percent on 

average and 3 percent on hot days. 

Lowering the flammability levels of 

these fuel tanks in the existing fleet and 

limiting the permissible level of 

flammability on new production 

airplanes would result in an overall 

reduction in the flammability potential 

of these airplanes of approximately 95 

percent. 

Some airplane models have center 

tanks with a fleet average flammability 

exposure level that does not exceed 7 

percent, including to the best of our 

information the Lockheed L–1011, and 

Boeing MD–11, DC10, MD80, and 

Boeing Model 727, and Fokker F28 

MK100. At this time we do not believe 

that these airplanes would need FRM or 

IMM for their center tanks, unless the 

certificate holder has also installed an 

auxiliary fuel tank that is found to be 

affected.7

A. Overview of the Proposal 

Our proposal would require 

manufacturers and operators of most 

large transport category airplanes to 

reduce the average flammability 

exposure in affected fleets to tolerable 

levels of risk. Fleet average flammability 

exposure represents the percent of flight 

time that fuel vapors in the ullage are 

flammable, calculated across a fleet of 

an airplane type operating over the 

range of actual or expected flights and 

based on a wide range of environmental 

conditions and fuel properties.8 This 

70928 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

initial preparation of the airplane), continues 

through the actual flight and landing, and ends 

when all payload has been unloaded and all 

passengers and crew have disembarked. 

9Rather than relying on the analysis already 

conducted pursuant to SFAR 88 and then simply 

regulating those airplanes with a demonstrated 

exposure level of 7 percent or greater, today’s 

proposal contemplates requiring a new exposure 

analysis. The existing analyses, while helpful in 

positing which airplanes are likely to be affected by 

a final rule, were derived from incomplete, and 

sometimes differing, assumptions. Appendix L 

would correct such inconsistencies by establishing 

a single methodology for calculating average 

flammability exposure. 

rulemaking is premised on our finding 

that fuel tanks whose fleet-wide average 

flammability exposure is more than 7 

percent have a ‘‘high flammability 

exposure,’’ which we consider unduly 

dangerous. This finding, in turn, is 

based on the reports and findings of the 

ARAC and our own risk assessment of 

the current transport category airplane 

fleet. 

Our proposal would modify current 

regulations in several important 

respects, affecting both manufacturers 

(TC holders and STC holders) and 

operators (air carriers). We would 

significantly expand the coverage of part 

25 by making manufacturers generally 

responsible for the development of 

service information and safety 

improvements (including design 

changes) where needed to ensure the 

continued airworthiness of previously 

certificated airplanes. This proposal 

would apply to holders of existing TCs, 

holders of STCs, applicants for changes 

to existing TCs, and certain other 

airplane manufacturers. We are 

proposing to specify the new 

requirements for these entities in a new 

subpart I to part 25, although we may 

decide to relocate these requirements at 

the time the final rule is issued to 

simplify harmonization efforts. 

As to fuel tank flammability 

specifically, manufacturers, including 

holders of listed airplane TCs and of 

auxiliary fuel tank STCs, would be 

required to conduct a flammability 

exposure analysis of their fuel tanks, 

unless they have already notified the 

FAA that they will utilize an ignition 

mitigation means instead. A new 

Appendix L to part 25 will regulate the 

conduct of these analyses.9 As 

discussed later in this document, the 

Appendix contains the method for 

calculating overall and warm day fuel 

tank flammability exposure values 

needed to show that the affected aircraft 

tanks comply with proposed limitations 

on flammability exposure levels, 

described below. 

Where the required analyses indicate 

that the fuel tank has an average 

flammability exposure level below 7 

percent, no changes would be required. 

However, for the other fuel tanks, 

manufacturers would be required to 

develop design modifications to support 

a retrofit of the airplane. Under today’s 

proposal, the average flammability 

exposure level of any affected wing tank 

would have to be reduced to no more 

than 7 percent. In addition, for any 

normally emptied fuel tank (including 

auxiliary fuel tanks) located in whole or 

in part in the fuselage, flammability 

exposure would have to be reduced to 

3 percent, both for the overall fleet 

average and for operations on warm 

days. 

For long-pending certification projects 

that have not received a type certificate 

from the FAA prior to the date of the 

final rule (where application was 

received by the FAA before June 6, 

2001, the effective date of 14 CFR 

25.981(c), applicants would be required 

to limit the flammability exposure of 

any wing tank to no more than 7 

percent. Any of those applicants whose 

proposals include any normally emptied 

or auxiliary fuel tank with a 

flammability exposure level that 

exceeds 7 percent would also have to 

meet the same flammability exposure 

requirements proposed for retrofit (i.e., 

3 percent), if any portion of the tank is 

located within the fuselage contour. 

Applicants for more recent certification 

projects (where application was 

received after June 6, 2001), and all 

applicants for a TC or STC submitted 

after the effective date of the final rule 

would need to meet the new 

requirements of that section set forth in 

today’s proposal. 

We would set more stringent safety 

levels for certain critically located fuel 

tanks in most new type designs, while 

maintaining the current, general 

standard under § 25.981 for all other 

fuel tanks. We expect that as a result of 

this rule the design of most normally 

emptied and auxiliary tanks located, in 

whole or in part, in the fuselage of 

transport-category airplanes would need 

to incorporate some form of FRM or 

IMM. Regulations in a new proposed 

Appendix K to Part 25 contain detailed 

specifications for all FRM, if they are 

used to meet the flammability exposure 

limitations. These additional 

requirements are designed to ensure the 

reliability of flammability-reduction 

means, reporting of performance metrics 

and warnings of possible hazards in and 

around fuel tanks. Specifications for 

IMM are detailed in the current AC–

25.981–2 and are not generally 

discussed in this document. 

Type certificate holders for specific 

airplane models with high flammability 

exposure fuel tanks would be required 

to develop design changes and service 

instructions to facilitate the adoption of 

IMM or FRM. Manufacturers of these 

airplanes would have to incorporate 

these design changes in airplanes 

produced in the future. In addition, 

these sections would require design 

approval holders (TC and STC holders) 

and applicants to develop airworthiness 

limitations to ensure that maintenance 

actions and future modifications do not 

increase flammability exposure above 

the limits in this proposal. These design 

approval holders would have to submit 

binding certification plans by a 

specified date, and these plans would be 

closely monitored by the holders’ FAA 

oversight offices to ensure timely 

progress. 

Lastly, the proposal requires affected 

operators to incorporate FRM or IMM 

where required for high-risk fuel tanks 

in their existing fleet of affected airplane 

models. Air carriers would also have to 

revise their maintenance and inspection 

programs to incorporate the 

airworthiness limitations developed 

under the other proposals. We also 

intend to establish strict retrofit 

deadlines, which are premised on 

prompt compliance by manufacturers 

with their certification plans. 

Table 1 summarizes the proposed 

regulatory changes that relate to fuel 

tank flammability safety. This table does 

not summarize the proposed regulatory 

changes that are common between this 

proposal and other aging airplane 

initiatives. Those changes are discussed 

in detail later. 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70929 

TABLE 1.—SUMMARY OF PROPOSED RULES

14 CFR Description of proposal Applies to 

25.1, 25.2 ............................. Expand applicability to current holders of TCs, STCs, 

and certain manufacturers.

Amend § 25.2 to make reference to the proposed subpart I. 

Applicants for TCs, and changes to those TCs for 

transport category airplanes. Manufacturers of certain 

airplane models. 

25.981 .................................. Revise paragraph (b) to specify limits on fuel tank flammability.

Add paragraph (c) to restate current option of providing 

ignition mitigation means (IMM). 

Applicants for future TCs and design changes to those 

certificates. 

Add paragraph (d) to include airworthiness limitation 

items (ALI) for IMM or Flammability Reduction Means 

(FRM), and move the existing ignition prevention ALI 

requirements into this paragraph. 

Subpart I 25.1801 ................ Defines the intent of the subpart .................................... TCs, and design changes to those TCs for transport 

category airplanes. Manufacturers of certain airplane 

models. 

25.1815 ................................ Require flammability exposure analysis of all fuel tanks 

within 150 days after effective date. If below 7 percent no flammability reduction required. Compliance 

with § 25.981(d) to define ALI required.

TC holders. 

If above 7 percent and in fuselage and normally 

emptied, must develop service instructions to meet 

§ 25.981(b), (c) and (d).

If above 7 percent and other tank type, must develop 

service instructions to incorporate IMM (meet 

§ 25.981(c), or reduce flammability to 7 percent). 

Large transport category passenger airplanes, with passenger capacity of 30 or more or a payload of 7500 

lbs or more (original TC or later increase). 

Specific compliance dates for each Boeing and Airbus 

airplane model. Other models within 24 months. 

25.1817 ................................ Require flammability exposure analysis of all fuel tanks 

installed under STC within 12 months after effective 

date.

Require impact assessment of fuel tanks installed by 

STCs, and (for pending and future applicants) other 

STCs affecting fuel tank flammability, on IMM or 

FRM developed by TC holder under § 25.1815 to determine if any ALI has been violated 6 months after 

FAA approval of ALI submitted by TC holders under 

§ 25.1815 or before certification, whichever is later. 

Auxiliary tank STC holders for large transport category 

passenger airplanes, with passenger capacity of 30 

or more or a payload of 7500 lbs. or more (original 

TC or later increase). 

Require development of service instructions to correct 

designs that compromise ALI defined by TC holder 

under § 25.1815 within 24 months. Require within 24 

months after TC holder compliance with 25.1815 development of service instructions for a IMM or FRM 

for any tank with flammability above 7 percent, if located within the fuselage and normally emptied.

Applicants for future STCs or amendments to TCs that 

affect fuel tank system or IMM/FRM. 

25.1819 ................................ Requires IMM or FRM for any fuel tank on a passenger 

airplane with a flammability level that exceeds 7 percent. Fuel tanks located in the fuselage and normally 

emptied must meet § 25.981(b) level. Other fuel 

tanks must not exceed 7 percent.

Pending certification projects. 

Pre Amendment 102. 

Requires compliance with § 25.981(c) ............................ Post Amendment 102. 

25.1821 ................................ Requires any affected airplanes produced after a certain date to incorporate IMM or FRM.Manufacturers of certain airplane models. 

Appendix 25 K ..................... Establishes performance, reliability and reporting requirements for flammability reduction means.Applicants for approval of flammability reduction 

means. 

Appendix 25 L ...................... Defines flammability analysis method and input parameters that must be used in the analysis.Any person required to perform flammability analysis. 

91.1509, 121.917, 125.509, 

129.117.

Require retrofit of IMM or FRM into large airplanes with 

high flammability fuel tanks. Require large transport 

category airplanes manufactured after specific dates 

to have IMM or FRM in high flammability fuel tanks. 

Require incorporation of ALI into the maintenance 

program.

U.S. certificate holders and foreign persons operating 

U.S.-registered large transport category passenger 

airplanes. 

B. Ongoing Responsibility of Type 

Certificate Holders for Continued 

Airworthiness 

Several recent safety regulations 

necessitated action by air carriers and 

other operators but did not require 

design approval holders to develop and 

provide the necessary data and 

documents to facilitate the operators’

compliance. Operators are often 

dependent on action by a design 

approval holder before they can 

implement new safety rules. Ongoing 

difficulty reported by operators in 

attempting to meet these rules has 

convinced us that the corresponding 

design approval holder responsibilities 

may be warranted under certain 

70930 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

circumstances to enable operators to 

meet regulatory deadlines. 

We intend to require type-certificate 

holders, manufacturers and others to 

take actions necessary to support the 

continued airworthiness of and to 

improve the safety of transport-category 

airplanes. Such actions include 

performing assessments, developing 

design changes, revising instructions for 

continued airworthiness (ICA), and 

making available necessary 

documentation to affected persons. We 

believe this requirement is necessary to 

facilitate compliance by air carriers with 

operating rules that in effect demand the 

use of new safety features. 

To address this problem, we propose 

to amend subpart A of part 25 to expand 

its coverage and to add a new subpart 

I to establish requirements for current 

holders. As discussed in our final rule, 

‘‘Fuel Tank Safety Compliance 

Extension and Aging Airplane Program 

Update’’ (69 FR 45936, July 30, 2004), 

this and related proposals would add 

provisions to a new subpart I requiring 

actions by design approval holders that 

will allow operators to comply with our 

rules. 

Part 25 currently sets airworthiness 

standards for the issuance of TCs, and 

changes to those certificates, for 

transport category airplanes. It does not 

list the specific responsibilities of 

manufacturers to ensure continued 

airworthiness of these airplanes once 

the certificate is issued. Therefore, we 

propose to revise § 25.1 by adding 

paragraph (c) to make clear that part 25 

creates such responsibilities for holders 

of existing and supplemental type 

certificates for transport category 

airplanes, and applicants for approval of 

design changes to those certificates; we 

are also adding paragraph (d) to require 

design changes and other service 

activities by manufacturers when 

needed. In order to ensure the 

effectiveness of these changes, we 

would also amend § 25.2 (‘‘Special 

retroactive requirements’’) so as to 

require adherence to a new Subpart I 

which may require design changes and 

other activities by type certificate 

holders. 

This proposal would establish a new 

subpart I, Continued Airworthiness and 

Safety Improvements, where we would 

locate rules imposing ongoing 

responsibilities on design approval 

holders. In the past, this type of 

requirement took the form of a Special 

Federal Aviation Regulations (SFAR). 

SFARs are difficult to locate, because 

they are scattered throughout Title 14. 

Placing all these types of requirements 

in a single subpart of part 25, which 

contains the airworthiness standards for 

transport category airplanes, would 

provide ready access to critical rules. 

In preliminary discussions with 

foreign aviation authorities, with whom 

we try to harmonize our safety rules, 

they have expressed concern about 

consolidating parallel requirements in 

their counterparts to part 25. They have 

suggested that it may be more 

appropriate to place them in part 21 or 

elsewhere. Therefore, we specifically 

request comments from the public, 

including foreign authorities, on the 

appropriate place for these 

airworthiness requirements for type 

certificate holders. 

We reserve additional sections in this 

proposal to include other subparts we 

would expect to create with future aging 

airplane rules, several of which are 

under development. Some of these 

proposals include similar language 

establishing the general airworthiness 

responsibilities of manufacturers and 

thus include some overlapping 

provisions. Once any proposal 

establishing these broad responsibilities 

becomes a final rule, we will delete the 

duplicative requirements from the other 

proposals and retain only that language 

pertinent to any specific new safety 

regulations (such as fuel-tank 

flammability reduction). 

Except in one respect (discussed 

below), however, the ongoingairworthiness requirements in Subpart I 

would not by their terms reach 

applicants for TCs with respect to new 

projects for which application is made 

after the effective date of the proposed 

rule. This is unnecessary because, when 

we adopt a new requirement for TC 

holders, there will be a corresponding 

amendment to part 25 expressly making 

compliance with the new, or a similar 

safety standard a condition for receiving 

a TC in the future. For example, in this 

proposal, the new requirements of 

§ 25.981(b), (c) and (d) regarding FRM 

and IMM will govern future 

applications. 

For safety reasons, however, we are 

requiring that any application for a type 

design change, whenever filed, not 

degrade the level of safety already 

created by the TC holder’s presumed 

compliance with the subpart I rule. 

Currently, when reviewing an 

application for such a change, we 

employ the governing standards stated 

in part 21, specifically § 21.101. That 

section generally requires compliance 

with standards in effect on the date of 

application but contains exceptions that 

may allow applicants to show 

compliance with earlier standards. For 

example, if a change is not considered 

‘‘significant,’’ the applicant may be 

allowed to show compliance by 

pointing to standards that applied to the 

original TC. (See AC 21.101–1, 

‘‘Establishing the Certification Basis of 

Changed Aeronautical Products,’’ a copy 

of which can be downloaded from 

http://www.airweb.faa.gov/rgl). 

With the adoption of subpart I rules, 

we must ensure that safety 

improvements that result from TC 

holder compliance with these 

requirements are not undone by later 

modifications. Therefore, even when we 

determine under § 21.101 that an 

applicant need not comply with the 

latest airworthiness standards, it will be 

required to demonstrate that the change 

would not degrade the level of safety 

provided by the TC holder’s compliance 

with the subpart I rule. In the context of 

today’s proposal, for example, this will 

mean that an applicant for approval of 

a design change would have to show 

that it would not increase the fuel tank 

flammability above the limits defined in 

this proposal or adversely affect the 

FRM or IMM established by the TC 

holder. 

C. Applicability 

1. Manufacturers and Holders of Type 

Certificates, Supplemental Type 

Certificates and Field Approvals 

Today’s proposal, if adopted, will 

impose requirements on TC holders for 

all affected transport category airplanes 

as well as STC holders and operators 

who have field approvals for auxiliary 

fuel tank designs. Not all airplanes 

would require the installation of an 

FRM or IMM. Those requirements 

would be based on the initial average 

flammability exposure analysis 

discussed in detail later in this 

document. However, the TC, STC or 

field approval holder would be required 

to develop and provide limitations on 

the types of alterations and operations 

permitted for the airplane in order to 

retain the validity of that initial 

analysis. 

Today’s proposal, if adopted, would 

apply not only to domestic TC holders, 

but also to foreign TC holders. This rule 

would be different from most type 

certification programs for new TCs, 

where foreign applicants typically work 

with their responsible certification 

authority, and the FAA relies, to some 

degree, upon that authority’s findings of 

compliance under bilateral 

airworthiness agreements. No other 

certification authority has yet adopted 

requirements addressing fuel tank 

flammability for existing TCs. While 

some authorities have indicated an 

interest in adopting some type of 

requirements for new airplane designs, 

they may not adopt requirements 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70931 

applicable to existing TCs. Accordingly, 

the FAA will retain the authority to 

make all the necessary compliance 

determinations, and where appropriate 

may request certain compliance 

determinations by the appropriate 

foreign authorities using procedures 

developed under the bilateral 

agreements. The compliance planning 

provisions of this proposed rule are 

equally important for domestic and 

foreign TC holders and applicants, and 

we will work with the foreign 

authorities to ensure that their TC 

holders and applicants perform the 

planning necessary to comply with 

those requirements. 

As discussed briefly above, the 

proposed rule would require holders of 

existing type certificates to incorporate 

FRM or IMM into all new production 

airplanes if the fleet average 

flammability exposure level exceeds 

permissible levels. In past rulemakings 

where the FAA has required production 

cut-in of safety improvements, we have 

adopted rules prohibiting operators of 

airplanes produced after a specified date 

from operating those airplanes unless 

they are equipped with the 

improvements. This approach is 

effective in ensuring that U.S. operators 

receive the benefits of these safety 

improvements. But these rules do not 

apply to foreign operators, unless they 

operate U.S.-registered airplanes. 

By requiring FRM or IMM separately 

from the operational rules proposed in 

this notice, the proposed rule would 

improve the safety of the overall fleet of 

larger transport category airplanes. This 

requirement would also facilitate the 

secondary market for these airplanes. 

Even if a manufacturer initially sells an 

airplane to a foreign operator who may 

not be required to have the system, the 

operator may later sell or lease it to a 

U.S. operator. The U.S. operator would 

be able to simply place it into service, 

rather than having to install a system. 

Given the frequency of airplane 

transfers in today’s global economy, we 

think having these systems installed 

during production will provide 

significant long-term efficiencies since 

no retrofit would be required, as well as 

providing immediate safety benefits. 

2. Airplanes 

If adopted, this rule would apply, 

with some exceptions discussed below, 

to transport category turbine-powered 

airplanes with a maximum typecertificated capacity of 30 or more 

passengers, or a maximum payload 

capacity of 7500 pounds or more 

resulting from the original certification 

of the airplane or later increase in 

capacity. This would result in the 

coverage of airplanes where the safety 

benefits and the public interest are the 

greatest. 

We are proposing to apply this rule to 

airplanes for which a passenger capacity 

of 30 or more has been approved at any 

time. In the past, some designers and 

operators have obtained design change 

approval to slightly lower existing 

capacity to avoid applying requirements 

mandated only for airplanes over 

specified capacities. Today’s proposal 

would remove this possible means of 

avoiding compliance. It is also possible 

that an airplane design could be 

originally certificated with a capacity 

slightly lower than the minimum 

specified in this section, but through 

later design changes, the capacity could 

be increased above this minimum. 

Today’s proposal addresses both of 

these situations by proposing to regulate 

all airplanes that have been approved 

for carriage of 30 or more passengers, or 

7500-pound or more payload, at any 

time. 

We considered applying this proposal 

to all part 25 airplanes. This would have 

resulted in modifications to all fuel 

tanks located in the fuselage that are 

normally emptied. However, smaller 

airplanes generally do not have a 

significant number of high flammability 

exposure fuel tanks. Few of the smaller 

transport category airplanes in the 

current fleet have center wing tanks that 

are normally emptied. While some of 

the smaller airplanes have auxiliary or 

normally emptied fuel tanks located 

within the fuselage contour, many of 

these airplane types use differential fuel 

pressure to transfer the fuel from the 

fuel tanks. The increased pressure 

results in a reduction in the fuel tank 

flammability by keeping the fuel vapors 

at a level where ignition is unlikely. We 

have determined that the benefits of 

including these airplane types in this 

proposal are not sufficient to warrant 

the cost. 

Certain vintage airplanes type 

certificated before 1958, the beginning 

of the jet age, would be excluded from 

the requirements of this proposal. They 

are listed in § 25.1815(j). There are no 

known reciprocating-powered transport 

category airplanes currently in 

scheduled passenger service. 

Compliance would not be required for 

these specific older airplanes, because 

their advanced age and small numbers 

would likely make compliance 

economically impractical. If the public 

knows of other airplanes that may 

present unique compliance challenges, 

the FAA is interested in receiving 

comments. These comments may result 

in additional airplane models being 

excluded from the requirements of this 

proposed rule. 

The proposal does not extend to 

airplanes used in all-cargo operations. 

Our analysis of the costs of extending 

the proposal to include these airplanes 

does not appear to be justified by the 

associated benefits. The potential loss of 

life in a single accident is much smaller 

on all-cargo planes of the size 

contemplated by today’s proposal than 

on comparably sized passenger planes. 

The undiscounted cargo airplane costs 

would be about $261 million, with a 

present value of $110 million, while the 

benefits would be less than $1 million. 

However, the FAA does believe there is 

a risk to all-cargo airplanes because they 

share the same design features as at-risk 

passenger airplanes. We typically do not 

base our certification standards for 

transport category airplanes on use. 

Rather, our general philosophy is to 

address the performance characteristics 

of these airplanes because we believe all 

occupants should be protected against 

those designs that present a risk of 

serious injury or death. 

We have not evaluated the risk to allcargo airplanes because they are 

derivatives of passenger airplanes. The 

risk may be lower for all-cargo 

operations than for passenger 

operations. For example, if the risk of a 

fuel tank explosion per operating hour 

is the same for all-cargo planes as for 

passenger airplanes, the projected 

number of accidents for these planes is 

significantly less than one (0.15) in the 

next 50 years. This is because the 

projected number of miles flown by a 

cargo plane over the next 50 years is 

only 23 million miles. The risk may also 

be lower for all cargo operations because 

many cargo operations are conducted at 

night when the flammability of the fuel 

tanks is lower because of lower ambient 

temperatures. 

The 747 has both a passenger version 

and a freighter. The Monte Carlo 

analysis conducted for the 747 included 

both types of airplanes, and was 

weighted primarily toward the 

passenger airplane because they make 

up the majority of the 747 fleet. Thus, 

it should be possible to model the risk 

of a fuel tank explosion for cargo 

airplanes separate from passenger 

airplanes. We request flammability 

analyses on all-cargo airplanes and on 

the passenger versions of the same 

airplane model, as well as any 

underlying data. 

We have provided a breakdown of the 

estimated costs and benefits associated 

with requiring all-cargo airplanes be 

equipped with a means of reducing 

flammability in the preliminary 

regulatory evaluation. We believe that 

70932 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

the cost associated with providing a 

means of flammability reduction on 

newly designed cargo airplanes may be 

sufficiently low that it could make sense 

for all airplanes manufactured under a 

TC or amended TC applied for after the 

effective date of the final to have either 

an FRM or IMM. We believe there will 

be only a minimal cost associated with 

equipping newly designed all-cargo 

airplanes with a means of flammability 

reduction since the passenger version of 

the same model will be designed with 

such a system. 

We request comment on whether, 

given the costs involved, the design 

rules, the production cut-in rules, or the 

operating rules, if adopted, should be 

applied to all-cargo airplanes. 

Even with the categories of airplanes 

excluded that are discussed above, we 

recognize that this proposal is costly. To 

ensure that this rule is as cost effective 

as possible, we specifically request 

comments on whether there are other 

categories of airplanes or ways to 

distinguish among airplanes that would 

focus this rule on those where the 

benefits would be greatest. Any 

comments provided should include data 

to support the suggested exclusions or 

distinctions. 

3. Fuel Tanks 

The requirements proposed today 

would apply the proposed new FRM or 

IMM requirements to existing fuel tanks 

with a fleet average flammability 

exposure level that exceeds 7 percent. 

Main fuel tanks on existing airplanes, 

i.e., those that are designed both to feed 

fuel directly to one or more engines and 

to hold the required fuel reserves 

continually throughout each flight, are 

unlikely to be affected as they should 

have a fleet average flammability 

exposure level well below 7 percent. 

For any fuel tank that is normally 

emptied and has a fleet average 

flammability exposure level that 

exceeds 7 percent average flammability 

exposure, if any portion of the tank is 

located in the fuselage contour, the 

proposal would require TC STC and 

field approval holders to develop IMM 

or FRM that reduces the flammability 

exposure to 3 percent average 

flammability exposure and that meets 

the 3 percent warm day requirements. 

All other tanks with a fleet average 

flammability exposure level exceeding 7 

percent would need to incorporate IMM, 

or FRM. If FRM is installed it would 

need to provide a fleet average 

flammability exposure at one of two 

levels: Tanks on airplanes manufactured 

pursuant to a type certificate applied for 

prior to June 6, 2001 would have to have 

an exposure level no greater than 7 

percent; tanks on airplanes 

manufactured pursuant to a type 

certificate applied for after June 6, 2001 

would have to have an exposure level 

either no greater than 3 percent or 

equivalent to that of a comparable 

conventional unheated aluminum tank 

(which could be either more or less than 

3 percent). 

The ARAC found fuel tanks that are 

normally emptied have higher 

flammability exposure times than main 

tanks. Because these tanks contain a 

high percentage of ullage during a 

significant portion of most flights, a 

larger number of potential ignition 

sources are exposed to fuel vapor space 

for an extended time. Additionally, 

when they are within the fuselage 

contour, they are not naturally cooled 

by external air, which causes the fuel 

vapor to be flammable for a significant 

portion of the airplane operating time. 

Auxiliary fuel tanks are developed by 

TC holders, STC holders and, 

occasionally, by operators via field 

approvals, to increase the fuel capacity 

available on a type-certificated airplane. 

There are 74 different STCs for auxiliary 

fuel tanks in the airplanes potentially 

affected by the proposed rule. There are 

also field approvals for auxiliary tanks 

installed by airplane operators. Data 

submitted to the FAA as a result of 

SFAR 88 shows that fifteen of these 

auxiliary tanks have high flammability 

exposure fuel tanks. Some of these tanks 

have been installed in airplanes such as 

the DC–9 and DC–10 that do not have 

any other fuel tanks with high 

flammability exposure. Production of 

these airplane models ended long ago, 

so many of these airplanes will be at or 

near the end of their intended 

operational life at the end of the 

proposed compliance time given to the 

operators to incorporate FRM or IMM. 

Requiring the affected certificate holders 

to develop service instructions and the 

operators to incorporate FRM for these 

older fuel tanks increases the cost of the 

proposed rulemaking with fewer 

benefits than incorporation of FRM on 

newer airplane models. Therefore, the 

FAA specifically requests comments on 

including these auxiliary fuel tanks in 

the proposal. Information on the 

number of fuel tanks installed in the 

fleet and the remaining useful life of the 

affected airplanes should be provided. 

Portions of fuel tanks that are located 

within the fuselage contour include 

those in either the pressurized or 

unpressurized section of the fuselage or 

those whose surfaces make up part of 

the pressurized compartment. Fuel 

tanks located within the cargo 

compartment and center wing tanks are 

considered to be located in the fuselage 

contour. Many center tanks have 

portions that extend from the center 

wing box to the wing. The 

compartments of the tank located within 

the wing would also be considered part 

of the tank located within the fuselage 

contour and the same flammability 

requirements would apply. Fuel tanks 

located in the horizontal stabilizer, 

which also include segments located 

inside the fuselage and portions that 

extend outside the fuselage contour, 

would be assessed in the same way. 

Fuel tanks have also been located 

within the vertical stabilizer. If no 

portion of these tanks is in the fuselage, 

these tanks would not be considered as 

located within the fuselage boundary. 

4. Airplane Operators 

The rule proposed today would also 

apply to operators of the affected aircraft 

other than those who operate pursuant 

to 14 CFR part 135, Operating 

Requirements: Commuter and On 

Demand Operations and Rules 

Governing Persons On Board Such 

Aircraft. We are excluding part 135 

operators, because we have determined 

that only a few airplanes operated under 

part 135 would be subject to the rule. 

This is because part 135 is currently 

limited to a carrying of capacity of 10 

or fewer passengers and a payload of no 

more than 7,500 lb. We are in the 

process of revising part 135 and may 

consider increasing the payload 

capacity as part of that revision. If an 

increase in payload capacity is 

contemplated, we may also consider 

requiring FRM or IMM under part 135. 

As discussed previously, in an effort 

to enhance the cost effectiveness of this 

rule, we specifically request comments 

on whether other categories of 

operations should be excluded. Any 

comments provided should include data 

to support the suggested exclusions or 

distinctions. 

D. Proposed Requirements for 

Manufacturers and Holders of Type 

Certificates, Supplemental Type 

Certificates and Field Approvals 

1. New Airplane Designs 

Currently, § 25.981(c) establishes a 

requirement that fuel tank installation 

on all airplanes for which the type 

certificate was applied for after 2001 

must have either a ‘‘means to minimize 

the development of flammable vapors in 

the fuel tanks’’ that would ‘‘reduce the 

likelihood of flammable vapors, or a 

‘‘means to mitigate the effects of an 

ignition of fuel vapors * * *.’’ We 

propose amending this section to 

address new airplane designs. 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70933 

10These are cargo handlers and other persons 

who are typically carried on cargo-only airplanes to 

assist in the cargo operations. 

11 If this proposed amendment is not issued until 

after affected pending certification projects are 

completed, the final rule may revise the retrofit 

requirements proposed in § 25.1815 to reference 

Amendment 25–102 as the appropriate standard for 

fuel tanks on these airplanes other than those 

located in the fuselage. 

We propose to require those airplanes 

incorporating FRM to limit the fleet 

average flammability exposure to 3 

percent, and to limit warm day exposure 

to 3 percent, for all normally emptied 

fuel tanks located, in whole or in part, 

in the fuselage. All other fuel tanks 

could either meet the 3 percent average 

flammability exposure limitation or 

have a level that is no higher than the 

exposure level in a conventional 

unheated aluminum wing tank that is 

cooled by exposure to ambient 

temperatures during flight. The 

advantage of the first option is that 

manufacturers using unconventional 

designs would not be required to 

conduct the modeling on an equivalent 

unheated aluminum wing tank that is a 

purely theoretical design. The advantage 

of the second option is that a 

manufacturer could increase the level of 

acceptable exposure based on the 

exposure characteristics of this 

theoretical wing design. 

TC Applicants have proposed newer 

technology airplanes using composite 

wing skins or fuel tank designs with 

little exposed surface area. These 

designs may result in average fuel tank 

flammability exposure above the levels 

recommended by the ARAC. We expect 

future applicants will propose similar 

designs. For these airplane types, the 

applicant would have the option of 

demonstrating compliance by analyzing 

the fleet average flammability exposure 

of an equivalently designed wing made 

of aluminum for the model under 

evaluation. The thermal characteristics 

of the wing treated as a single fuel tank, 

as well as airplane specific parameters 

such as climb, cruise and descent 

profiles and flight length distribution, 

would be used as inputs to the 

flammability exposure analysis defined 

in Appendix L. This analysis would 

establish the maximum allowable 

flammability for the airplane model 

under evaluation. 

The safety objective of an ‘‘unheated 

aluminum wing tank’’ that is proposed 

as the standard in this notice is 

consistent with the ARAC 

recommendation and 14 CFR 25.981(c). 

It does not provide a numerical standard 

to apply in future type certification 

programs and the demonstration of 

compliance requires the applicant to 

conduct an analysis of their design to 

establish the flammability of a 

conventional unheated aluminum wing 

tank. In certain cases the compliance 

demonstration would be simplified if a 

numerical standard were provided in 

the regulation. Therefore we are 

proposing to establish a numerical 

flammability exposure standard of 3 

percent that can be used. This approach 

may have implementation advantages 

and should achieve the safety level 

intended by the ARAC recommendation 

and the current approach of § 25.981(c). 

We specifically request comments on 

which approach would be more 

workable and effective. If, based on 

comments received, we determine that a 

numerical standard alone is preferable, 

we may revise the final rule to adopt 

this approach. 

In addition to designing normally 

emptied fuel tanks that meet the 

proposed requirements, the TC holder 

would be required to provide 

airworthiness limitations designed to 

prevent exceeding the exposure limits of 

this rule or degrading the performance 

and reliability of FRM or IMM provided 

by the TC holder. For example, the 

manufacturer may state that any 

changes to the fuel system may 

invalidate its exposure analysis. In such 

an instance, the party making 

subsequent changes would need to 

conduct its own exposure analysis to 

ensure that the affected fuel tanks 

remain within the applicable limits. 

Likewise, a manufacturer may limit the 

type of jet fuel acceptable for its 

systems, as a jet fuel with a lower flash 

point may invalidate the initial 

exposure analysis. 

As discussed earlier, today’s proposal 

would not apply to airplanes designed 

solely for all-cargo operations. This 

exclusion applies to airplanes that, 

either as a result of initial type 

certification or through later design 

changes, have no passenger carrying 

capability, except for carriage of 

supernumeraries.10 Airplanes designed 

for all-cargo operations would continue 

to be subject to the existing 

requirements of § 25.981(c), which 

requires either means to minimize the 

development of flammable vapors in the 

fuel tanks or IMM. On the other hand, 

if an airplane that is designed for allcargo operations is converted to an 

airplane equipped to carry passengers, 

including a ‘‘combi’’ airplane (part 

cargo, part passenger), this design 

change would make the airplane subject 

to these proposed requirements. 

2. Existing Airplane Designs 

Holders of existing TCs would be 

required to first conduct a fleet average 

flammability exposure to determine 

whether the rule proposed today would 

apply to their fuel tanks. If the exposure 

level for normally emptied fuel tanks 

within the fuselage exceeds 7 percent, 

design changes and instructions for 

IMM or FRM that limit both overall and 

warm day fleet flammability exposure 

levels (discussed later) to no more than 

3 percent would need to be developed. 

All other normally emptied fuel tanks 

exceeding a 7 percent exposure limit 

would require design changes limiting 

exposure to 7 percent unless 

manufactured pursuant to a type 

certificate applied for after June 6, 2001, 

in which case the potentially more 

stringent requirements of existing 

§ 25.981(c) would continue to apply.11

Once design changes are developed, a 

second exposure analysis would need to 

be conducted to validate the design 

changes. 

Even if no changes to existing fuel 

tanks are required based on the fleet 

average exposure analysis, the 

manufacturer would be required to 

develop the same type of airworthiness 

limitations as those required for new 

airplane designs. 

The affected TC holders would also be 

required to submit compliance plans for 

the flammability analysis and the 

development of service instructions for 

an FRM or IMM. The contemplated 

compliance schedules and submissions 

are discussed later in this document. 

Finally, today’s proposal would 

require production cut-in for all 

airplanes manufactured after the 

required design changes are available. 

This section would apply only if the 

FAA has jurisdiction over the 

organization responsible for final 

assembly of the airplane. Section 

25.1821(a) uses the same terminology as 

Annex 8 to the Convention on 

International Civil Aviation, which 

defines the limits of the FAA’s authority 

under international law. In most cases, 

this refers to final assembly within the 

United States; there are limited 

circumstances where final assembly 

may occur in United States, but the 

responsible organization is under the 

jurisdiction of a foreign authority. It is 

also possible that final assembly could 

be done in another country by an 

organization over which the FAA has 

jurisdiction, such as a production 

certificate holder. 

3. Auxiliary Fuel Tanks 

Manufacturers and installers of 

auxiliary fuel tanks, whether 

manufactured under an amended TC, an 

STC or a field approval, would be 

required to conduct both an initial fleet 

70934 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

12With the adoption of rules requiring the retrofit 

of fuel tanks in certain airplanes, we have to 

consider different issues in deciding what standards 

applicants for design change approvals must meet. 

Otherwise, the safety improvements that result from 

TC holder compliance with these requirements 

could be undone by later modifications. Therefore, 

even if we determine under § 21.101 that it is not 

necessary to require these applicants to comply 

with the latest airworthiness standards, it is still 

necessary for them to show that the change would 

not degrade the level of safety provided by the TC 

holder’s compliance with the rule proposed today. 

13This methodology determines the fuel tank 

flammability exposure for numerous simulated 

airplane flights during which various parameters 

such as ambient temperature, flight length, fuel 

flash point are randomly selected. The results of 

these simulations are averaged together to 

determine the fleet average fuel tank flammability 

exposure. 

14As indicated in Appendix L, we intend to 

incorporate the users manual by reference into the 

final rule. 

15History of Monte Carlo method 

The method is called after the city in the Monaco 

principality, because of a roulette, a simple random 

number generator. The name and the systematic 

development of Monte Carlo methods dates from 

about 1944. 

The real use of Monte Carlo methods as a 

research tool stems from work on the atomic bomb 

during the second world war. This work involved 

a direct simulation of the probabilistic problems 

concerned with random neutron diffusion in fissile 

material; but even at an early stage of these 

investigations, von Neumann and Ulam refined this 

particular ‘‘ Russian roulette’’ and ‘‘splitting’’

methods. However, the systematic development of 

these ideas had to await the work of Harris and 

Herman Kahn in 1948. About 1948 Fermi, 

Metropolis, and Ulam obtained Monte Carlo 

estimates for the eigenvalues of Schrodinger 

equation. 

In about 1970, the newly developing theory of 

computational complexity began to provide a more 

average exposure analysis and an 

impact assessment. The first analysis 

would determine the exposure of the 

tanks for which they are responsible, 

while the second would determine 

whether those tanks negatively impact 

the flammability exposure of the tanks 

originally installed on the airplane. 

Changes to TCs, including installation 

of auxiliary fuel tanks or changes in the 

capacity of fuel tanks, may result in 

increased fuel tank flammability 

exposure or adversely affect FRM or 

IMM.12 Accordingly, the proposed rule 

would require a flammability exposure 

analysis of the auxiliary fuel tank 

design, an impact assessment to 

determine any adverse impact its design 

may have on the original or modified 

type design, and development of a 

flammability impact mitigation means 

(FIMM) to address adverse changes in 

flammability exposure. 

STC holders or applicants for an 

amended TC affected by the proposed 

rule would need to conduct a 

flammability analysis using the ‘‘Monte 

Carlo’’ method defined in proposed 

Appendix L and discussed later in this 

document. A number of inputs are 

required to conduct this analysis. 

Airplane specific data, such as fuel 

management, fuel tank thermal 

characteristics, or airplane climb rate 

may not be readily available from the 

original TC holder. We intend the STC 

holders to obtain the information by 

working with the TC holder and 

operators of airplanes that have their 

tanks installed. Applicants would need 

to work with prospective customers. 

Operators have business agreements 

with the original TC holders and in 

many cases access to TC holder 

information they obtained when they 

purchased the airplane. Conservative 

assumptions or business agreements 

with the original TC holders are other 

possible methods of gathering airplane 

type specific data needed for the 

analysis. 

If an increase in exposure above the 

allowable limits is identified, the holder 

of the STC or field approval would have 

to develop a FIMM and demonstrate 

how it will mitigate the impact of the 

increased exposure. One of the easiest 

methods may be simply deactivating the 

auxiliary tank or sealing off the venting 

to the affected tank. As another 

example, if an auxiliary fuel tank vents 

into a TC holder’s tank for which FRM 

is provided, the venting may have to be 

modified to prevent adversely affecting 

the FRM’s performance. 

Finally, a validation analysis would 

be required for the auxiliary tanks that 

demonstrates that the auxiliary tank 

flammability exposure levels, as 

modified with the addition of FRM or 

IMM, do not exceed the acceptable 

limits. Likewise, a validation analysis 

would be required to demonstrate that 

the FIMM is effective in maintaining the 

level of exposure in other tanks 

determined by the manufacturer of the 

other tank. As is the case for TC holders 

of existing airplanes, holders of STCs 

and field approvals would need to 

develop future airworthiness limitations 

and meet all mandated compliance 

schedules should they decide not to 

deactivate the fuel tank. 

For applicants for STCs and TC 

amendments, this proposal includes 

other design changes that could affect 

flammability exposure. Because this 

rule would require retrofit of airplanes 

to reduce flammability exposure, it 

would be counterproductive to allow 

future design changes that might negate 

the safety benefits of those retrofits. 

Any design change to a TC subject to 

the requirements proposed in today’s 

document that adds an auxiliary fuel 

tank, increases fuel tank capacity, or 

increases the flammability exposure of 

the existing fuel tank would have to 

meet the requirements of § 25.981 

proposed today. This requirement is 

intended to apply primarily to future 

design changes, but it may also apply to 

design change projects that are pending 

when this rule is issued. For example, 

in addition to applying for a new TC for 

the Airbus Model A380, Airbus has also 

applied for an amendment to that TC for 

the Model A380–800F (freighter 

derivative). Among other design 

changes, this TC amendment would 

incorporate a new fuel tank in the 

fuselage contour that is normally 

emptied. Under this proposal, this fuel 

tank would have to be shown to meet 

the requirements of proposed § 25.981. 

Because of the increased technical 

complexity of auxiliary fuel tank 

installations resulting from this 

proposal once this final rule is adopted, 

field approvals will no longer be granted 

for these tanks on airplanes affected by 

this rule. 

4. Methods of Mitigating the Likelihood 

of a Fuel Tank Explosion 

As noted above, TC and STC holders 

may need to make design changes to 

their fuel tanks located, in whole or in 

part, within the fuselage to decrease 

their level of flammability exposure. 

The rule proposed today offers two 

options, IMM or FRM. 

a. Flammability Analysis Using the 

Monte Carlo Method 

For all fuel tanks, an analysis must be 

performed to determine whether the 

fuel tank, as originally designed, meets 

the fleet average flammability exposure 

limits discussed above. By ‘‘average,’’

we mean that the analysis of each fuel 

tank must be averaged over the entire 

flammability exposure evaluation time 

(FEET) (see footnote 8) of each airplane 

in the entire fleet. To determine the 

flammability exposure of fuel tanks, the 

ARAC used a specific methodology 

referred to as the Monte Carlo method.13

We are proposing that any analysis of a 

fuel tank must be performed in 

accordance with this methodology, as 

detailed in proposed Appendix L and in 

the FAA document, Fuel Tank 

Flammability Assessment Method Users 

Manual.14 We considered approving 

alternative methodologies in lieu of 

Appendix L, but we found that no other 

alternative considered all factors that 

influence fuel tank flammability 

exposure, which is the safety objective 

of this proposal. 

The Monte Carlo method,15 as 

commonly understood by scientists, is 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70935 

precise and persuasive rationale for employing the 

Monte Carlo method. The theory identified a class 

of problems for which the time to evaluate the exact 

solution to a problem within the class grows at least 

exponentially with M. The question to be resolved 

was whether or not the Monte Carlo method could 

estimate the solution to a problem in this 

intractable class to within a specified statistical 

accuracy in time bounded above by a polynomial 

in M. Numerous examples now support this 

contention. Karp (1985) shows this property for 

estimating reliability in a planar multiterminal 

network with randomly failing edges. Dyer (1989) 

establish it for estimating the volume of a convex 

body in M-dimensional Euclidean space. Broder 

(1986) and Jerrum and Sinclair (1988) establish the 

property for estimating the permanent of a matrix 

or, equivalently, the number of perfect matchings in 

a bipartite graph. Discussion derived from History 

of the Monte Carlo Method, Sabri Pllana, http:// 

geocities.com/College Park/Quad/2435/index.html. 

useful for obtaining numerical solutions 

to problems which are too complicated 

to solve analytically. The method 

provides approximate solutions to a 

variety of mathematical problems by 

performing statistical sampling 

experiments on a computer. The method 

applies to problems with no 

probabilistic content as well as to those 

with inherent probabilistic structure. 

Our use of this method to analyze fuel 

tank flammability exposure and define 

acceptable limits is based on the 

recommendation of the ARAC, which 

compared the flammability exposure of 

conventional unheated aluminum wing 

fuel tanks to that of tanks that are 

located within the fuselage contour and 

heated by adjacent equipment. Use of 

the Monte Carlo method allows us to 

consider variables from within defined 

distributions that represent possible 

operating conditions for the flight. The 

results of a large number of flights can 

then be used to approximate average 

flammability exposure over a large fleet 

of airplanes. 

Variables include those affecting all 

airplanes in the transport category 

airplane fleet, such as: (1) Ground, 

overnight, and cruise air temperatures 

likely to be experienced worldwide; (2) 

fuel properties; and (3) conditions when 

the tank in question will be considered 

flammable. In addition, the analysis 

factors in specific airplane models 

characteristics, such as climb and 

descent profiles, fuel management, heat 

transfer characteristics of fuel tanks, 

maximum airplane operating 

temperature limitations, maximum 

airplane range for the airplane model, 

and the effectiveness of FRM (if 

installed). 

The flammability analysis must 

include any model variations and 

derivatives for which the TC holder has 

obtained approval that affect fuel tank 

flammability exposure. Model variations 

that may affect fuel tank flammability 

could include changes in the fuel tank 

volume or usable fuel capacity, changes 

in the fuel management procedures, and 

engine changes that might affect 

parameters such as airplane climb rate 

or bleed air available if needed by an 

FRM. Other examples of configuration 

differences that may affect fuel tank 

flammability exposure are provided in 

the discussion of § 25.1817. The 

flammability analysis would also 

include all modifications and changes 

mandated by ADs that affect fuel tank 

flammability exposure as of the effective 

date of the rule. These ADs would only 

be those issued against any 

configurations developed by TC holders. 

The analysis would not address any 

ADs issued against modifications 

defined by a third party STC installed 

on affected airplanes. The result would 

be a configuration that is clearly 

understood by both industry and the 

FAA. 

Mass loading and changes in fuel 

vapor concentration caused by fuel 

condensation and vaporization have 

been excluded from the flammability 

exposure analysis. The method used by 

the ARAC to establish the flammability 

exposure value as the benchmark for 

fuel tank safety for wing fuel tanks did 

not include the effects of cooling of the 

wing tank surfaces and the associated 

condensation of vapors from the tank 

ullage. If this effect had been included 

in the wing tank flammability exposure 

calculation, it would have resulted in a 

significantly lower wing tank 

flammability exposure benchmark 

value. The ARAC analysis also did not 

consider the effects of the low fuel 

condition (or ‘‘mass loading’’) which 

would lower the calculated 

flammability exposure value for fuel 

tanks that are routinely emptied, such as 

center wing tanks. When the amount of 

fuel is reduced to very low quantities 

within a fuel tank, there may be 

insufficient fuel in the tank to allow 

vaporization of fuel to the concentration 

that would be predicted for any 

particular temperature and pressure. 

The effect of condensation and 

vaporization in reducing the 

flammability exposure of wing tanks is 

comparable to the effect of the low fuel 

condition in reducing the flammability 

exposure of center tanks. Therefore, we 

consider these effects to be offsetting, so 

that by eliminating their consideration, 

the analysis will produce results for 

both types of tanks that are comparable. 

Accordingly, both factors have been 

excluded when establishing the 

flammability exposure limits in this 

proposal. During development of the 

harmonized special conditions for the 

Boeing 747, the FAA and the European 

Joint Aviation Authorities (JAA)/EASA 

agreed that using the ARAC 

methodology provides a suitable basis 

for determining the flammability of a 

fuel tank and consideration of these 

effects should not be permitted. 

Using these variables, the Monte Carlo 

method would then be applied to a 

statistically significant number of flights 

(1,000,000), where each of the factors 

described above is randomly selected. 

The flights selected are representative of 

the fleet using the defined distributions 

of the variables. For example, flight one 

may be a short flight on a cold day with 

an average flash point fuel. Flight two 

may be a long flight on an average day 

with a low flash point fuel. This process 

is repeated until 1,000,000 flights have 

been defined in this manner. 

For every one of the 1,000,000 flights, 

the Monte Carlo program calculates the 

amount of time the bulk average fuel 

temperature and ambient pressure in the 

fuel tank or compartment of interest 

would result in the fuel vapor being 

within the flammable range. This 

calculation is then used, in combination 

with the oxygen concentration in the 

fuel tank (if an FRM is installed), to 

establish whether the fuel tank is 

flammable. Averaging the results for all 

1,000,000 flights provides an average 

flammability exposure for the fleet of 

airplanes of a particular model type. 

The determination of whether the fuel 

tank ullage is flammable is based on the 

temperature of the fuel in the tank or the 

compartment of interest, determined by 

the tank thermal model, the atmospheric 

pressure in the fuel tank, and properties 

of the fuel loaded for a given flight, 

which is randomly selected from data 

provided in tables in this appendix. 

The Monte Carlo methodology has 

previously been recommended by 

ARAC and has been used in previous 

analyses by the affected certificate 

holders in evaluating the flammability 

exposure of fuel tanks conducted as part 

of evaluating the findings of SFAR 88. 

Therefore we expect the affected type 

certificate holders already have a good 

understanding and can comply with this 

requirement within the proposed 

timeframe of 150 days. 

b. Ignition Mitigation Means 

The proposed rule maintains the 

option introduced by Amendment 25–

102 for affected manufacturers to use 

ignition mitigation as a means of 

protecting the airplane from the hazards 

associated with fuel tank flammability. 

IMM is a passive system that requires 

little attention once installed. IMM does 

not prevent an ignition in the fuel tank; 

rather, material absorbs the heat created 

by the fire. While a small fire could 

occur, an IMM system eliminates the 

70936 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

possibility of a catastrophic fuel tank 

explosion. 

We acknowledge that IMM presents 

maintenance challenges. The mitigation 

means (such as polyurethane foam, 

metal foil products and explosion 

suppression systems discussed within 

AC 25.981–2) must be reinstalled 

exactly as removed when the fuel tanks 

are opened up for maintenance actions. 

Replacement is particularly difficult 

because all voids must be removed. It 

also appears that the materials used for 

mitigation (particularly the 

polyurethane foams) may be prone to 

compression, thus reducing the usable 

life of the material. 

Nevertheless, given the potential 

effectiveness of IMM, the FAA believes 

we should continue to allow installation 

of IMM as a means of compliance with 

the requirements proposed today. A 

detailed discussion of acceptable means 

of compliance for manufacturers 

choosing to comply with the IMM 

option is provided in AC–25.981–2. 

c. Flammability Reduction Means 

Alternatively, a TC or STC holder 

could decide to use an FRM that limits 

the exposure level of the tanks. For fuel 

tanks that are normally emptied and 

located within the fuselage contour, the 

exposure would have to be limited to 3 

percent under two sets of conditions, 

overall fleet exposure and warm day 

fleet exposure. Both of these conditions 

would be evaluated using the Monte 

Carlo method described below. For all 

other fuel tanks, the 3 percent limit 

would apply only to the overall fleet 

exposure. 

The proposed flammability exposure 

requirements are intended to provide an 

additional layer of protection to the 

existing certification standards that 

require designs to preclude fuel tank 

ignition sources. This balanced risk 

management approach of precluding 

ignition sources and reducing 

flammability exposure in certain fuel 

tanks provides two independent layers 

for preventing fuel tank explosions in 

those tanks. The proposed requirements 

could be met by a highly reliable 

‘‘single-string’’ (non-redundant) 

inerting-based FRM, allowing for 

limited operation of airplanes with an 

inoperative FRM until repairs could be 

made. These requirements could also be 

met by a cooling-based FRM. 

Compliance with these requirements 

has been shown to be practical using 

existing technology. 

i. Accounting for System Reliability and 

Performance Issues 

As discussed in the background 

section of this document, previous 

studies of inerting-based FRM showed 

that, if inerting systems were required to 

be operational for all flights, the system 

would be required to have at least some 

redundant design features and would 

not be practical. That is, it would 

require most components to be 

duplicated to provide a back-up 

function in the event the primary 

component failed. A requirement for a 

redundant FRM that would continue to 

operate after component failure would 

increase the weight and complexity of 

an inerting system. This may result in 

a system that would not be practical for 

commercial airplanes at this time. The 

overall fleet flammability exposure 

analysis would assume some periods of 

inoperability. However, we would 

require that the contribution to average 

flammability exposure due to either 

reliability (during periods when the 

system is inoperative) or system 

performance (during periods when the 

system does not have the capacity to 

maintain a non flammable tank), be 

limited to 1.8 percent. This gives the 

designer freedom to engineer the 

system, and allows for some operation 

of airplanes with an inoperative FRM 

until repairs can be made at an 

appropriate maintenance facility. 

ii. Warm Day Fleet Flammability 

Exposure 

The warm day exposure analysis is 

intended to ensure minimum FRM 

system performance levels when there is 

the greatest risk to safe flight. Therefore, 

the 3 percent flammability exposure 

limit excludes system reliability related 

contributions that are included in the 

overall fleet flammability exposure 

assessment. Compliance with this 

proposal would require conducting an 

analysis in accordance with Appendix L 

for each of the specific phases of flight 

during warmer day conditions defined 

in the proposal. The flammability 

exposure of the tank in question would 

be determined for the ground, takeoff 

and climb phases as separate values, 

without including the times when the 

FRM is not available because of failures 

of the system or dispatch with the FRM 

inoperative. The fleet flammability 

exposure level of each fuel tank for 

ground, takeoff, and climb phases of 

flight during warm days must not 

exceed 3 percent of the flammability 

exposure evaluation time in each of the 

three phases. 

iii. Reliability Reporting 

Today’s proposal, if adopted, would 

require that the applicant demonstrate 

effective means to ensure collection of 

FRM reliability data so that the effects 

of component failures can be assessed 

on an on-going basis. The proposed 

reporting requirement applies to 

applicants and holders of the affected 

TCs, STCs, and field approvals. 

The rule would require the TC or STC 

holder to provide the FAA with 

summaries of the FRM reliability data 

and compliance with Appendix K on a 

quarterly basis for the first five years 

after the FRM is installed and 

operational. After that time, continued 

quarterly reporting requirements may be 

replaced with other reliability tracking 

methods approved by the FAA oversight 

office. The requirement for quarterly 

reports may be eliminated if the FAA 

determines that the reliability of the 

FRM meets, and will continue to meet, 

the requirements of the rule. 

Operators would not be required to 

report FRM reliability information. We 

intend TC holders to gather the needed 

data from operators using existing 

reporting systems that are currently 

used for airplane maintenance, 

reliability and warranty claims. We 

anticipate the operators would provide 

this information through existing 

business arrangements between the TC 

holders and the airlines. 

iv. Reliability Indication and 

Maintenance Access 

The proposed rule would require that 

indicators be provided to identify 

failures of the FRM, so that appropriate 

actions can be taken to maintain the 

reliability of the FRM. The need to 

provide indication of the FRM status 

will depend on the particular FRM 

design. Various design methods may be 

used to make sure an FRM meets the 

reliability and performance 

requirements. These may include a 

combination of system integrity 

monitoring and indication, redundancy 

of components, and maintenance 

actions. A combination of maintenance 

indication or maintenance check 

procedures could be used to limit 

exposure to latent failures within the 

system, or high inherent reliability may 

be used to make sure the system will 

meet the fuel tank flammability 

exposure requirements. 

The need for FRM indications and the 

frequency of checking system 

performance (maintenance intervals) 

must be determined as part of the FRM 

fuel tank flammability exposure 

analysis. The determination of a proper 

maintenance interval and procedure 

will follow completion of the 

certification testing and demonstration 

of the system’s reliability and 

performance prior to certification or as 

part of the FAA review process for 

airplanes manufactured under existing 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70937 

TCs or auxiliary fuel tanks under 

existing STCs. 

The rule would also require that 

sufficient accessibility to FRM status 

indications be provided for maintenance 

personnel. We intend that maintenance 

personnel or the flightcrew have access 

to any indications that must be accessed 

at intervals established by the FRM 

design approval holder when 

demonstrating compliance with the 

reliability requirements for the FRM. 

Access doors and panels to the fuel 

tanks with FRMs and to any other 

enclosed areas that could contain 

hazardous atmosphere under either 

normal conditions or failure conditions 

would need to be permanently 

stenciled, marked, or placarded to warn 

maintenance personnel of the possible 

presence of a potentially hazardous 

atmosphere. The proposal for markings 

does not alter the existing requirements 

that must be addressed when entering 

airplane fuel tanks. 

d. Service Instructions and Service 

Bulletins 

If the flammability exposure analysis 

shows that the average exposure level 

for any fuel tank exceeds 7 percent, the 

TC holder would be required to develop 

design changes and service instructions 

for either FRM or IMM. 

Modifications incorporated into 

existing airplanes, including safety 

related changes (design and/or 

maintenance) that are mandated by AD, 

are typically made by operators using 

service instructions developed by the 

TC holders, commonly referred to as 

service bulletins. In this proposal, 

service instructions must contain 

sufficient information for the operator to 

incorporate the design change and any 

associated procedures and airworthiness 

limitations. They may include specific 

step-by-step procedures and information 

needed by the operator, such as parts 

lists and drawings. Therefore, the 

proposed rule would require TC holders 

to develop and submit for approval by 

the FAA, not just data defining a 

proposed design change, but all of the 

information necessary to enable an 

operator to comply with the proposed 

operational rules, discussed later. 

e. Critical Design Configuration Control 

Limitations (CDCCL) 

If adopted, the rule would require 

defining airworthiness limitations, 

including Critical Design Configuration 

Control Limitations (CDCCL), 

inspections, and other procedures for 

fuel tanks to prevent exceeding the 

applicable flammability exposure limits. 

For this proposal, CDCCL include those 

features of the design that must be 

present or maintained for compliance 

with the requirements of § 25.981(b) and 

(c) for the operational life of the 

airplane. For example, certain fuel tanks 

may rely on natural cooling to meet the 

flammability exposure levels within this 

proposal. Changes to the airplane, such 

as installing a fuel re-circulation system, 

hydraulic heat exchanger in the fuel 

tank, or a heat source adjacent to the 

fuel tank, may affect fuel tank 

flammability. The CDCCL would be 

necessary in this example to prohibit 

the addition of heat to the fuel tank. 

Another example of CDCCL might 

include limits on operation with certain 

fuel types such as JP–4. We expect all 

fuel tanks, even those in airplanes that 

do not have high flammability fuel 

tanks, would need to have CDCCL 

defined so that future modifications do 

not increase the flammability above the 

mandatory limit. The proposal applies 

the same requirements already applied 

to fuel tank ignition source prevention 

in § 25.981(b) to the FRM or IMM. 

The proposal also includes the 

requirement that visible means 

identifying CDCCL are present. Our 

intent here is to prevent alterations to 

critical features of the system. As the 

visible identifications are critical to the 

FRM or IMM system, they are also 

considered to be CDCCL. Any tampering 

or removal would be in violation of the 

CDCCL. These CDCCL, inspections, or 

other procedures would be documented 

as airworthiness limitations in the ICA. 

Under the proposal, all fuel tanks, 

regardless of flammability exposure, 

must be subject to airworthiness 

limitations consisting of CDCCL, 

inspections, or other procedures. The 

purpose of these limitations is to 

prevent increasing the flammability 

exposure of the tanks above that 

permitted under this section and to 

prevent degradation of the performance 

of any means installed in accordance 

with this section. For example, certain 

fuel tanks may rely on natural cooling 

or use of certain fuel types to meet the 

flammability levels within this 

proposal. Therefore, CDCCL may be 

required that define the critical features, 

such as—

• Flammability exposure of the 

unheated aluminum wing tank, 

• Cooling rate, 

• Limits on heat input, 

• Limits on use of high volatility fuels 

such as JP–4, 

• Quantity of engine bleed air flow 

that is used for inerting, 

• Limits on penetrations of the fuel 

tank, 

• Limits on any changes to fuel 

management that may affect FRM, 

• Limits on changes to any placards 

or means used to visibly identify critical 

design features of the fuel tank system 

that must not be compromised for the 

operational life of the airplane. 

As discussed above, airworthiness 

limitations, such as those proposed 

today, are part of the ICA. TC holders 

would need to make available to 

affected parties pertinent changes to the 

ICAs. (The term ‘‘make available’’ is 

used in the same sense that it is used 

in § 21.50.) We do not intend by this 

proposal to alter or interfere with the 

existing commercial relationships 

between TC holders and these other 

persons. We anticipate that TC holders 

would be able to be reasonably 

compensated for developing these 

documents, as they are under current 

practice. 

The proposed rule would require 

creation of an Airworthiness Limitations 

Section (ALS), unless previously 

established. The ALS is required by 

current part 25 and includes those items 

that have mandatory inspection or 

replacement times related to fuel 

systems and structure. The ALS is 

included in the ICA, approved as part of 

certification, and distributed with an 

airplane on delivery. In this way the 

ALS is visible to all who need it and 

who would be required to comply with 

it under §§ 91.1509, 121.917, 125.509 

and 129.117 of this proposal. The 

current part 25 ALS and ICA 

requirements apply only to airplane 

types for which the TC application was 

made after Amendment 25–54 (adopted 

in 1981) and were developed for 

structural considerations. As a result, 

they are not applicable to many current 

airplanes and do not currently contain 

information for other systems. 

For those TC holders of airplanes that 

currently do not have an ALS, the intent 

of this proposal is to require an ALS 

only for fuel tank safety related limits. 

This proposal would not require that the 

ALS for these airplanes include the 

other requirements for an ALS 

established under Amendment 25–54 to 

part 25, or a later amendment. For those 

TC holders or applicants with airplanes 

certified to Amendment 25–54 or later, 

the existing ALS would be revised to 

include the fuel tank system 

airworthiness limitation items (ALI). 

f. Compliance Planning 

Historically, the FAA has worked 

together with the TC holders when 

safety issues arise, in order to identify 

solutions and actions that need to be 

taken. Some of the safety issues that 

have been addressed by this process 

include those involving aging aircraft 

structure, thrust reversers, cargo doors, 

70938 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

and wing icing protection. While some 

manufacturers have promptly addressed 

these safety issues and developed 

service instructions, others have not 

applied the resources necessary to 

develop service instructions in a timely 

manner. This has caused delay in the 

adoption of corrective action(s). A more 

uniform and expeditious response is 

necessary to address fuel tank safety 

issues. Because this proposal sets a 

precedent in introducing part 25 

requirements for holders of existing 

TCs, changes to existing TCs, and 

manufacturers, it is the FAA’s 

expectation that they will work closely 

with the FAA oversight office in putting 

together a compliance plan for 

developing the required FRM or IMM. 

In order to provide TC holders and 

the FAA with assurance that the TC 

holders understand what means of 

compliance is acceptable and have 

taken necessary actions (including 

assigning sufficient resources) to 

achieve compliance with the proposed 

rule, we are proposing a compliance 

planning requirement. This requirement 

is based substantially on ‘‘The FAA and 

Industry Guide to Product 

Certification,’’ which describes a 

process for developing project-specific 

certification plans for type certification 

programs. This Guide may be found in 

the docket. This planning requirement 

would not apply to future applicants for 

TCs. Since this type of planning 

routinely occurs at the beginning of the 

certification process, no additional 

compliance planning is required for 

future applicants. 

The Guide recognizes the importance 

of ongoing communication and 

cooperation between applicants and the 

FAA. The proposed planning schedule, 

while regulatory in nature, is intended 

to encourage establishment of the same 

type of relationship in the process of 

complying with this rule, if adopted. 

One of the items required in the plan 

is, ‘‘If the proposed means of 

compliance differs from that described 

in FAA advisory material, a detailed 

explanation of how the proposed means 

will comply with this section.’’ FAA 

advisory material is never mandatory, 

because it describes one means, but not 

the only means of compliance. In the 

area of type certification, applicants 

frequently propose acceptable 

alternatives to the means described in 

advisory circulars. But when an 

applicant chooses to comply by an 

alternative means, it is important to 

identify this as early as possible in the 

certification process to provide an 

opportunity to resolve any issues that 

may arise that could lead to delays in 

the certification schedule. 

The same is true for the fuel tank 

flammability reduction requirement. As 

discussed earlier, timely compliance 

with this section is necessary to enable 

operators to comply with the 

operational requirements of this 

proposal. Therefore, this item in the 

plan would enable the FAA oversight 

office to identify and resolve any issues 

that may arise with the compliance plan 

without jeopardizing the TC holders 

ability to comply with this section by 

the compliance time. 

i. Compliance Plan for Flammability 

Exposure Analysis 

The proposed rule would require 

submission of a compliance plan within 

60 days of the effective date of the final 

rule for the flammability exposure 

analysis required by the proposed rule. 

The intent of the proposal is to promote 

early planning and communication 

between the certificate holders and the 

FAA. The exposure analysis would need 

to be completed within 150 days of the 

rule’s effective date. Thus, the 60 day 

planning submission should provide 

sufficient time for the FAA to discuss 

any concerns that it may have over how 

the affected party intends to analyze 

fleet average flammability exposure. 

ii. Compliance Plan for Design Changes 

and Service Instructions 

Under today’s proposal, each holder 

of an existing TC would need to submit 

to the FAA oversight office a 

compliance plan for developing design 

changes and service instructions within 

210 days of the rule’s effective date. 

TC holders and applicants would 

have to correct a deficient plan, or 

deficiencies in implementing those 

plans, in a manner identified by the 

FAA oversight office. Deficiencies in the 

compliance plan would need to be 

corrected within 30 days of notification 

by the FAA. This approach differs from 

the original type approval process. 

Applicants for type certificates face 

commercial pressures, not regulatory 

deadlines, so the FAA can permit them 

to resolve identified deficiencies on 

their own schedule. Such leeway is not 

appropriate here because operators who 

are subject to regulatory deadlines are 

dependent on TC holders’ timely 

compliance with these requirements. 

However, before the FAA formally 

notifies a TC holder or applicant of 

deficiencies, we will contact it to try to 

understand the deficiencies and develop 

a means of correcting them. Therefore, 

the notification referred to in this 

paragraph should document the agreed 

corrections. 

The ability of an operator to comply 

with the proposed operating rules will 

be dependent on TC holders complying 

with the requirement to develop design 

changes and service instructions. The 

FAA intends to carefully monitor 

compliance and take appropriate action 

if necessary. Failure to comply by the 

dates specified in the final rule would 

constitute a violation of the 

requirements and could subject the 

violator to certificate action to amend, 

suspend, or revoke the affected 

certificate (49 U.S.C. 44709). It could 

also subject the violator to a civil 

penalty of not more than $25,000 per 

day per certificate until § 25.1815 is 

complied with (49 U.S.C. 46301). 

iii. Compliance Plan for Auxiliary Fuel 

Tanks 

The proposed rule would also 

establish a timeframe in which affected 

STC holders, applicants for an amended 

TC, and operators using fuel tanks 

pursuant to a field approval must 

submit for approval (to the FAA 

oversight office) a flammability 

exposure analysis for their design 

changes. The proposal includes a 12- 

month timeframe to complete the 

analysis. Any applicant whose STC or 

TC amendment is not approved within 

the 12-month compliance period would 

have to complete the analysis before 

approval. 

The proposed rule would also require 

submission for approval of an impact 

assessment of the fuel tank system, as 

modified by the STC holder’s design 

change. The purpose of this proposal is 

to identify any features of the 

modification to the original type design 

that may violate the critical design 

configuration control limitations 

developed by the original TC holder. 

For example, if an FRM that utilized 

inerting is incorporated into an airplane, 

a CDCCL would likely be developed that 

would limit venting of air into the fuel 

tank, because it could introduce oxygen 

into the tank, resulting in a flammable 

vapor space. In this case the STC holder 

would need to assess its design and 

identify any violation of the CDCCL 

identified for the FRM. Results from the 

analysis would be provided to the FAA 

in the form of a report or summary 

letter. 

Supplemental type certificate holders 

would have to submit the impact 

assessment within six months after we 

approve the TC holder’s CDCCL. 

Applicants whose design changes are 

not approved within that six-month 

period would have to submit the 

assessment before approval of the 

change. Once the CDCCL is approved, 

the TC holder would be required to 

make them available to other affected 

persons, including those subject to this 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70939 

16 Flight-Testing of the FAA Onboard Inert Gas 

Generation System on an Airbus A320, DOT/FAA/ 

AR–03/58, dated June 2004. 

section. We consider the six-month 

period more than enough to perform the 

required assessment. The resulting 

service instructions would be required 

to show compliance with the applicable 

flammability requirements and to 

address any adverse effects of the design 

change on any IMM or FRM developed 

by the TC holder. 

g. Compliance Schedule 

Table 2 contains compliance dates for 

the required submissions. This table 

provides specific dates for each Boeing 

and Airbus model airplane that has fuel 

tanks whose average flammability 

exposure exceeds 7 percent. A 

compliance time of 24 months from the 

effective date of the final rule is 

proposed for all other models subject to 

this proposal (if the flammability 

exposure analysis shows an average 

exposure level exceeding 7 percent). We 

established the compliance dates 

proposed in this table after 

consideration of the time needed by the 

TC holders to develop the means to 

address fuel tank flammability 

exposure. We anticipate development of 

an FRM or IMM would take the affected 

TC holder about 2 years. The dates in 

the proposal were based on the 

assumption that it would be adopted 

well before the end of 2005. However, 

the rulemaking process took longer than 

originally anticipated. Consequently, 

given the specific compliance dates I the 

proposed rulemaking and the likelihood 

that finalization of the rules will be later 

than expected, there may not be as 

much time allowed for compliance as 

originally planned. We recognize that 

compliance intervals may need to be 

adjusted and will consider your 

comments on this condition. 

On February 17, 2004, the FAA 

Administrator announced that the 

agency is developing a proposal for new 

rules that would require reducing the 

flammability exposure of new 

production transport category airplanes 

and existing transport category airplanes 

with high-flammability fuel tanks. Since 

then, Boeing has announced plans to 

incorporate FRM in newly produced 

airplanes and to make service 

instructions available for the airplane 

models listed in this notice. Boeing has 

also submitted applications for type 

certification of flammability reduction 

systems. On February 15, 2005, we 

published a Special Conditions No. 25–

285–SC for flammability reduction 

means on the Boeing Model 747 (70 FR 

780068563). Airbus flew an A320 16 in 

August 2003 with the prototype FAA 

inerting system, but has not committed 

to production incorporation or 

development of service instructions for 

any flammability reduction means on its 

airplane models. 

While Airbus and Boeing may have 

less than 2 years from the effective date 

of the final rule to develop an FRM or 

IMM for some of their models, we know 

that both companies have been 

considering these improvements well in 

advance of this rulemaking. The 

proposed compliance dates are thus 

staggered to allow the engineering 

resources of the TC holders to develop 

design means for all of their models. 

The proposed dates are established 

based on both our assessment of when 

it is feasible for TC holders to comply 

and the risks associated with particular 

airplane models, due to the 

flammability of the fuel tanks and 

numbers of airplanes in the fleet. For 

example, the Boeing Model 747 is first, 

followed by the Boeing Model 737. The 

first Airbus model affected is the A320. 

The proposed dates will support the 

retrofit of airplanes at the earliest 

reasonable time to achieve the safety 

benefits intended by this rulemaking. 

The compliance times proposed for 

airplane and fuel tank manufacturers are 

also used as the basis for the proposed 

compliance dates for introduction of 

these systems into the operators’ fleets 

under parts 91, 121, 125, and 129. 

Extension of the compliance dates for 

development of the service instructions 

by the certificate holders would either 

reduce the amount of time available to 

operators or delay full deployment of 

these safety improvements. As 

discussed later in this proposal for the 

operational requirements, incorporation 

of FRM or IMM will likely require 

access inside the fuel tanks. 

TABLE 2 

Model Service instruction 

submittal date 

Boeing 

747 Series ............... December 31, 2005. 

737 Series ............... March 31, 2006. 

777 Series ............... March 31, 2006. 

767 Series ............... September 30, 2006. 

757 Series ............... March 31, 2007. 

707/720 Series ........ December 31, 2007. 

Airbus 

A319, A320, A321 

Series.

December 31, 2006. 

A300, A321 Series .. June 30, 2007. 

A330, A340 Series .. December 31, 2007. 

All other affected 

models.

Within 24 months of 

effective date of this 

amendment. 

E. Proposed Requirements for Airplane 

Operators 

The proposed operating rules would 

prohibit the operation of certain 

transport category airplanes operated 

under parts 91, 121, 125, and 129 

beyond specified compliance dates, 

unless the operator of those airplanes 

has incorporated approved IMM, FRM 

or FIMM modifications and associated 

airworthiness limitations for the 

affected fuel tanks. The proposed rules 

would not apply to airplanes used only 

in all-cargo operations. 

This rulemaking also includes a 

proposal to create new subparts that 

pertain to the support of continued 

airworthiness and safety improvements 

in the following parts of Title 14 Code 

of Federal Regulations: 

• Part 91, General Operating and 

Flight Rules; 

• Part 121, Operating Requirements: 

Domestic Flag and Supplemental 

Operation; 

• Part 125, Certification and 

Operation: Airplanes Having a Seating 

Capacity of 20 or More Passengers or a 

Maximum Payload Capacity of 6,000 

Pounds or More; and Rules Governing 

Persons On Board Such Aircraft; and 

• Part 129, Operations: Foreign Air 

Carriers and Foreign Operators of U.S.- 

registered Aircraft Engaged in Common 

Carriage. 

As discussed earlier, this proposal 

does not include part 135, since the 

number of airplanes in part 135 

operation that would be affected by 

these proposals is relatively small. In 

the event changes to part 135 result in 

a greater number of affected airplanes 

operating under that part, the FAA will 

reassess the need to apply these 

proposed requirements to that part. 

The FAA believes that inclusion of 

certain rules under the new subparts 

will enhance the reader’s ability to 

readily identify rules pertinent to 

continued airworthiness. Unless stated 

otherwise, our purpose in moving 

requirements to the new subparts is to 

ensure easy visibility of those 

requirements applicable to the 

continued airworthiness of the airplane. 

We do not intend to change their legal 

effect in any other way. The new 

subparts are substantially the same and 

accordingly are not discussed separately 

here. Table 3 illustrates what proposed 

and existing requirements will be 

included in the new subparts. Each new 

subpart is titled ‘‘Continued 

Airworthiness and Safety 

Improvements.’’ The proposed new 

subparts consist of relocated, revised, 

and new regulations pertaining to 

continued airworthiness of the airplane. 

70940 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

17A part 91 operator would send the relevant 

information to either their principal inspector or 

Flight Standards District Office, as applicable. 

TABLE 3.—NEW SUBPARTS FOR PARTS 91, 121, 125, AND 129 

Part 91 new/relocated rules within 

proposed subpart K 

Part 121 new/relocated rules 

within proposed subpart Y 

Part 125 new/relocated rules 

within proposed subpart M 

Part 129 new/relocated rules 

within proposed subpart B 

§ 91.1501, Applicability (new) ........ § 121.901, Applicability ................. § 125.501, Applicability ................. § 129.101, Applicability. 

§ 91.1503, Reserved ...................... § 121.903, Reserved ..................... § 125.503, Reserved ..................... § 129.103, Reserved. 

§ 91.1505, fuel tank system maintenance program.§ 121.905, Electrical wiring interconnection systems (EWIS) 

maintenance program.

§ 125.505, Fuel tank system inspection program.§ 129.105, Electrical wiring interconnection systems (EWIS) 

maintenance program. 

§ 91.1507, Repairs assessment for 

pressurized fuselages (formerly 

§ 91.401(a)).

§ 121.907, Fuel tank system 

maintenance program.

§ 125.507, Repairs assessment 

for pressurized fuselages (formerly § 125.248(a)).

§ 129.107, Fuel tank system 

maintenance program. 

§ 91.1509, Reserved ...................... § 121.909, Reserved ..................... § 125.509, Reserved ..................... § 129.109, Reserved. 

§ 91.1511, Reserved ...................... § 121.911, Reserved ..................... § 125.511, Reserved ..................... § 129.111, Reserved. 

§ 121.913, Aging airplane inspections and records reviews (formerly § 121.368)........................................................ § 129.113, Supplemental inspections for U.S.-registered aircraft 

(formerly § 129.16). 

§ 121.915, Repairs assessment 

for pressurized fuselages (formerly § 121.370(a)).

....................................................... § 129.115, Repairs assessment 

for pressurized fuselages (formerly § 129.32(a)). 

§ 91.1513, Reserved ...................... § 121.917, Supplemental inspections (formerly § 121.370(a)........................................................ § 129.117, Aging airplane inspections and records reviews for 

U.S.-registered aircraft (formerly 

§ 129.33). 

1. Requirement to Install and Operate 

FRM, IMM or FIMM 

The proposed rules would prohibit 

certificate holders from operating any 

affected airplane after dates specified, 

unless IMM, FRM or FIMM, as 

applicable, are installed and operational 

for any fuel tank for which they are 

required. The safety objective of these 

proposed rules is to have the required 

modifications installed and operational 

at the earliest opportunity. 

The proposed rule would require that 

operators of the affected airplanes 

incorporate applicable maintenance 

program changes before returning an 

airplane to service after accomplishing 

any required modifications. 

For some of the affected airplanes, 

manufacturer compliance with the 

proposed requirements may not result 

in any design changes, but would result 

in development of airworthiness 

limitations in the form of maintenance 

actions, operational procedures, or 

CDCCL, as previously discussed. In 

these cases the affected operators would 

be required to incorporate these 

limitations within one year after their 

approval by the FAA oversight office. 

The FAA will inform the affected 

operators and principal inspectors of the 

availability of the approved information. 

Once an operator revises its 

maintenance or inspection program, it is 

important to make sure that later 

alterations to the airplane do not 

degrade the level of safety provided by 

these revisions. The proposed rules 

would require future applicants for 

approval of design changes to develop 

new airworthiness limitations for new 

auxiliary fuel tanks and other design 

changes affecting fuel tank flammability. 

To ensure that these airworthiness 

limitations are implemented, operators 

who incorporate these design changes 

into their airplanes would be required to 

revise their maintenance and inspection 

programs to incorporate the 

corresponding airworthiness 

limitations. 

Today’s proposal would require 

operators to submit the proposed 

maintenance and inspection program 

changes to their FAA Principal 

Inspector for review and approval.17

This review would include the 

integration of the applicable 

airworthiness limitations for the TC and 

any STC and field approved auxiliary 

fuel tank to ensure their consistency and 

compatibility in the maintenance or 

inspection program. Guidance will be 

provided to operators and principal 

inspectors regarding how to address any 

deviations that may be proposed by the 

affected operators from the information 

approved by the FAA oversight office. 

As airworthiness limitations, these 

cannot be changed without FAA 

approval, nor are they subject to 

maintenance review board or other 

maintenance program development 

processes. 

2. Authority To Operate With an 

Inoperative FRM, IMM or FIMM 

Generally, the FAA does not require 

operators to use or maintain equipment 

installed on airplanes prior to a uniform 

compliance date. In this proposal, we 

take a different approach. The safety 

advantages associated with a fuel tank 

system equipped with an FRM or IMM 

design, as modified by any FIMM, are so 

compelling that we propose requiring 

that operators use these systems as soon 

as they are available. We have 

accommodated the difficulties faced by 

operators in making the required design 

changes by providing a phased-in 

compliance schedule that extends up to 

seven years after the manufacturer’s 

compliance date for each model. 

Accordingly, an operator may not 

operate any airplane with fuel tanks 

equipped with FRM, IMM or FIMM, 

unless those systems are fully 

operational. The sole exception is when 

the systems are inoperative and the 

conditions and limitations specified in 

the operator’s Minimum Equipment List 

(MEL) are met. 

The method used to allow operation 

of an airplane when an FRM is 

inoperative would be to include the 

FRM dispatch relief in the FAAapproved MEL. The MEL contains a list 

of equipment that may be inoperative 

for a defined period of time. Under 

§ 91.213 and similar regulations, the 

airplane may be dispatched with 

inoperative equipment in accordance 

with the Master Minimum Equipment 

List (MMEL). 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70941 

18A copy of the AIA report is included in the 

docket for this rulemaking. 

The FAA Flight Operations 

Evaluation Board (FOEB) would 

establish the MMEL dispatch relief 

interval for an FRM based on data 

submitted by the applicant to the FAA. 

The expected MMEL dispatch relief 

interval is one of the contributing 

factors affecting the overall system 

reliability analyses that must be 

established early in the design of the 

FRM. The proposed requirements of 

Appendix K allow the designer to 

choose to design a highly reliable FRM 

and then request longer MMEL dispatch 

relief intervals when submitting their 

data to the FOEB. 

This proposal does not recommend 

the adoption of a specific MMEL 

dispatch inoperative interval at this 

time. However, the comments received 

from the NTSB on to the proposed 

special conditions for the Boeing 747 

indicate that the FRM should be treated 

like other non-redundant safety 

equipment, such as the flight data 

recorder. The recorders are allowed a 3- 

day MMEL inoperative interval. We 

specifically request public comment on 

the proposal to allow the current FOEB 

process to establish the MMEL interval 

rather than requiring a specific 

maximum interval. 

3. Compliance Schedule 

To achieve the safety benefits of this 

initiative, we believe it is necessary to 

have a mandatory schedule for phasing 

in the design changes rather than to rely 

solely on market forces to drive the 

production and availability of parts and 

normal maintenance scheduling for the 

installation of the FRM, IMM, or FIMM. 

Accordingly, this rule, if adopted, 

would require at least 50 percent of the 

affected airplanes be outfitted within 

four years after the relevant TC holder 

is required to comply with the proposed 

requirements. The remainder of the 

operator’s fleet would have to comply 

with the final rule within seven years 

after the specified date. The affected 

fleet would include those airplanes that 

have field or STC approved auxiliary 

fuel tanks. Certificate holders that 

operate only one airplane of an affected 

model would have to modify that 

airplane within the seven-year 

compliance period. 

The proposed compliance schedule of 

7 years after TC holders to develop 

service instructions, while long, should 

allow for the approval of the service 

instructions for IMM, FRM, or FIMM, 

manufacture of modification parts for a 

large fleet of airplanes, and 

accomplishment of the modifications 

with minimum disruption of normal 

maintenance schedules. Typically, fuel 

tanks are only accessed during heavy 

maintenance checks that are done on a 

schedule that is established during 

development of the maintenance 

program. The compliance dates 

proposed for the operational rules were 

developed to allow for the majority of 

the modifications to be done during 

these heavy maintenance checks. 

Introduction of FRM, IMM or FIMM 

outside of normally scheduled 

maintenance would increase the cost to 

the operators, because extra tank entry 

and airplane down time would be 

needed. 

Some airplane types or specific 

airplanes within an operator’s fleet may 

not be scheduled for normally 

scheduled maintenance, where the fuel 

tanks would be opened, during the 7- 

year compliance time after service 

instructions become available. These 

airplanes would require incorporation 

of modifications outside of the normally 

scheduled maintenance. We have 

determined the number of airplanes that 

would be affected is small and that 

further lengthening the compliance 

period would not achieve the safety 

benefits of this proposal in a timely 

way. Also, we anticipate that some of 

the upcoming ADs to address ignition 

source issues will occur in this time 

period and in some cases will require 

fuel tank entry. Compliance with the AD 

may provide additional opportunities 

for incorporating approved FRM, IMM 

or FIMM if not occurring during normal 

scheduled maintenance. These issues 

are further discussed in the regulatory 

evaluation. 

F. Additional Provisions 

1. Relationship of This Proposal to 

Aging Airplane Regulatory Initiatives 

As part of our broader review of 

several important initiatives comprising 

the Aging Airplane Program, we have 

revised certain compliance dates in 

existing rules and pending proposals so 

that operators can make required 

modifications during scheduled 

maintenance. Changing compliance 

dates affects our ability to expedite 

some aspects of this program but 

reduces the costs of the rules and 

proposals in place to deal with aging 

airplanes. Notice of these changes and a 

description of our Aging Airplane 

Program review appeared in the Federal 

Register on July 30, 2004 (69 FR 45936). 

In addition to this Fuel Tank 

Flammability Reduction proposal, the 

actions affected by these revisions 

include: 

• Aging Aircraft Program 

(Widespread Fatigue Damage (proposal), 

• Aging Airplane Safety (interim final 

rule), and 

• Enhanced Airworthiness Program 

for Airplane Systems/Fuel Tank Safety 

(proposal). 

Today’s proposal, if adopted, would 

also affect compliance with SFAR 88 

and potentially make it less costly. The 

safety reviews following the TWA 800 

accident led us to require that the fuel 

quantity indication system wiring 

entering high flammability tanks 

incorporate either adequate separation 

or energy limiting devices, known as 

transient suppression devices, on the 

Boeing 737 and 747 to protect the tank 

from ignition sources. As part of the 

safety reviews of SFAR 88, we have 

identified other models that likewise 

would need a transient suppression 

device. We have determined that if FRM 

are incorporated in high flammability 

fuel tanks, ADs requiring installation of 

devices to protect the fuel quantity 

system wiring will no longer be needed. 

We have not yet estimated the potential 

savings and have not included these 

savings in the current regulatory 

evaluation. We specifically request 

comments regarding the savings that 

would be achieved if electrical energy 

limiting devices were not required on 

wiring entering high flammability fuel 

tanks affected by this proposal. 

2. FAA Advisory Material 

We are developing extensive guidance 

material to supplement the proposed 

rule, including a revised AC 25.981–2 to 

include guidelines on conducting a fuel 

tank flammability exposure assessment 

using the Monte Carlo methodology and 

developing IMM and FRM. It will also 

include guidance on development of the 

airworthiness limitations section, 

confined space hazards and markings, 

documentation required by the FAA, 

and reporting methods. We have 

incorporated some comments on these 

topics from a group of specialists at the 

Aerospace Industries Association, 

which included airplane manufacturers, 

airline operators and manufacturers of 

inert gas generating equipment.18 The 

group provided advice on fuel tank 

inerting and use of the Monte Carlo 

methodology. We will invite public 

comments on the proposed ACs (which 

references the Monte Carlo User’s 

Manual) by separate notice published in 

the issue of the Federal Register. 

3. FAA Oversight Office 

We are also requiring affected persons 

to submit various compliance materials 

to the FAA Oversight Office, defined in 

proposed § 25.1803(c). The FAA 

Oversight Office is the aircraft 

70942 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

19Our worker safety requirements apply to 

confined spaces, which are partly or fully enclosed 

areas big enough for a worker to enter and perform 

assigned work and with limited or restricted means 

of entry or exit. Such areas are not designed for 

someone to work in regularly but for tasks such as 

inspection, cleaning, maintenance, and repair. 

(Reference U.S. Department of Labor Occupational 

Safety & Health Administration (OSHA), 29 CFR 

§ 1910.146(b).) This proposal would not 

significantly change the procedures used by 

maintenance personnel to enter fuel tanks and is 

not intended to conflict with existing government 

agency requirements (e.g., OSHA). 

certification office or office within the 

Transport Airplane Directorate having 

oversight responsibility for the relevant 

TC or STC, as delegated by the 

Administrator. For example, with 

respect to fuel-tank flammability issues, 

TC and STC holders must obtain 

approvals from the responsible office in 

the FAA’s Aircraft Certification Service. 

In other contexts, we have described the 

FAA office performing these functions 

as the ‘‘cognizant FAA office.’’

Table 4 lists the FAA offices that 

currently oversee issuance of TCs and 

amended TCs for manufacturers of large 

transport category airplanes. 

TABLE 4.—FAA OFFICES THAT OVERSEE TYPE CERTIFICATES

Airplane manufacturer FAA Oversight Office 

Aerospatiale .............................................................................................. Transport Airplane Directorate, International Branch. 

Airbus ........................................................................................................ Transport Airplane Directorate, International Branch. 

BAE ........................................................................................................... Transport Airplane Directorate, International Branch. 

Boeing ....................................................................................................... Seattle Aircraft Certification Office. 

Bombardier ............................................................................................... New York Aircraft Certification Office. 

Embraer .................................................................................................... Transport Airplane Directorate, International Branch. 

Fokker ....................................................................................................... Transport Airplane Directorate, International Branch. 

Gulfstream ................................................................................................ Atlanta Aircraft Certification Office. 

Lockheed .................................................................................................. Atlanta Aircraft Certification Office. 

Boeing/McDonnell-Douglas Corp ............................................................. Los Angeles Aircraft Certification Office. 

4. Workplace Safety Issues 

Because we would require that 

maintenance personnel be given access 

to FRM installations, the proposal could 

increase occupational safety risks for 

these personnel. A large percentage of 

the work involved in properly 

inspecting and modifying airplane fuel 

tanks and their associated systems must 

be done in the interior of the tanks. 

Performing the necessary tasks requires 

inspection and maintenance personnel 

to physically enter the tank, where 

environmental hazards exist. These 

hazards exist in any fuel tank 

(regardless of whether a nitrogen 

inerting system is installed) and include 

fire and explosion, toxic and irritating 

chemicals, oxygen deficiency, and the 

confinement to the fuel tank itself. To 

prevent related injuries, operator and 

repair station maintenance 

organizations have developed specific 

procedures for identifying, controlling, 

or eliminating the hazards of fuel-tank 

entry. In addition, government agencies 

have adopted safety requirements for 

use when entering fuel tanks and other 

confined spaces. These same procedures 

would be applied to the reduced oxygen 

environment likely to be present in an 

inerted fuel tank. 

Introduction of nitrogen enriched air 

within the fuel tanks and the possibility 

of nitrogen enriched air in 

compartments adjacent to the fuel tanks 

if leakage occurs creates additional risk. 

Lack of oxygen in these areas could be 

hazardous to maintenance personnel, 

the passengers, or flight crew. Existing 

certification requirements address these 

hazards. This proposal requires 

markings to emphasize the potential 

hazards associated with confined spaces 

and areas where a hazardous 

atmosphere could be present as a result 

specifically of the addition of FRM. We 

would require that the access doors and 

panels to the fuel tanks with FRMs and 

to any other enclosed areas that could 

contain hazardous atmosphere under 

either normal conditions or failure 

conditions be permanently stenciled, 

marked, or placarded to warn of 

hazards. 

Fuel tanks are confined spaces 19 and 

contain high concentrations of fuel 

vapors that must be exhausted from the 

fuel tank before entry. Other precautions 

such as measurement of oxygen 

concentrations before entering a fuel 

tank are already required. Addition of 

the FRM that utilizes inerting may result 

in reduced oxygen concentrations due 

to leakage of the system in locations in 

the airplane where service personnel 

would not expect it. These gases may be 

under pressure because of the FRM 

design, and any hazards associated with 

working in adjacent spaces near the 

opening should be identified in the 

marking of the opening to the confined 

space. 

Designs currently under consideration 

locate the FRM in the fairing below the 

center wing fuel tank. Access to these 

areas is obtained by opening doors or 

removing panels, which could allow 

some ventilation of the spaces adjacent 

to the FRM. But this may not be enough 

to avoid creating a hazard. Therefore, 

unless the design eliminates this hazard, 

we intend that marking be provided to 

warn service personnel of possible 

hazards associated with the reduced 

oxygen concentrations in the areas 

adjacent to the FRM. Appropriate 

markings would be required for all 

inerted fuel tanks, tanks adjacent to 

inerted fuel tanks and all fuel tanks 

communicating with the inerted tanks 

via plumbing. The plumbing includes, 

but is not limited to, plumbing for the 

vent system, fuel feed system, refuel 

system, transfer system and cross-feed 

system. The markings should also be 

stenciled on the external upper and 

lower surfaces of the inerted tank 

adjacent to any openings, to ensure 

maintenance personnel understand the 

possible contents of the fuel tank. 

Advisory Circular 25.981–2 will 

provide additional guidance regarding 

markings and placards. 

IV. Rulemaking Analyses and Notices 

Authority for This Rulemaking 

The FAA’s authority to issue rules 

regarding aviation safety is found in 

Title 49 of the United States Code. 

Subtitle I, Section 106, describes the 

authority of the FAA Administrator. 

Subtitle VII, Aviation Programs, 

describes in more detail the scope of the 

agency’s authority. This rulemaking is 

promulgated under the authority 

described in Subtitle VII, Part A, 

Subpart III, Section 44701, ‘‘General 

requirements.’’ Under that section, the 

FAA is charged with promoting safe 

flight of civil aircraft in air commerce by 

prescribing. 

• Minimum standards required in the 

interest of safety for the design and 

performance of aircraft; 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70943 

• Regulations and minimum 

standards in the interest of safety for 

inspecting, servicing, and overhauling 

aircraft; and 

• Regulations for other practices, 

methods, and procedures the 

Administrator finds necessary for safety 

in air commerce. 

This regulation is within the scope of 

that authority because it prescribes—

• New safety standards for the design 

of transport category airplanes, and 

• New requirements necessary for 

safety for the design, production, 

operation, and maintenance of those 

airplanes, and for other practices, 

methods and procedures relating to 

those airplanes. 

Paperwork Reduction Act 

This proposal contains the following 

new information collection 

requirements. As required by the 

Paperwork Reduction Act of 1955 (44 

U.S.C. 3507(d)), the Department of 

Transportation has sent the information 

requirements associated with this 

proposal to the Office of Management 

and Budget for its review. 

Title: Transport Category Airplane 

Fuel Tank Flammability Reduction 

Safety Improvements. 

Summary: This proposal would 

require certain certificate holders to 

develop means to reduce the 

flammability of high flammability 

exposure fuel tanks on certain large 

turbine-powered transport category 

airplanes. In addition, this proposal 

requires operators of the affected 

airplanes with high flammability 

exposure fuel tanks to incorporate FRM. 

The current requirements for fuel tank 

flammability exposure for new designs 

would be revised to add requirements 

for inerting systems if inerting is used 

to minimize flammability exposure. 

This proposal also proposes to expand 

the coverage of part 25 to include 

requirements that must be complied 

with by current holders of these 

certificates. Certificate holders would be 

required to provide a quarterly report to 

the FAA that contains reliability data for 

the FRM. There is no specific reporting 

requirement for operators. Data 

collected by the certificate holders from 

operators would be obtained through 

normal business agreements. 

Proposed subpart I would also require 

that TC holders submit to the FAA a 

plan detailing how they intend to 

comply with its requirements. This 

information would be used by the FAA 

to assist the TC holder in complying 

with requirements. The compliance 

plan would be necessary to ensure that 

TC holders fully understand the 

requirements, correct any deficiencies 

in planning in a timely manner, and are 

able to provide the information needed 

by the operators for the operators’

timely compliance with the rule. 

Reporting: When scheduled or 

unscheduled maintenance and 

inspections are performed, including 

tasks that are not identified as ALI or 

Certification Maintenance 

Requirements, the operators are only 

required to report specific discrepancies 

and corrective actions in accordance 

with § 121.703. This proposal would not 

mandate any additional reporting above 

the current requirements for ALI by the 

operators. We do not intend that 

operators report to the FAA the results 

of routine inerting system operational 

checks, or discrepancies found . 

The proposed reporting requirement 

applies to applicants and holders of the 

affected certificates. There is no 

proposed additional requirement within 

this rulemaking for operators to report 

FRM reliability information. We intend 

for certificate holders to gather the 

needed data from operators using 

existing reporting systems that are 

currently used for airplane 

maintenance, reliability and warranty 

claims. The operators would provide 

this information through existing or new 

business arrangements between the 

certificate holders and the airlines. 

Use of: This proposal would support 

the information needs of the FAA in 

approving design approval holder and 

operator compliance with the proposed 

rule. 

Respondents (including number of): 

The likely respondents to this proposed 

information requirement are the affected 

type certificate holders such as Boeing, 

Airbus and several auxiliary fuel tank 

manufacturers. 

Frequency: The proposal would 

require the certificate holders to submit 

a report to the FAA once each quarter 

for a period up to 5 years. 

Average Annual Burden Estimate: 

The burden would consist of the work 

necessary to: 

• Develop the design and the data for 

STCs to install fuel tank inerting 

systems, 

• Develop and incorporate a 

maintenance plan into the existing 

maintenance programs, 

• Record the results of the installation 

and maintenance activities. 

The largest paperwork burden would be 

a one-time effort (spread over 3 years) 

associated with the STC applications. 

This one-time total burden would be as 

follows: 

Documents required to show compliance with the proposed rule One-time pages 

Present value 

discounted cost 

(in millions of 

$2005) 

Specifications for Fuel Tank STC .................................................................................................................... 8,000 2.7 

Manuals (Flight Manuals, Operations, and Maintenance) for Fuel Tank STC ............................................... 12,000 2.7 

Production for Fuel Tank STC ......................................................................................................................... 500 0.4 

Documentation for FAA/EASA Certification .................................................................................................... 1,000 13.4 

Total .......................................................................................................................................................... 21,500 19.2 

The yearly burden for each of the 3 

years would have a present value of 

about $6.4 million and involve 7,167 

pages. 

This proposed rulemaking would 

result in a minimal annual 

recordkeeping and reporting burden. All 

records that would be generated to 

verify the installation, to record any fuel 

tank system inerting failures, and to 

record any maintenance would use 

forms currently required by the FAA. 

The FAA computed the annual 

recordkeeping (Total Pages) burden by 

analyzing the necessary paperwork 

requirements needed to satisfy each 

process of the proposed rulemaking. 

The agency is seeking comments to—

• Evaluate whether the proposed 

information requirement is necessary for 

the proper performance of the roles of 

the agency, including whether the 

information will have practical utility; 

• Evaluate the accuracy of the 

agency’s estimate of the burden; 

• Improve the quality, utility, and 

clarity of the information to be 

collected; and 

• Minimize the burden of the 

collection of information on those who 

are to respond using appropriate 

automated, electronic, mechanical, or 

70944 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

20The estimated cost for aviation fuel is based on 

both the FAA’s 2005 forecast and the Department 

of Energy Information Administration’s forecast 

‘‘Annual Energy Outlook with Projections to 2025’’

(2005). Should these forecasts change prior to the 

publication of the final rule, if any, we will use the 

updated number. However, we do not expect 

changes in the forecast cost of aviation fuel to have 

a large impact on the overall cost of this 

rulemaking. 

other technological collection 

techniques or other forms of information 

technology. 

Individuals and organizations may 

submit comments to the FAA on the 

information collection requirement by 

February 21, 2006. You should send 

your comments to the address listed in 

the ADDRESSES section of this document. 

Under the Paperwork Reduction Act 

of 1995, (5 CFR 1320.8(b)(2)(vi)), an 

agency may not conduct or sponsor, and 

a person is not required to respond to, 

a collection of information unless it 

displays a currently valid OMB control 

number. The OMB control number for 

this information collection will be 

published in the Federal Register, after 

the Office of Management and Budget 

approves it. 

International Compatibility 

In keeping with U.S. obligations 

under the Convention on International 

Civil Aviation, it is FAA policy to 

comply with International Civil 

Aviation Organization (ICAO) Standards 

and Recommended Practices to the 

maximum extent practicable. The FAA 

has determined that there are no ICAO 

Standards and Recommended Practices 

that correspond to these proposed 

regulations. 

Regulatory Evaluation, Regulatory 

Flexibility Determination, International 

Trade Assessment, and Unfunded 

Mandates Assessment 

Regulatory Evaluation 

This portion of the preamble 

summarizes our analysis of the 

economic impacts of this NPRM. It also 

includes summaries of the initial 

regulatory flexibility determination. We 

suggest readers seeking greater detail 

read the full regulatory evaluation, a 

copy of which we have placed in the 

docket for this rulemaking. 

Changes to Federal regulations must 

undergo several economic analyses. 

First, Executive Order 12866 directs that 

each Federal agency shall propose or 

adopt a regulation only upon a reasoned 

determination that the benefits of the 

intended regulation justify its costs. 

Second, the Regulatory Flexibility Act 

of 1980 requires agencies to analyze the 

economic impact of regulatory changes 

on small entities. Third, the Trade 

Agreements Act (19 U.S.C. 2531–2533) 

prohibits agencies from setting 

standards that create unnecessary 

obstacles to the foreign commerce of the 

United States. In developing U.S. 

standards, this Trade Act requires 

agencies to consider international 

standards and, where appropriate, to be 

the basis of U.S. standards. Fourth, the 

Unfunded Mandates Reform Act of 1995 

(Pub. L. 104–4) requires agencies to 

prepare a written assessment of the 

costs, benefits, and other effects of 

proposed or final rules that include a 

Federal mandate likely to result in the 

expenditure by State, local, or tribal 

governments, in the aggregate, or by the 

private sector, of $100 million or more 

annually (adjusted for inflation). 

In conducting these analyses, we 

determined this rule: (1) Is a ‘‘significant 

regulatory action’’ as defined in section 

3(f) of Executive Order 12866, and is 

‘‘significant’’ as defined in DOT’s 

Regulatory Policies and Procedures; (2) 

would have a significant economic 

impact on a substantial number of small 

entities; (3) has a neutral international 

trade impact; and (4) does not impose 

an unfunded mandate on state, local, or 

tribal governments, or on the private 

sector. These analyses, available in the 

docket, are summarized as follows. 

Total Benefits and Costs of This 

Rulemaking 

We estimated that the proposed rule 

would prevent an expected 4 

catastrophic passenger accidents over 

the analysis period. If all accidents 

happened in-flight, the present value 

total benefit would be of $490 million. 

The model of fuel tank flammability risk 

suggests an 8 percent probability that 

the explosion may occur on the ground. 

Assuming this rate of ground 

explosions, the present value of the total 

benefit would be about $460 million. 

This estimate is based on an average 

number of occupants per airplane. If the 

first of the prevented accidents would 

occur on a large passenger capacity 

airplane, like the Airbus A380 or TWA–

800 Boeing Model 747, the quantified 

benefit of preventing one accident could 

exceed the present value costs. In 

addition, another fuel tank explosion 

would have a negative impact on public 

confidence in air travel safety, and, on 

the subsequent demand for air travel. 

Table 1 displays the present value 

compliance costs by major element for 

the existing air carrier fleet and for 

airplanes manufactured over the next 25 

years and operated over the next 50 

years to be $919 million. 

TABLE 1.—PRESENT VALUE COSTS OF

COMPLIANCE (2006–2055) 

[In millions 2005 $] 

Source of cost 

Present value 

of the compliance costs 

Engineering Redesign ........ $64 

Retrofitting Costs ................ 377 

Production Costs ................ 133 

TABLE 1.—PRESENT VALUE COSTS OF

COMPLIANCE (2006–2055)—Continued 

[In millions 2005 $] 

Source of cost 

Present value 

of the compliance costs 

Operational Costs ............... 345 

Total ............................. 919 

Who is Potentially Affected By This 

Rulemaking 

Boeing, Airbus, all operators flying 

U.S.-registered Boeing and Airbus 

airplanes, and holders of fuel tank 

supplemental type certificates (STCs). 

Cost Assumptions and Sources of 

Information 

Period of analysis is 2006–2055. 

For 2008–2030, we evaluated the 

costs and benefits for all airplanes that 

would have fuel tank inerting systems. 

This includes airplanes that would be 

retrofitted between 2008 and 2015 and 

production airplanes manufactured 

between 2008 and 2030. 

For 2031–2055, we evaluated the 

costs and benefits for all airplanes that 

had fuel tank inerting systems and are 

expected to be in service in 2030. No 

airplanes are added after that date. This 

time allows for all of the airplanes in 

this evaluation to complete their 

productive lives in U.S. aviation and be 

retired. 

Based on Boeing’s assertion that their 

production airplanes will have fuel tank 

inerting installed by 2008, we do not 

include Boeing production airplanes 

built during and after 2008 in either the 

cost or the benefits estimates. 

• Final rule would be effective 

January 1, 2006. 

• Discount rate is 7 percent. 

• Fully burdened labor rate for an 

aviation engineer is $125 an hour. 

• Fully burdened labor rate for an 

aviation mechanic is $85 an hour. 

• 3,804 airplanes would be retrofitted 

between 2008 and 2016. 

• No airplane scheduled to be retired 

before 2016 would be retrofitted. 

• Cost of aviation fuel is $1.00 per 

gallon.20

• The type of accident that would be 

prevented is a catastrophic accident in 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70945 

21These four accidents represent the expected 

average. Based on the Poisson distribution and a 

past average of one accident every 60 million flight 

hours for airplanes with a heated center wing fuel 

tank there is a 37 percent chance that there would 

be 5 or more such accidents. 

which all die and the airplane is 

destroyed. 

• Special Federal Air Regulation 

(SFAR) 88 would prevent 50 percent of 

the future fuel tank explosions. (See 

‘‘History of Industry and Government 

Actions in Response to Fuel Tank 

Explosions’’ in the full regulatory 

evaluation located within the docket file 

for this proposal) 

• Boeing and Airbus airplanes have 

equal risk of an explosion. 

• The explosion rate calculation does 

not include explosions caused by 

terrorist activity. 

• An explosion is estimated to occur 

every 60 million hours of flight by 

heated center wing tank airplanes. 

• The value of a statistical fatality 

averted is $3 million. 

• An average of 140 passengers and 

crew are on a Boeing or Airbus airplane. 

• The cost to investigate a 

catastrophic accident is $8 million. 

• The average value of property loss 

and fatalities located on the ground is 

$500,000 to $1 million. 

We obtained data from two Aviation 

Rulemaking Advisory Committee 

(ARAC) working groups, Boeing, and 

Airbus. 

Finally, we request comments and 

information about all of our 

assumptions, values, and results. In 

particular, we request information 

concerning the potential cost savings 

from not requiring airplanes to install 

transient suppression devices. We also 

request that you provide documentation 

for the comments. 

Estimated Benefits 

We estimated the proposed rule 

would prevent four fuel tank explosions 

over the next 50 years, for a present 

value total benefit of $490 million.21

The undiscounted benefits from 

preventing one average-sized airplane 

catastrophic accident are about $500 

million, assuming $3 million for the 

value of a prevented fatality. If the value 

of prevented fatality is $5.5 million, the 

undiscounted benefits are about $890 

million. 

The model of fuel tank flammability 

risk suggests an 8 percent probability 

that an airplane would explode on the 

runway, with an average of four 

fatalities. Under this scenario, the 

average benefit would be about $60 

million. Assuming an 8 percent chance 

on an accident while the airplane is still 

on the ground would reduce the total 

benefit, in present value, by $30 million 

to be about $460 million. 

Costs of This Rulemaking 

The undiscounted total costs for the 

analysis period 2006–2055 for all 

airplanes would be about $2.279 billion, 

with a present value of $919 million. 

The undiscounted passenger airplane 

costs would be about $2.018 billion 

with a present value of $809 million. 

However, there is a potential cost 

reduction factor. If we enact a fuel tank 

flammability reduction rule, we would 

not require transient suppression 

devices and we would allow airlines 

that have installed them to remove 

them. We request information on 

potential cost savings from this action. 

Analysis of the Proposed Rule and 

Alternatives, All Airplanes (2006–2055) 

In all of the tables that follow, the 

results for the base case are found in the 

first row. As shown in Table 2, using a 

discount rate of 7 percent, $3 million for 

a prevented fatality, and an SFAR 88 

effectiveness rate of 50 percent, the 

proposed rule benefits would be about 

$424 million less (54 percent) than the 

costs. Increasing the value of a 

prevented fatality to $5.5 million would 

make the benefits about 94 percent of 

the costs. At an SFAR effectiveness rate 

of 25 percent, the benefits would be 80 

percent of the costs for a $3 million 

value of a prevented fatality, but would 

be 41 percent greater than the costs for 

a $5.5 million value of a prevented 

fatality. 

For a 3 percent discount rate, the 

proposed rule benefits would be greater 

than the costs at an SFAR effectiveness 

rate of 25 percent. At 50 percent, the 

value of a fatality would need to be $5.5 

million for the benefits to be greater 

than the costs—a $3 million value 

would result in the benefits being about 

three quarters of the costs. 

At an SFAR 88 effectiveness rate of 75 

percent, the proposed rule benefits 

would be less than the compliance costs 

under any combination of discount rate 

and value of a prevented fatality. 

TABLE 2.—PRESENT VALUES OF THE ESTIMATED BENEFITS AND COSTS FOR ALL AIRPLANES BY DISCOUNT RATE, VALUE

OF A PREVENTED FATALITY, AND SFAR 88 EFFECTIVENESS RATE

[Values in million of 2005 dollars] 

Discount rate 

(percent) 

Value of 

fatality 

SFAR 88 

effectiveness 

(percent) 

Present values Benefit/cost 

ratio 

Benefits Costs (percent) 

7 ............................................................................... $3 50 $495 $919 54 

7 ............................................................................... 5 .5 50 861 919 94 

7 ............................................................................... 3 25 743 919 81 

7 ............................................................................... 5 .5 25 1,292 919 141 

7 ............................................................................... 3 75 248 919 27 

7 ............................................................................... 5 .5 75 431 919 47 

3 ............................................................................... 3 50 1,011 1,312 77 

3 ............................................................................... 5 .5 50 1,774 1,312 135 

3 ............................................................................... 3 25 1,517 1,312 116 

3 ............................................................................... 5 .5 25 2,662 1,312 203 

3 ............................................................................... 3 75 506 1,312 39 

3 ............................................................................... 5 .5 75 888 1,312 68 

Passenger Airplanes (2006–2055) 

As shown in Table 3, using a discount 

rate of 7 percent, a $3 million value for 

a prevented fatality, and an SFAR 88 

effectiveness rate of 50 percent, we 

estimated that the proposed rule 

benefits for passenger airplanes would 

be about $313 million less than the 

costs. Increasing the value of a 

prevented fatality to $5.5 million 

indicates the proposed rule benefits 

would be greater than the costs by about 

6 percent for passenger airplanes. At an 

SFAR effectiveness rate of 25 percent, 

70946 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

the proposed rule benefits would be less 

than the costs for a $3 million value of 

a prevented fatality (benefits would be 

92 percent of costs), but would be 

greater than the costs for a $5.5 million 

value of a prevented fatality (benefits 

would be 60 percent greater than the 

costs) for passenger airplanes. 

For a 3 percent discount rate, the 

proposed rule benefits for passenger 

airplanes would be greater than their 

costs at an SFAR effectiveness rate of 25 

percent. At 50 percent, the value of a 

fatality would need to be $5.5 million 

for the benefits to be greater than the 

costs—a $3 million value would result 

in the benefits would be about 87 

percent of the costs. 

At an SFAR 88 effectiveness rate of 75 

percent, the proposed rule benefits 

would be less than the costs for 

passenger airplanes under any 

combination of discount rate and value 

of a prevented fatality. 

TABLE 3.—PRESENT VALUES OF THE ESTIMATED BENEFITS AND COSTS FOR ALL PASSENGER AIRPLANES BY DISCOUNT

RATE, VALUE OF A PREVENTED FATALITY, AND SFAR 88 EFFECTIVENESS RATE

[Values in million of 2005 dollars] 

Discount rate 

(percent) 

Value of 

fatality 

SFAR 88 

effectiveness 

(percent) 

Present values Benefit/cost 

ratio 

Benefits Costs (percent) 

7 ............................................................................... $3 50 $495 $808 61 

7 ............................................................................... 5 .5 50 861 808 106 

7 ............................................................................... 3 25 743 808 92 

7 ............................................................................... 5 .5 25 1,292 808 160 

7 ............................................................................... 3 75 248 808 31 

7 ............................................................................... 5 .5 75 431 808 53 

3 ............................................................................... 3 50 1,011 1,157 87 

3 ............................................................................... 5 .5 50 1,774 1,157 153 

3 ............................................................................... 3 25 1,517 1,157 131 

3 ............................................................................... 5 .5 25 2,662 1,157 230 

3 ............................................................................... 3 75 506 1,157 44 

3 ............................................................................... 5 .5 75 888 1,157 77 

Retrofitted Passenger Airplanes (2006–

2037) 

As shown in Table 4, if the SFAR 88 

effectiveness rate is 75 percent, the 

proposed rule benefits would not be 

greater than the costs for retrofitted 

passenger airplanes under any 

combination of discount rate and value 

of a prevented fatality. 

Using a discount rate of 7 percent, a 

$3 million value for a prevented fatality, 

and an SFAR 88 effectiveness rate of 50 

percent, the proposed rule benefits for 

retrofitted passenger airplanes would be 

about $217 million less than the costs. 

Increasing the value of a prevented 

fatality to $5.5 million indicates the 

proposed rule benefits would be greater 

than the costs by about 4 percent for 

retrofitted passenger airplanes. At an 

SFAR effectiveness rate of 25 percent, 

the proposed rule benefits would be less 

than the costs for a $3 million value of 

a prevented fatality (benefits would be 

88 percent of costs), but would be 

greater than the costs for a $5.5 million 

value of a prevented fatality (benefits 

would be 55 percent greater than the 

costs) for retrofitted passenger airplanes. 

For a 3 percent discount rate, the 

proposed rule benefits for retrofitted 

passenger airplanes would be greater 

than their costs at an SFAR effectiveness 

rate of 25 percent. 

At 50 percent, the value of a fatality 

would need to be $5.5 million for the 

benefits to be greater than the costs—a 

$3 million value would result in the 

benefits would be about three quarters 

percent of the costs. 

At an SFAR 88 effectiveness rate of 75 

percent, the proposed rule benefits 

would be less than the costs for 

retrofitted passenger airplanes under 

any combination of discount rate and 

value of a prevented fatality. 

TABLE 4.—PRESENT VALUES OF THE ESTIMATED BENEFITS AND COSTS FOR ALL RETROFITTED PASSENGER AIRPLANES

BY DISCOUNT RATE, VALUE OF A PREVENTED FATALITY, AND SFAR 88 EFFECTIVENESS RATE

[Values in million of 2005 dollars] 

Discount rate 

(percent) 

Value of 

fatality 

SFAR 88 

effectiveness 

(percent) 

Present values Benefit/cost 

ratio 

Benefits Costs (percent) 

7 ............................................................................... $3 50 $313 $530 59 

7 ............................................................................... 5 .5 50 549 530 104 

7 ............................................................................... 3 25 469 530 88 

7 ............................................................................... 5 .5 25 824 530 155 

7 ............................................................................... 3 75 156 530 29 

7 ............................................................................... 5 .5 75 275 530 52 

3 ............................................................................... 3 50 557 750 74 

3 ............................................................................... 5 .5 50 992 750 132 

3 ............................................................................... 3 25 836 750 111 

3 ............................................................................... 5 .5 25 1,488 750 198 

3 ............................................................................... 3 75 279 750 37 

3 ............................................................................... 5 .5 75 496 750 66 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70947 

Production Passenger Airplanes (2006–

2055) 

We determined that all of the 

retrofitted airplanes would have been 

retired from U.S. service by 2038. As 

shown in Table 5, using a discount rate 

of 7 percent, a $3 million value for a 

prevented fatality, and an SFAR 88 

effectiveness rate of 50 percent, the 

proposed rule benefits for production 

passenger airplanes would be about 

$196 million less than the costs—about 

65 percent of the costs. Increasing the 

value of a prevented fatality to $5.5 

million indicates that the proposed rule 

benefits would be greater than the costs 

by about 12 percent for production 

passenger airplanes. 

At an SFAR effectiveness rate of 25 

percent, the proposed rule benefits for 

production airplanes would be greater 

than their costs for both combinations of 

discount rates and values of a prevented 

fatality. 

At a 3 percent discount rate, the 

proposed rule benefits for production 

airplanes would be greater than their 

costs at an SFAR effectiveness rate of 

either 25 percent or 50 percent. 

At an SFAR 88 effectiveness rate of 75 

percent, the proposed rule benefits 

would be less than the costs for 

production passenger airplanes under 

any combination of discount rate and 

value of a prevented fatality—although 

they would be 96 percent of the costs if 

a 3 percent discount rate and a $5.5 

million value of a prevented fatality 

were used. 

TABLE 5.—PRESENT VALUES OF THE ESTIMATED BENEFITS AND COSTS FOR ALL PRODUCTION PASSENGER AIRPLANES BY

DISCOUNT RATE, VALUE OF A PREVENTED FATALITY, AND SFAR 88 EFFECTIVENESS RATE

[Values in million of 2005 dollars] 

Discount rate 

(percent) 

Value of 

fatality 

SFAR 88 

effectiveness 

(percent) 

Present values 

Benefits Costs 

Benefit/cost 

ratio 

(percent) 

7 ............................................................................... $3 50 $182 $278 65 

7 ............................................................................... 5 .5 50 312 278 112 

7 ............................................................................... 3 25 273 278 98 

7 ............................................................................... 5 .5 25 468 278 168 

7 ............................................................................... 3 75 91 278 33 

7 ............................................................................... 5 .5 75 156 278 56 

3 ............................................................................... 3 50 454 407 112 

3 ............................................................................... 5 .5 50 783 407 192 

3 ............................................................................... 3 25 681 407 167 

3 ............................................................................... 5 .5 25 1,175 407 289 

3 ............................................................................... 3 75 227 407 56 

3 ............................................................................... 5 .5 75 392 407 96 

Alternative One: Apply the Proposed 

Rule Only to Production Airplanes—

Exclude Retrofitting Requirements 

As shown in Table 6, the benefit-cost 

ratios of the present values are lower for 

retrofitted airplanes than they are for 

production airplanes. However, at a 7 

percent discount rate, the ratios are very 

close. Using the standard values, there 

is only a 6-percentage point difference 

(about 10 percent) between the 59 

percent ratio for retrofitted passenger 

airplanes and the 65 percent ratio for 

production passenger airplanes. This 

same result is observed for all benefit/ 

cost ratios calculated using a 7 percent 

discount rate. The difference becomes 

more pronounced (about 30 percent to 

40 percent) when a 3 percent discount 

rate is used. This apparent conflict is 

resolved by noting that a far greater 

percentage of the total benefits for 

retrofitted airplanes would occur in the 

more immediate future than it would for 

production airplanes that have more of 

its benefits occurring farther out in time. 

Thus, a lower discount rate has a greater 

positive impact (relatively) on present 

value calculations for longer-term 

benefits than for shorter-term benefits. 

That is, retrofitted airplanes would 

incur the vast bulk of these airplanes 

flight hours and the relatively greater 

overall risk until about 2030. 

TABLE 6.—BENEFIT-COST PRESENT VALUES RATIOS FOR PASSENGER AIRPLANES BY DISCOUNT RATE, VALUE OF A

PREVENTED FATALITY, SFAR 88 EFFECTIVENESS RATE, AND TYPE OF FUEL TANK INERTING INSTALLATION

[Values in million of 2005 dollars] 

Discount rate 

(percent) 

Value of 

fatality 

SFAR 88 

effectiveness 

(percent) 

Benefit/cost ratios 

Retrofitted 

(percent) 

Production 

(percent) 

Productionretrofitted 

(percent) 

7 ............................................................................... $3 50 59 65 6 

7 ............................................................................... 5 .5 50 104 112 8 

7 ............................................................................... 3 25 88 98 10 

7 ............................................................................... 5 .5 25 155 168 13 

7 ............................................................................... 3 75 29 33 4 

7 ............................................................................... 5 .5 75 52 56 4 

3 ............................................................................... 3 50 74 112 38 

3 ............................................................................... 5 .5 50 132 192 60 

3 ............................................................................... 3 25 111 167 56 

3 ............................................................................... 5 .5 25 198 289 91 

3 ............................................................................... 3 75 37 56 19 

70948 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

TABLE 6.—BENEFIT-COST PRESENT VALUES RATIOS FOR PASSENGER AIRPLANES BY DISCOUNT RATE, VALUE OF A

PREVENTED FATALITY, SFAR 88 EFFECTIVENESS RATE, AND TYPE OF FUEL TANK INERTING INSTALLATION—Continued 

[Values in million of 2005 dollars] 

Discount rate 

(percent) 

Value of 

fatality 

SFAR 88 

effectiveness 

(percent) 

Benefit/cost ratios 

Retrofitted 

(percent) 

Production 

(percent) 

Productionretrofitted 

(percent) 

3 ............................................................................... 5 .5 75 66 96 30 

In light of these results, we 

determined that the benefit-cost analysis 

does not justify requiring production 

airplanes to have fuel tank inerting 

systems while not requiring these 

systems on retrofitted airplanes. Both 

airplanes need these systems. 

Alternative Two: Include Cargo 

Airplanes in the Proposed Rule 

As shown by Tables 2 and 3, 

including cargo airplanes in the 

proposed rule would have no affect on 

the present value of the proposed rule’s 

quantified benefits and it would 

increase the cost by $111 million (a 12 

percent increase). Using a discount rate 

of 7 percent, a $3 million value for a 

prevented fatality and an SFAR 88 

effectiveness rate of 50 percent, the 

benefit-cost ratio would decrease from 

61 percent to 53 percent. 

Cost Benefit Summary 

We believe the benefits of preventing 

four expected fuel tank explosions over 

fifty years justify the compliance cost. 

While our model predicts one accident 

every 60 million flight hours of fleet 

operation and a total of four prevented 

accidents within the analysis period, 

there is a nearly 40 percent probability 

of five or more accidents. In addition, 

these accidents could occur on airplanes 

with larger passenger capacity than the 

average assumed in this analysis, and 

they could occur sooner than we 

forecast. If this rule prevents two 

accidents comparable to the TWA 

accident with 230 fatalities, then 

preventing two of these accidents would 

produce estimated undiscounted 

benefits of $2.5 billion and would 

justify the undiscounted compliance 

cost of this proposed rule. Finally, we 

did not include the potential losses 

associated with the likely disruption to 

commercial aviation resulting from an 

in-flight explosion. Such an explosion 

could immediately raise a terrorism 

concern. In the preliminary regulatory 

evaluation, we estimate that the costs 

associated with a potential disruption 

could cost approximately $5 billion per 

accident. 

Regulatory Flexibility Determination 

The Regulatory Flexibility Act of 1980 

(RFA) establishes ‘‘as a principle of 

regulatory issuance that agencies shall 

endeavor, consistent with the objective 

of the rule and of applicable statutes, to 

fit regulatory and informational 

requirements to the scale of the 

business, organizations, and 

governmental jurisdictions subject to 

regulation.’’ To achieve that principle, 

the RFA requires agencies to solicit and 

consider flexible regulatory proposals 

and to explain the rationale for their 

actions. The RFA covers a wide-range of 

small entities, including small 

businesses, not-for-profit organizations 

and small governmental jurisdictions. 

Agencies must perform a review to 

determine whether a proposed or final 

rule will have a significant economic 

impact on a substantial number of small 

entities. If the agency determines that it 

will, the agency must prepare a 

regulatory flexibility analysis as 

described in the Act. 

The proposed rule would require all 

Boeing and Airbus airplane operators, 

including about 18 small business 

operators, to retrofit their airplanes. We 

believe that this proposed rule would 

have a significant impact on a 

substantial number of small entities. 

Accordingly, an initial regulatory 

flexibility analysis, as required by the 

RFA, is included as part of the Initial 

Regulatory Analysis that is in the 

docket. 

International Trade Impact Assessment 

This proposed rule would impose the 

same costs on Boeing and Airbus Nregistered airplanes operated by 

domestic entities. It would also impose 

costs on the airplanes and the 

operations of domestic entities flying 

internationally. However, foreign 

entities flying into the United States 

would not be affected by the proposed 

rule and would have a competitive 

advantage in competing for 

international business with U.S. 

domestic carriers. Based on the safety 

issues involved, we determined that 

these costs are acceptable to obtain the 

required level of air travel safety. 

Unfunded Mandates Reform Act 

The Unfunded Mandates Reform Act 

of 1995 (the Act) is intended, among 

other things, to curb the practice of 

imposing unfunded Federal mandates 

on State, local, and tribal governments. 

Title II of the Act requires each Federal 

agency to prepare a written statement 

assessing the effects of any Federal 

mandate in a proposed or final agency 

rule that may result in an expenditure 

of $100 million or more (adjusted 

annually for inflation) in any one year 

by State, local, and tribal governments, 

in the aggregate, or by the private sector; 

such a mandate is deemed to be a 

‘‘significant regulatory action.’’ We 

currently use an inflation-adjusted value 

of $120.7 million in lieu of $100 

million. 

We note that the rule would impose 

a significant private sector cost in 2014 

and 2015, as the estimated 

undiscounted retrofitting cost would be 

about $110 million, which has a present 

value of about $70 million. Thus, this 

proposed rule does not contain such a 

mandate and the requirements of Title 

II of the Unfunded Mandates Reform 

Act of 1995 do not apply. 

Executive Order 13132, Federalism 

The FAA has analyzed this proposed 

rule under the principles and criteria of 

Executive Order 13132, Federalism. We 

determined that this action would not 

have a substantial direct effect on the 

States, on the relationship between the 

national Government and the States, or 

on the distribution of power and 

responsibilities among the various 

levels of government, and therefore 

would not have federalism implications. 

Regulations Affecting Intrastate 

Aviation in Alaska 

Section 1205 of the FAA 

Reauthorization Act of 1996 (110 Stat. 

3213) requires the Administrator, when 

modifying regulations in title 14 of the 

CFR in manner affecting intrastate 

aviation in Alaska, to consider the 

extent to which Alaska is not served by 

transportation modes other than 

aviation, and to establish such 

regulatory distinctions, as he or she 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70949 

considers appropriate. Because this 

proposed rule would apply to the 

certification of future designs of 

transport category airplanes and their 

subsequent operation, it could, if 

adopted, affect intrastate aviation in 

Alaska. The FAA therefore specifically 

requests comments on whether there is 

justification for applying the proposed 

rule differently in intrastate operations 

in Alaska. 

Plain English 

Executive Order 12866 (58 FR 51735, 

Oct. 4, 1993) requires each agency to 

write regulations that are simple and 

easy to understand. We invite your 

comments on how to make these 

proposed regulations easier to 

understand, including answers to 

questions such as the following: 

• Are the requirements in the 

proposed regulations clearly stated? 

• Do the proposed regulations contain 

unnecessary technical language or 

jargon that interferes with their clarity? 

• Would the regulations be easier to 

understand if they were divided into 

more (but shorter) sections? 

• Is the description in the preamble 

helpful in understanding the proposed 

regulations? 

Please send your comments to the 

address specified in the ADDRESSES

section. 

Environmental Analysis 

FAA Order 1050.1E identifies FAA 

actions that are categorically excluded 

from preparation of an environmental 

assessment or environmental impact 

statement under the National 

Environmental Policy Act in the 

absence of extraordinary circumstances. 

The FAA has determined this proposed 

rulemaking action qualifies for the 

categorical exclusion identified in 

paragraph 312f and involves no 

extraordinary circumstances. 

Regulations That Significantly Affect 

Energy Supply, Distribution, or Use 

We have determined that it is not a 

‘‘significant energy action’’ under the 

executive order. The FAA has analyzed 

this NPRM under Executive Order 

13211, Actions Concerning Regulations 

that Significantly Affect Energy Supply, 

Distribution, or Use (May 18, 2001). We 

have determined that it is not a 

‘‘significant energy action’’ under the 

executive order because the proposed 

rule is not likely to have a significant 

adverse effect on the supply, 

distribution, or use of energy. 

List of Subjects 

14 CFR Part 25 

Aircraft, Aviation safety, Reporting 

and recordkeeping requirements. 

14 CFR Part 91 

Aircraft, Aviation safety, Reporting 

and recordkeeping requirements. 

14 CFR Part 121 

Air carriers, Aircraft, Aviation safety, 

Reporting and recordkeeping 

requirements, Safety, Transportation. 

14 CFR Part 125 

Aircraft, Aviation safety, Reporting 

and recordkeeping requirements. 

14 CFR Part 129 

Air carriers, Aircraft, Aviation safety, 

Reporting and recordkeeping 

requirements, Security measures. 

V. The Proposed Amendment 

In consideration of the foregoing, the 

Federal Aviation Administration 

proposes to amend Chapter 1 of Title 14, 

Code of Federal Regulations (CFR) parts 

25, 91, 121, 125, and 129, as follows: 

PART 25—AIRWORTHINESS 

STANDARDS: TRANSPORT 

CATEGORY AIRPLANES 

1. The authority citation for part 25 

continues to read as follows: 

Authority: 49 U.S.C. 106(g), 40113, 44701, 

44702 and 44704. 

2. Amend § 25.1 by adding new 

paragraphs (c) and (d) to read as follows: 

§ 25.1 Applicability. 

* * * * * 

(c) This part also establishes 

requirements for holders of type 

certificates, supplemental type 

certificates, and field approvals to take 

specific actions necessary to support the 

continued airworthiness of transport 

category airplanes. 

(d) This part also establishes 

requirements for holders or licensees of 

type certificates for transport category 

airplanes to introduce design changes 

necessary for safety into newly 

produced airplanes. 

3. Amend § 25.2 by adding a new 

paragraph (d) to read as follows: 

§ 25.2 Special retroactive requirements. 

* * * * * 

(d) In addition to the requirements of 

this section, subpart I of this part 

contains requirements that apply to: 

(1) Holders of type certificates, and 

supplemental type certificates; 

(2) Applicants for type certificates, 

amendments to type certificates 

(including service bulletins describing 

design changes), and supplemental type 

certificates; 

(3) [Reserved]; 

(4) Licensees of type certificates. 

4. Amend § 25.981 by revising 

paragraphs (b) and (c) and adding 

paragraphs (d) and (e) to read as follows: 

§ 25.981 Fuel tank ignition prevention. 

* * * * * 

(b) Except as provided in paragraph 

(c) of this section, no fuel tank Fleet 

Average Flammability Exposure level on 

an airplane other than one designed 

solely for all-cargo operations may 

exceed three percent, or a fuel tank 

within the wing of the airplane model 

being evaluated. If the wing is not a 

conventional unheated aluminum wing, 

the analysis must be based on an 

assumed Equivalent Conventional 

Unheated Aluminum Wing. 

(1) Fleet Average Flammability 

Exposure is determined in accordance 

with Appendix L of this part. 

(2) Any fuel tank other than a main 

tank on an airplane other than one 

designed solely for all-cargo operations 

must meet the flammability exposure 

criteria of Appendix K to this part if any 

portion of the tank is located within the 

fuselage contour. 

(3) As used in this paragraph, 

(i) Equivalent Conventional Unheated 

Aluminum Wing is a semi-monocoque 

aluminum wing of a subsonic airplane 

that is equivalent in aerodynamic 

performance, structural capability, fuel 

tank capacity and tank configuration to 

the designed wing. 

(ii) Fleet Average Flammability 

Exposure is defined in Appendix L to 

this part and means the percentage of 

time the fuel tank ullage is flammable 

for a fleet of an airplane type operating 

over the range of flight lengths. 

(iii) Main Fuel Tank means a fuel tank 

that feeds fuel directly into one or more 

engines and holds required fuel reserves 

continually throughout each flight. 

(c) Paragraphs (b) and (e) of this 

section do not apply to a fuel tank if 

means are provided to mitigate the 

effects of an ignition of fuel vapors 

within that fuel tank such that no 

damage caused by an ignition will 

prevent continued safe flight and 

landing. 

(d) Critical design configuration 

control limitations (CDCCL), 

inspections, or other procedures must 

be established, as necessary, to prevent 

development of ignition sources within 

the fuel tank system pursuant to 

paragraph (a) of this section, to prevent 

increasing the flammability exposure of 

the tanks above that permitted under 

paragraph (b) of this section, and to 

prevent degradation of the performance 

70950 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

and reliability of any means provided 

according to paragraphs (a), (b) or (c). 

These CDCCL, inspections, and 

procedures must be included in the 

Airworthiness Limitations section of the 

instructions for continued airworthiness 

required by § 25.1529. Visible means of 

identifying critical features of the design 

must be placed in areas of the airplane 

where foreseeable maintenance actions, 

repairs, or alterations may compromise 

the critical design configuration 

limitations (e.g., color-coding of wire to 

identify separation limitation). These 

visible means must also be identified as 

CDCCL. 

(e) For airplanes designed solely for 

all-cargo operations, except as provided 

in paragraph (c) of this section, the fuel 

tank installation must include means to 

minimize the development of flammable 

vapors in the fuel tanks (in the context 

of this rule, ‘‘minimize’’ means to 

incorporate practicable design methods 

to reduce the likelihood of flammable 

vapors). 

5. Amend part 25 by adding a new 

subpart I to read as follows: 

Subpart I—Continued Airworthiness and 

Safety Improvements 

General 

Sec. 

25.1801 Purpose and Scope. 

25.1803 Definitions. 

25.1805–25.1813 [Reserved] 

Fuel Tank Flammability 

25.1815 Holders of type certificates: Fuel 

tank flammability safety. 

25.1817 Changes to type certificates 

affecting fuel tank flammability. 

25.1819 Pending type certification projects: 

Fuel tank flammability safety. 

25.1821 Newly produced airplanes: Fuel 

tank flammability safety. 

Subpart I—Continued Airworthiness 

and Safety Improvements 

General 

§ 25.1801 Purpose and scope. 

(a) This subpart establishes 

requirements for support of the 

continued airworthiness of and safety 

improvements for transport category 

airplanes. These requirements may 

include performing assessments, 

developing design changes, developing 

revisions to Instructions for Continued 

Airworthiness, and making necessary 

documentation available to affected 

persons. 

(b) This subpart applies to the 

following persons, as specified in each 

section of this subpart: 

(1) Holders of type certificates and 

supplemental type certificates. 

(2) Applicants for type certificates and 

changes to type certificates (including 

service bulletins describing design 

changes). Applicants for changes to type 

certificates must comply with the 

requirements of this subpart in addition 

to the airworthiness requirements 

determined applicable under § 21.101 of 

this subchapter. 

(3) [Reserved] 

(4) Holders of type certificates and 

their licensees producing new airplanes. 

§ 25.1803 Definitions. 

(a) Auxiliary Fuel Tank is a Normally 

Emptied fuel tank that has been 

installed pursuant to a supplemental 

type certificate or field approval to make 

additional fuel available. 

(b) Fleet Average Flammability 

Exposure has the meaning defined in 

Appendix L of this part. 

(c) FAA Oversight Office is the aircraft 

certification office or office of the 

Transport Airplane Directorate with 

oversight responsibility for the relevant 

type certificate, supplemental type 

certificate, or manufacturer, as 

determined by the Administrator. 

(d) Normally Emptied means a fuel 

tank other than a Main Fuel Tank as 

defined in 14 CFR 25.981(b). 

§ 25.1805–25.1813 [Reserved] 

Fuel Tank Flammability 

§ 25.1815 Holders of type certificates: Fuel 

tank flammability safety. 

(a) Applicability. Except as provided 

in paragraph (j) of this section, this 

section applies to transport category, 

turbine-powered airplanes with a type 

certificate issued after January 1, 1958, 

other than those designed solely for allcargo operations, that, as a result of 

original type certification or later 

increase in capacity have: 

(1) A maximum type-certificated 

passenger capacity of 30 or more, or 

(2) A maximum payload capacity of 

7,500 pounds or more. 

(b) Flammability Exposure Analysis—

(1) General. Within 150 days after 

[effective date of final rule], holders of 

type certificates must submit for 

approval to the FAA Oversight Office a 

flammability exposure analysis of all 

fuel tanks defined in the type design, as 

well as all design variations approved 

under the type certificate that affect 

flammability exposure. This analysis 

must be conducted in accordance with 

appendix L of this part. 

(2) Exception. This paragraph does 

not apply to fuel tanks for which the 

type certificate holder has notified the 

FAA under paragraph (g) of this section 

that it will provide design changes and 

service instructions for an Ignition 

Mitigation Means (IMM) meeting the 

requirements of paragraph (c)(2) of this 

section. 

(c) Design modifications. For fuel 

tanks with a Fleet Average Flammability 

Exposure level exceeding 7 percent, one 

of the following design modifications 

must be made. 

(1) Flammability Reduction Means 

(FRM). A means must be provided to 

reduce the fuel tank flammability. 

(i) Fuel tanks that are designed to be 

Normally Emptied must meet the 

flammability exposure criteria of 

Appendix K of this part if any portion 

of the tank is located within the fuselage 

contour. 

(ii) For all other fuel tanks, the FRM 

must meet all of the requirements of 

Appendix K of this part, except, instead 

of complying with paragraph K25.1, the 

Fleet Average Flammability Exposure 

level must not exceed 7 percent. 

(2) IMM. A means must be provided 

to mitigate the effects of an ignition of 

fuel vapors within the fuel tank such 

that no damage caused by an ignition 

will prevent continued safe flight and 

landing. 

(d) Design Changes and Service 

Instructions. No later than the 

applicable date stated in Table 1 of this 

section, holders of type certificates 

affected by this section must meet one 

of the following requirements: 

(1) FRM. The type certificate holder 

must submit for approval by the FAA 

Oversight Office design changes and 

service instructions for installation of 

fuel tank flammability reduction means 

(FRM) meeting the criteria of paragraph 

(c) of this section. 

(2) IMM. The type certificate holder 

must submit for approval by the FAA 

Oversight Office design changes and 

service instructions for installation of 

fuel tank IMM that comply with 14 CFR 

25.981(c) in effect on [effective date of 

final rule]. 

TABLE 1 

Model— Service instruction 

submittal date 

Boeing 

747 Series ............... December 31, 2005. 

737 Series ............... March 31, 2006. 

777 Series ............... March 31, 2006. 

767 Series ............... September 30, 2006. 

757 Series ............... March 31, 2007. 

707/720 Series ........ December 31, 2007. 

Airbus 

A319, A320, A321 

Series.

December 31, 2006. 

A300, A310 Series .. June 30, 2007. 

A330, A340 Series .. December 31, 2007. 

All other affected 

models.

Within 24 months of 

effective date of this 

amendment. 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70951 

(e) Instructions for Continued 

Airworthiness (ICA). For all fuel tanks, 

regardless of flammability exposure, no 

later than the applicable date specified 

in Table 1 of this section, holders of 

type certificates affected by this section 

must submit for approval by the FAA 

Oversight Office, critical design 

configuration control limitations 

(CDCCL), inspections, or other 

procedures to prevent increasing the 

flammability exposure of the tanks 

above that permitted under this section 

and to prevent degradation of the 

performance of any means provided 

under paragraph (c)(1) or (c)(2) of this 

section. These CDCCL, inspections, and 

procedures must be included in the 

Airworthiness Limitations section of the 

ICA required by 14 CFR 25.1529 or 

paragraph (f) of this section. Visible 

means to identify critical features of the 

design must be placed in areas of the 

airplane where foreseeable maintenance 

actions, repairs, or alterations may 

compromise the critical design 

configuration limitations. These visible 

means must also be identified as a 

CDCCL. 

(f) Airworthiness Limitations. Unless 

previously accomplished, no later than 

the applicable date specified in Table 1 

of this section, holders of type 

certificates affected by this section must 

establish an Airworthiness Limitations 

Section (ALS) of the maintenance 

manual or ICA for each airplane 

configuration evaluated under 

paragraph (b)(1) and submit it to the 

FAA oversight office for approval. The 

ALS must include a section that 

contains the (CDCCL), inspections, or 

other procedures developed under 

paragraph (e) of this section. 

(g) Compliance Plan for Flammability 

Exposure Analysis. Within 60 days after 

[effective date of final rule], each holder 

of a type certificate identified in 

paragraph (a) of this section must 

submit to the FAA Oversight Office a 

compliance plan consisting of the 

following: 

(1) A proposed project schedule for 

submitting the required analysis, or a 

determination that compliance with 

paragraph (b) of this section is not 

required as design changes and service 

instructions for IMM will be made 

available. 

(2) A proposed means of compliance 

with paragraph (b) of this section, if 

applicable. 

(3) If the affected holder proposes a 

means of compliance that differs from 

that described in FAA advisory 

material, a detailed explanation of how 

the proposed means will comply with 

this section. 

(h) Compliance Plan for Design 

Changes and Service Instructions. 

Within 210 days after [effective date of 

final rule], each holder of a type 

certificate required to comply with 

paragraph (d) of this section must 

submit to the FAA Oversight Office a 

compliance plan consisting of the 

following: 

(1) A proposed project schedule, 

identifying all major milestones, for 

meeting the compliance dates specified 

in paragraph (d) of this section. 

(2) A proposed means of compliance 

with paragraph (d) of this section. 

(3) If the affected holder proposes a 

means of compliance that differs from 

that described in FAA advisory 

material, a detailed explanation of how 

the proposed means will comply with 

this section. 

(4) A proposal for submitting a draft 

of all compliance items required by 

paragraph (d) of this section for review 

by the FAA Oversight Office not less 

than 60 days before the compliance time 

specified in paragraph (d) of this 

section. 

(5) A proposal for how the approved 

service information and any necessary 

modification parts will be made 

available to affected persons. 

(i) Deficiencies in Compliance Plans. 

Each affected type certificate holder 

must implement the compliance plans 

as approved under paragraph (g) and (h) 

of this section. The FAA Oversight 

Office will notify the affected holder of 

deficiencies in the proposed compliance 

plan, or in the type certificate holder’s 

implementation of the plan, and provide 

the means for correcting those 

deficiencies. The type certificate holder 

must submit a corrected plan to the 

FAA Oversight Office within 30 days 

after such notification and implement 

the corrected plan. 

(j) Exceptions. The requirements of 

this section do not apply to the 

following airplane models: 

(1) Convair CV–240, 340, 440, 

including turbine powered conversions. 

(2) Lockheed L–188. 

(3) Vickers Armstrong Viscount. 

(4) Douglas DC–3, including turbine 

powered conversions. 

(5) Bombardier CL–44. 

(6) Mitsubishi YS–11. 

(7) BAC 1–11. 

(8) Concorde. 

(9) deHavilland D.H. 106 Comet 4C. 

(10) VFW-Vereinigte Flugtechnische 

VFW–614. 

(11) Illyushin Aviation IL 96T. 

(12) Bristol Aircraft Britannia 305. 

(13) Handley Page Handley Page 

Herald Type 300. 

(14) Avions Marcel Dassault—Breguet 

Aviation Mercure 100C. 

(15) Airbus Caravelle. 

(16) Fokker F27. 

(17) Maryland Air Service V–27/FH–

227. 

§ 25.1817 Changes to type certificates 

affecting fuel tank flammability. 

(a) Applicability. This section applies 

to the following design changes to any 

airplane subject to 14 CFR 25.1815(a) 

unless the design change converts the 

airplane to one designed solely for allcargo operations: 

(1) Any fuel tank designed to be 

Normally Emptied if any of the 

following occurred before [effective date 

of final rule]: 

(i) The fuel tank was installed on an 

airplane pursuant to a supplemental 

type certificate or a field approval; 

(ii) An application for a supplemental 

type certificate or an amendment to a 

type certificate was made, or 

(iii) A field approval was granted. 

(2) Installation of a fuel tank designed 

to be Normally Emptied, including 

Auxiliary Fuel Tanks, changes to 

existing fuel tank capacity, and changes 

that may increase the flammability 

exposure of an existing fuel tank on 

airplanes for which an application for a 

supplemental type certificate or an 

amendment to a type certificate is made 

on or after [effective date of final rule]. 

(b) Flammability Exposure Analysis—

(1) General. By the times specified in 

paragraphs (b)(1)(i) and (b)(1)(ii) of this 

section, each person subject to this 

section must submit for approval to the 

FAA Oversight Office a flammability 

exposure analysis of the Auxiliary Fuel 

Tanks or other affected fuel tanks, as 

defined in the type design. This analysis 

must be conducted in accordance with 

appendix L of this part. 

(i) Holders of supplemental type 

certificates and field approvals: Within 

12 months of [effective date of final 

rule], 

(ii) Applicants for supplemental type 

certificates and for amendments to type 

certificates: Within 12 months of 

[effective date of final rule], or before 

the certificate is issued, whichever 

occurs later. 

(2) Exception. This paragraph does 

not apply to fuel tanks for which the 

type certificate holder, supplemental 

type certificate holder, and field 

approval holder has notified the FAA 

under paragraph (f) of this section that 

it will provide design changes and 

service instructions for an IMM meeting 

the requirements of § 25.981(c) of this 

part in effect on [effective date of final 

rule]. 

(c) Impact Assessment. By the times 

specified in paragraphs (c)(1) and (c)(2) 

of this section, each person subject to 

70952 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

this section must submit for approval to 

the FAA Oversight Office an assessment 

of the fuel tank system, as modified by 

their design change. The assessment 

must identify any features of the design 

change that compromise any critical 

design configuration control limitation 

(CDCCL) applicable to any airplane on 

which the design change is eligible for 

installation. 

(1) Holders of supplemental type 

certificates and field approvals: Within 

6 months of the date of FAA approval 

of the submission identified in 

§ 25.1815(d) for the applicable airplane 

model. 

(2) Applicants for supplemental type 

certificates and for amendments to type 

certificates: Within 6 months of the date 

of FAA approval of the submission 

identified in 14 CFR 25.1815(d) for the 

applicable airplane model or before the 

certificate is issued, whichever occurs 

later. 

(d) Design Changes and Service 

Instructions. By the times specified in 

paragraph (e) of this section, each 

person subject to this section must meet 

the requirements of paragraphs (d)(1), 

(d)(2), (d)(3), and (d)(4) of this section, 

as applicable. 

(1) If the application was submitted 

before June 6, 2001, for any fuel tank 

exceeding a Fleet Average Flammability 

Exposure level of 7 percent, submit for 

approval by the FAA oversight office 

design changes and service instructions 

for installation of either: 

(i) IMM. Fuel tank IMM that comply 

with 14 CFR 25.981(c) of this part in 

effect on [effective date of final rule]; or 

(ii) FRM. Any fuel tank that is 

designed to be Normally Emptied, 

including Auxiliary Fuel tanks, must 

meet the flammability exposure criteria 

of Appendix K if any portion of the tank 

is located within the fuselage contour. 

For all other fuel tanks, the FRM must 

meet all of the requirements of 

Appendix K of this part, except, instead 

of complying with paragraph K25.1, the 

Fleet Average Flammability Exposure 

level must not exceed 7 percent. 

(2) If the application was made on or 

after June 6, 2001, comply with the 

requirements of 14 CFR 25.981, in effect 

on [effective date of final rule], for all 

fuel tanks subject to this section. 

(3) For design changes adding a fuel 

tank designed to be Normally Emptied, 

including Auxiliary Fuel Tanks, or 

changing fuel tank capacity, establish 

critical design configuration control 

limitations (CDCCL), inspections, or 

other procedures to prevent increasing 

the flammability exposure of the tanks 

above that permitted under this section 

and to prevent degradation of the 

performance of any means provided 

according to paragraphs (d)(1)(i) or 

(d)(1)(ii) of this section. These CDCCL, 

inspections, and procedures must be 

included in the Airworthiness 

Limitations section of the ICA required 

by 14 CFR 25.1529 of this part. Visible 

means to identify critical features of the 

design must be placed in areas of the 

airplane where foreseeable maintenance 

actions, repairs, or alterations may 

compromise the critical design 

configuration limitations. These visible 

means must also be identified as 

CDCCL. 

(4) If the assessment required by 

paragraph (c) of this section identifies 

any features of the design change that 

compromise any CDCCL applicable to 

any airplane on which the design 

change is eligible for installation, the 

holder or applicant must submit for 

approval by the FAA Oversight Office 

design changes and service instructions 

for Flammability Impact Mitigation 

Means (FIMM) that would bring the 

design change into compliance with the 

CDCCL. Any fuel tank modified as 

required by this paragraph must also be 

evaluated as required by paragraph (b) 

of this section and comply with 

paragraphs (d)(1), (d)(2), and (d)(3) of 

this section, as applicable. 

(e) Compliance Times for Design 

Changes and Service Instructions. The 

following persons subject to this section 

must comply with the requirements of 

paragraph (d) of this section at the 

specified times. 

(1) Holders of supplemental type 

certificates and field approvals: Within 

24 months of the date identified in 14 

CFR 25.1815(d) for the applicable 

airplane model. 

(2) Applicants for supplemental type 

certificates and for amendments to type 

certificates: Within 24 months of the 

date identified in 14 CFR 25.1815(d) for 

the applicable airplane model or before 

the certificate is issued, whichever 

occurs later. 

(f) Compliance Planning. By the 

applicable times specified in Table 2 of 

this section, each person subject to this 

section must submit for approval by the 

FAA Oversight Office compliance plans 

for the flammability exposure analysis 

required by paragraph (b) of this section, 

the impact assessment required by 

paragraph (c) of this section, and the 

design changes and service instructions 

required by paragraph (d) of this 

section. Each person’s compliance plans 

must include the following: 

(1) A proposed project schedule for 

submitting the required analysis or 

impact assessment. 

(2) A proposed means of compliance 

with paragraph (d) of this section. 

(3) If the affected holder proposes a 

means of compliance that differs from 

that described in FAA advisory 

material, a detailed explanation of how 

the proposed means will be shown to 

comply with this section. 

(4) For the requirements of paragraph 

(d) of this section, a proposal for 

submitting a draft of all design changes, 

if any are required, and CDCCLs for 

review by the FAA Oversight Office not 

less than 60 days before the compliance 

time specified in paragraph (e) of this 

section. 

(5) For the requirements of paragraph 

(d) of this section, a proposal for how 

the approved service information and 

any necessary modification parts will be 

made available to affected persons. 

TABLE 2.—COMPLIANCE PLANNING DATES

Flammability exposure analysis 

plan Impact assessment plan Design changes and service instructions plan 

STC and Field Approval Holders ... 60 days after [effective date of 

final rule].

60 days after the date identified in 

§ 25.1815(d) for the applicable 

airplane model.

240 days after the date identified 

in § 25.1815(d) for the applicable airplane model. 

STC and ATC Applicants ............... 60 days after [effective date of 

final rule] or before the certificate is issued, whichever occurs later.

60 days after the date identified in 

§ 25.1815(d) for the applicable 

airplane model or before the 

certificate is issued, whichever 

occurs later.

240 days after the date identified 

in § 25.1815(d) for the applicable airplane model or before the 

certificate is issued, whichever 

occurs later. 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70953 

(g) Deficiencies in Compliance Plans. 

Each person subject to this section must 

implement the compliance plans as 

approved under paragraph (f) of this 

section. The FAA Oversight Office will 

notify the affected person of deficiencies 

in the proposed compliance plan, or in 

the person’s implementation of the plan, 

and of the means for correcting those 

deficiencies. The person must submit a 

corrected plan to the FAA oversight 

office within 30 days after such 

notification, and implement the 

corrected plan. 

§ 25.1819 Pending type certification 

projects: Fuel tank flammability safety. 

(a) Applicability. This section applies 

to any new type certificate for a 

transport category airplane, other than 

one designed solely for all-cargo 

operations, if the application was made 

before [effective date of final rule and if 

the certificate was not issued before 

[effective date of final rule]. This section 

applies only if the airplane would 

have—

(1) A maximum type-certificated 

passenger capacity of 30 or more, or 

(2) A maximum payload capacity of 

7,500 pounds or more. 

(b) Flammability Exposure Analysis. 

Before issuance of the type certificate, 

the applicant must submit for approval 

to the FAA Oversight Office a 

flammability exposure analysis of all 

fuel tanks defined in the type design. 

This analysis must be conducted in 

accordance with Appendix L of this 

part. 

(c) If the application was made before 

June 6, 2001, the requirements of 

paragraphs (c)(1) and (c)(2) of this 

section apply. 

(1) Any fuel tank meeting all of the 

criteria stated in paragraphs (c)(1)(i), 

(c)(1)(ii) and (c)(1)(iii) of this section 

must have FRM or IMM that meet the 

requirements of 14 CFR 25.981 of this 

part in effect on [effective date of final 

rule]. 

(i) The fuel tank is a fuel tank 

designed to be Normally Emptied. 

(ii) Any portion of the fuel tank is 

located within the fuselage contour. 

(iii) The fuel tank exceeds a Fleet 

Average Flammability Exposure level of 

this part, of 7 percent. 

(2) All other fuel tanks that exceed a 

Fleet Average Flammability Exposure 

level of 7 percent must have either an 

IMM meeting 14 CFR 25.981(c) of this 

part in effect on [effective date of final 

rule] or an FRM meeting the 

requirements of Appendix K of this part, 

except, instead of complying with 

paragraph K25.1, the Fleet Average 

Flammability Exposure level must not 

exceed 7 percent. 

(d) If the application was made on or 

after June 6, 2001, the requirements of 

14 CFR 25.981 in effect on [effective 

date of final rule] apply. 

(e) Any design change to a type 

certificate subject to this section that 

adds an Auxiliary Fuel Tank or fuel 

tank designed to be Normally Emptied, 

that increases fuel tank capacity, or that 

may increase the flammability exposure 

of an existing fuel tank, must meet the 

requirements of 14 CFR 25.981 in effect 

on [effective date of final rule]. 

(f) For all fuel tanks, regardless of 

flammability exposure, no later than the 

applicable date specified in Table 1 of 

this subpart, holders of type certificates 

affected by this section must submit for 

approval by the FAA Oversight Office, 

critical design configuration control 

limitations (CDCCL), inspections, or 

other procedures to prevent increasing 

the flammability exposure of the tanks 

above that permitted under paragraph 

(c) or (d) of this section and to prevent 

degradation of the performance of any 

means provided under paragraph (c) or 

(d) of this section. These CDCCL, 

inspections, and procedures must be 

included in the Airworthiness 

Limitations section of the ICA required 

by 14 CFR 25.1529. Visible means to 

identify critical features of the design 

must be placed in areas of the airplane 

where foreseeable maintenance actions, 

repairs, or alterations may compromise 

the critical design configuration 

limitations. These visible means must 

also be identified as CDCCL. 

§ 25.1821 Newly produced airplanes: Fuel 

tank flammability safety. 

(a) Applicability: This section applies 

to holders of type certificates for 

airplanes, other than those designed or 

produced solely for all-cargo operations, 

subject to 14 CFR 25.1815(c) of this part 

when application is made for original 

certificates of airworthiness or export 

airworthiness approvals after the 

applicable dates shown in 14 CFR 

25.1815(d) of this part. This section only 

applies if the FAA has jurisdiction over 

the organization responsible for final 

assembly of the airplane. 

(b) Any fuel tank meeting all of the 

criteria stated in paragraphs (b)(1), (b)(2) 

and (b)(3) of this section must have 

flammability reduction means (FRM) or 

ignition mitigation means (IMM) that 

meet the requirements of 14 CFR 25.981 

in effect on [effective date of final rule]. 

(1) The fuel tank is Normally 

Emptied. 

(2) Any portion of the fuel tank is 

located within the fuselage contour. 

(3) The fuel tank exceeds a Fleet 

Average Flammability Exposure level of 

7 percent. 

(c) All other fuel tanks that exceed an 

Fleet Average Flammability Exposure 

level of 7 percent must have an IMM 

that meets 14 CFR 25.981(c) in effect on 

[effective date of final rule] or an FRM 

that meets all of the requirements of 

Appendix K to this part, except instead 

of complying with paragraph K25.1, the 

Fleet Average Flammability Exposure 

level must not exceed 7 percent. 

6. Part 25 is amended by adding a 

new appendix K to read as follows: 

Appendix K to Part 25—Fuel Tank System 

Flammability Reduction Means 

K25.1 Fuel tank flammability exposure 

requirements 

(a) The Fleet Average Flammability 

Exposure level of each fuel tank, as 

determined in accordance with Appendix L 

of this part, must not exceed 3 percent of the 

Flammability Exposure Evaluation Time 

(FEET), as defined in Appendix L of this part. 

If flammability reduction means (FRM) are 

used, neither time periods when any FRM is 

operational but the fuel tank is not inert, nor 

time periods when any FRM is inoperative 

may contribute more than 1.8 percent to the 

3 percent average fleet flammability exposure 

of a tank. 

(b) The Fleet Average Flammability 

Exposure, as defined in Appendix L of this 

part, of each fuel tank for ground, takeoff and 

climb phases of flight during warm days 

must not exceed 3 percent of FEET in each 

of these phases. The analysis must consider 

the following conditions. 

(1) The analysis must use the subset of 

flights starting with a sea level ground 

ambient temperature of 80°F (standard day 

plus 21°F atmosphere) or more, from the 

flammability exposure analysis done for 

overall performance. 

(2) For the ground, takeoff, and climb 

phases of flight, the average flammability 

exposure must be calculated by dividing the 

time during the specific flight phase the fuel 

tank is flammable by the total time of the 

specific flight phase. 

(3) Compliance with this paragraph may be 

shown using only those flights for which the 

airplane is dispatched with the flammability 

reduction means operational. 

K25.2 Showing compliance 

(a) The applicant must provide data from 

analysis, ground testing, and flight testing, or 

any combination of these, that: 

(1) Validate the parameters used in the 

analysis required by paragraph K25.1; 

(2) Substantiate that the FRM is effective at 

limiting flammability exposure in all 

compartments of each tank for which the 

FRM is used to show compliance with 

paragraph K25.1; and 

(3) Describe the circumstances under 

which the FRM would not be operated 

during each phase of flight. 

(b) The applicant must validate that the 

FRM meets the requirements of paragraph 

K25.1 with any combination of engine model, 

engine thrust rating, fuel type, and relevant 

pneumatic system configuration for which 

approval is sought. 

70954 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

K25.3 Reliability indications and 

maintenance access 

(a) Reliability indications must be provided 

to identify latent failures of the FRM. 

(b) Sufficient accessibility to FRM 

reliability indications must be provided for 

maintenance personnel or the flightcrew. 

(c) The access doors and panels to the fuel 

tanks with FRMs (including any tanks that 

communicate with a tank via a vent system), 

and to any other confined spaces or enclosed 

areas that could contain hazardous 

atmosphere under normal conditions or 

failure conditions must be permanently 

stenciled, marked, or placarded to warn 

maintenance personnel of the possible 

presence of a potentially hazardous 

atmosphere. 

K25.4 Airworthiness limitations and 

procedures 

(a) If FRM is used to comply with 

paragraph K25.1, Airworthiness Limitations 

must be identified for all maintenance or 

inspection tasks required to identify failures 

of components within the FRM that are 

needed to meet paragraph K25.1. 

(b) Maintenance procedures must be 

developed to identify any hazards to be 

considered during maintenance of the FRM. 

These procedures must be included in the 

instructions for continued airworthiness 

(ICA). 

K25.5 Reliability reporting 

The effects of airplane component failures 

on FRM reliability must be assessed on an 

on-going basis. The applicant must do the 

following: 

(a) Demonstrate effective means to ensure 

collection of FRM reliability data. The means 

must provide data affecting FRM reliability, 

such as component failures. 

(b) Provide a report to the FAA on a 

quarterly basis for the first five years after 

service introduction. After that period, 

continued quarterly reporting may be 

replaced with other reliability tracking 

methods found acceptable to the FAA or 

eliminated if it is established that the 

reliability of the FRM meets, and will 

continue to meet, the exposure requirements 

of paragraph K25.1. 

(c) Develop service instructions or revise 

the applicable airplane manual, according to 

a schedule approved by the FAA Oversight 

Office, as defined in Subpart I of this part, 

to correct any failures of the FRM that occur 

in service that could increase any fuel tank’s 

Fleet Average Flammability Exposure to 

more than that required by paragraph K25.1. 

7. Part 25 is amended by adding a 

new appendix L to read as follows: 

Appendix L to Part 25—Fuel Tank 

Flammability Exposure and Reliability 

Analysis 

L25.1 General 

(a) This appendix specifies the 

requirements for conducting fuel tank fleet 

average flammability exposure analyses 

required to meet § 25.981(b) and Appendix K 

of this part. This appendix defines 

parameters affecting fuel tank flammability 

that must be used in performing the analysis. 

These include parameters that affect all 

airplanes within the fleet, such as a statistical 

distribution of ambient temperature, fuel 

flash point, flight lengths, and airplane 

descent rate. Demonstration of compliance 

also requires application of factors specific to 

the airplane model being evaluated. Factors 

that need to be included are maximum range, 

cruise mach number, typical altitude where 

the airplane begins initial cruise phase of 

flight fuel temperature during both ground 

and flight times, and the performance of a 

flammability reduction means (FRM) if 

installed. 

(b) The FAA program defined in FAA 

document, Fuel Tank Flammability 

Assessment Method Users Manual, must be 

used as the means of compliance with 

§ 25.981(b) and appendix K. [You must 

proceed in accordance with FAA document, 

Fuel Tank Flammability Assessment Method 

Users Manual. The Director of the Federal 

Register approves this incorporation by 

reference in accordance with 5 U.S.C. 552(a) 

and 1 CFR part 51. You may obtain a copy 

from the following Web site: http:// 

www.fire.tc.faa.gov/systems/fueltank/ 

FTFAM.stm_. You may inspect a copy at the 

Transport Airplane Directorate, Aircraft 

Certification Service, 1601 Lind Avenue, 

SW., Renton, Washington 98055–4056 or at 

the Office of the Federal Register, 800 North 

Capitol Street, NW., Suite 700, Washington, 

DC. The following definitions, input 

variables, and data tables must be used in the 

program to determine fleet average 

flammability exposure for a specific airplane 

model. 

L25.2 Definitions 

(a) Bulk Average Fuel Temperature means 

the average fuel temperature within the fuel 

tank or different sections of the tank if the 

tank is subdivided by baffles or 

compartments. 

(b) Flammability Exposure Evaluation 

Time (FEET). The time from the start of 

preparing the airplane for flight, through the 

flight and landing, until all payload is 

unloaded, and all passengers and crew have 

disembarked. In the Monte Carlo program, 

the flight time is randomly selected from the 

Flight Length Distribution (Table 3), the preflight times are provided as a function of the 

flight time, and the post-flight time is a 

constant 30 minutes. 

(c) Flammable. With respect to a fluid or 

gas, flammable means susceptible to igniting 

readily or to exploding (14 CFR Part 1, 

Definitions). A non-flammable ullage is one 

where the fuel-air vapor is too lean or too 

rich to burn or is inert as defined below. For 

the purposes of this appendix, a fuel tank 

that is not inert is considered flammable 

when the bulk average fuel temperature 

within the tank is within the flammable 

range for the fuel type being used. For any 

fuel tank that is subdivided into sections by 

baffles or compartments, the tank is 

considered flammable when the bulk average 

fuel temperature within any section of the 

tank, that is not inert, is within the 

flammable range for the fuel type being used. 

(d) Flash Point. The flash point of a 

flammable fluid means the lowest 

temperature at which the application of a 

flame to a heated sample causes the vapor to 

ignite momentarily, or ‘‘flash.’’ Table 1 of this 

appendix provides the flash point for the 

standard fuel to be used in the analysis. 

(e) Fleet average flammability exposure is 

the percentage of the flammability exposure 

evaluation time (FEET) the fuel tank ullage 

is flammable for a fleet of an airplane type 

operating over the range of flight lengths in 

a world-wide range of environmental 

conditions and fuel properties as defined in 

this appendix. 

(f) Gaussian Distribution is another name 

for the normal distribution, a symmetrical 

frequency distribution having a precise 

mathematical formula relating the mean and 

standard deviation of the samples. Gaussian 

distributions yield bell shaped frequency 

curves having a preponderance of values 

around the mean with progressively fewer 

observations as the curve extends outward. 

(g) Hazardous atmosphere. An atmosphere 

that may expose maintenance personnel, 

passengers or flight crew to the risk of death, 

incapacitation, impairment of ability to selfrescue (that is, escape unaided from a 

confined space), injury, or acute illness. 

(h) Inert. For the purpose of this appendix, 

the tank is considered inert when the bulk 

average oxygen concentration within each 

compartment of the tank is 12 percent or less 

from sea level up to 10,000 feet altitude, then 

linearly increasing from 12 percent at 10,000 

feet to 14.5 percent at 40,000 feet altitude, 

and extrapolated linearly above that altitude. 

(i) Inerting. A process where a 

noncombustible gas is introduced into the 

ullage of a fuel tank so that the ullage 

becomes non-flammable. 

(j) Monte Carlo Analysis. The analytical 

method that is specified in this appendix as 

the compliance means for assessing the fleet 

average flammability exposure time for a fuel 

tank. 

(k) Standard deviation is a statistical 

measure of the dispersion or variation in a 

distribution, equal to the square root of the 

arithmetic mean of the squares of the 

deviations from the arithmetic means. 

(l) Transport Effects. For purposes of this 

appendix, transport effects are the change in 

fuel vapor concentration in a fuel tank 

caused by low fuel conditions and fuel 

condensation and vaporization. 

(m) Ullage. The volume within the fuel 

tank not occupied by liquid fuel. 

L25.3 Fuel tank flammability exposure 

analysis 

(a) A flammability exposure analysis must 

be conducted for the fuel tank under 

evaluation to determine fleet average 

flammability exposure for the airplane and 

fuel types under evaluation. For fuel tanks 

that are subdivided by baffles or 

compartments, an analysis must be 

performed either for each section of the tank, 

or for the section of the tank having the 

highest flammability exposure. Consideration 

of transport effects is not allowed in the 

analysis. The Monte Carlo program is 

contained in FAA document, Fuel Tank 

Flammability Assessment Method Users 

Manual. The parameters specified in sections 

L25.3(b) and (c) must be used in the fuel tank 

flammability exposure ‘‘Monte Carlo’’

analysis. 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70955 

(b) The following parameters are defined in 

the Monte Carlo analysis and provided in 

paragraph L25.4: 

(1) Cruise Ambient Temperature—as 

defined in this appendix. 

(2) Ground Temperature—as defined in 

this appendix. 

(3) Fuel Flash Point—as defined in this 

appendix. 

(4) Flight Length Distribution—that must 

be used is defined in Table 2 of this 

appendix. 

(5) Airplane Climb and Descent Profiles—

the applicant must use the climb and descent 

profiles defined in the users manual. 

(c) Parameters that are specific to the 

particular airplane model under evaluation 

that must be provided as inputs to the Monte 

Carlo analysis are: 

(1) Airplane Cruise Altitude. 

(2) Fuel Tank Quantities. If fuel quantity 

affects fuel tank flammability, inputs to the 

Monte Carlo analysis must be provided that 

represent the actual fuel quantity within the 

fuel tank or compartment of the fuel tank 

throughout each of the flights being 

evaluated. Input values for this data must be 

obtained from ground and flight test data or 

the approved FAA fuel management 

procedures. 

(3) Airplane Cruise Mach Number. 

(4) Airplane Maximum Range. 

(5) Fuel Tank Thermal Characteristics. If 

fuel temperature affects fuel tank 

flammability, inputs to the Monte Carlo 

analysis must be provided that represent the 

actual bulk average fuel temperature within 

the fuel tank throughout each of the flights 

being evaluated. For fuel tanks that are 

subdivided by baffles or compartments, bulk 

average fuel temperature inputs must be 

provided either for each section of the tank 

or for the section of the tank having the 

highest flammability exposure. Input values 

for these data must be obtained from ground 

and flight test data or a thermal model of the 

tank that has been validated by ground and 

flight test data. 

(6) Maximum airplane operating 

temperature limit as defined by any 

limitations in the airplane flight manual. 

(d) Fuel Tank FRM Model. If FRM is used, 

an FAA approved Monte Carlo program must 

be used to show compliance with the 

flammability requirements of § 25.981 and 

Appendix K of this part. The program must 

determine the time periods during each flight 

phase when the fuel tank or compartment 

with the FRM would be flammable. The 

following factors must be considered in 

establishing these time periods: 

(1) Any time periods throughout the 

flammability exposure evaluation time and 

under the full range of expected operating 

conditions, when the FRM is operating 

properly but fails to maintain a nonflammable fuel tank because of the effects of 

the fuel tank vent system or other causes, 

(2) If dispatch with the system inoperative 

under the Master Minimum Equipment List 

(MMEL) is requested, the time period 

assumed in the reliability analysis, (60 flight 

hours must be used for a 10-day MMEL 

dispatch limit unless an alternative period 

has been approved by the Administrator), 

(3) Frequency and duration of time periods 

of FRM inoperability, substantiated by test or 

analysis acceptable to the FAA, caused by 

latent or known failures, including airplane 

system shut-downs and failures that could 

cause the FRM to shut down or become 

inoperative, 

(4) Effects of failures of the FRM that could 

increase the flammability exposure of the 

fuel tank, 

(5) Oxygen Evolution: If an FRM is used 

that is affected by oxygen concentrations in 

the fuel tank, the time periods when oxygen 

evolution from the fuel results in the fuel 

tank or compartment exceeding the inert 

level. The applicant must include any times 

when oxygen evolution from the fuel in the 

tank or compartment under evaluation would 

result in a flammable fuel tank. The oxygen 

evolution rate that must be used is defined 

in the user’s manual. 

(6) If an inerting system FRM is used, the 

effects of any air that may enter the fuel tank 

following the last flight of the day due to 

changes in ambient temperature, as defined 

in Table 4, during a 12-hour overnight 

period. 

(e) The applicant must submit to the FAA 

oversight office for approval the fuel tank 

flammability analysis, including the airplanespecific parameters identified under 

paragraph L25.3(c) of this appendix and any 

deviations from the parameters identified in 

paragraph L25.3(b), that affect flammability 

exposure, substantiating data, and any 

airworthiness limitations and other 

conditions assumed in the analysis, must be 

submitted. 

L25.4 Variables and data tables 

The following data must be used when 

conducting a flammability exposure analysis 

to determine the fleet average flammability 

exposure. Variables used to calculate fleet 

flammability exposure must include 

atmospheric ambient temperatures, flight 

length, flammability exposure evaluation 

time, fuel flash point, thermal characteristics 

of the fuel tank, overnight temperature drop, 

and oxygen evolution from the fuel into the 

ullage. 

(a) Atmospheric Ambient Temperatures 

and Fuel Properties. 

(1) In order to predict flammability 

exposure during a given flight, the variation 

of ground ambient temperatures, cruise 

ambient temperatures, and a method to 

compute the transition from ground to cruise 

and back again must be used. The variation 

of the ground and cruise ambient 

temperatures and the flash point of the fuel 

is defined by a Gaussian curve, given by the 

50 percent value and a ± 1-standard deviation 

value. 

(2) Ambient Temperature: Under the 

program, the ground and cruise ambient 

temperatures are linked by a set of 

assumptions on the atmosphere. The 

temperature varies with altitude following 

the International Standard Atmosphere (ISA) 

rate of change from the ground ambient 

temperature until the cruise temperature for 

the flight is reached. Above this altitude, the 

ambient temperature is fixed at the cruise 

ambient temperature. This results in a 

variation in the upper atmospheric 

temperature. For cold days, an inversion is 

applied up to 10,000 feet, and then the ISA 

rate of change is used. 

(3) Fuel properties: 

(A) For Jet A fuel, the variation of flash 

point of the fuel is defined by a Gaussian 

curve, given by the 50 percent value and a 

± 1-standard deviation, as shown in Table 1. 

(B) The flammability envelope of the fuel 

that must be used for the flammability 

exposure analysis is a function of the flash 

point of the fuel selected by the Monte Carlo 

for a given flight. The flammability envelope 

for the fuel is defined by the upper 

flammability limit (UFL) and lower 

flammability limit (LFL) as follows: 

(i) LFL at sea level = flash point 

temperature of the fuel at sea level minus 10 

°F. LFL decreases from sea level value with 

increasing altitude at a rate of 1 °F per 808 

feet. 

(ii) UFL at sea level = flash point 

temperature of the fuel at sea level plus 63.5 

°F. UFL decreases from the sea level value 

with increasing altitude at a rate of 1 °F per 

512 feet. 

(4) For each flight analyzed, a separate 

random number must be generated for each 

of the three parameters (ground ambient 

temperature, cruise ambient temperature, and 

fuel flash point) using the Gaussian 

distribution defined in Table 1. 

TABLE 1.—GAUSSIAN DISTRIBUTION FOR GROUND AMBIENT TEMPERATURE, CRUISE AMBIENT TEMPERATURE, AND FUEL

FLASH POINT

Parameter 

Temperature in deg F 

Ground ambient 

temperature 

Cruise ambient 

temperature 

Fuel flash point 

(FP) 

Mean Temp ...................................................................................................................... 59.95 ¥70 120 

Neg 1 std dev .................................................................................................................. 20.14 8 8 

Pos 1 std dev ................................................................................................................... 17.28 8 8 

70956 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

(b) The Flight Length Distribution defined 

in Table 2 must be used in the Monte Carlo 

analysis. 

TABLE 2.—FLIGHT LENGTH DISTRIBUTION

Flight length (NM) Airplane maximum range—nautical miles (NM) 

From To 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 

Distribution of flight lengths (percentage of total) 

0 ............ 200 ........ 11.7 7.5 6.2 5.5 4.7 4.0 3.4 3.0 2.6 2.3 

200 ........ 400 ........ 27.3 19.9 17.0 15.2 13.2 11.4 9.7 8.5 7.5 6.7 

400 ........ 600 ........ 46.3 40.0 35.7 32.6 28.5 24.9 21.2 18.7 16.4 14.8 

600 ........ 800 ........ 10.3 11.6 11.0 10.2 9.1 8.0 6.9 6.1 5.4 4.8 

800 ........ 1000 ...... 4.4 8.5 8.6 8.2 7.4 6.6 5.7 5.0 4.5 4.0 

1000 ...... 1200 ...... 0.0 4.8 5.3 5.3 4.8 4.3 3.8 3.3 3.0 2.7 

1200 ...... 1400 ...... 0.0 3.6 4.4 4.5 4.2 3.8 3.3 3.0 2.7 2.4 

1400 ...... 1600 ...... 0.0 2.2 3.3 3.5 3.3 3.1 2.7 2.4 2.2 2.0 

1600 ...... 1800 ...... 0.0 1.2 2.3 2.6 2.5 2.4 2.1 1.9 1.7 1.6 

1800 ...... 2000 ...... 0.0 0.7 2.2 2.6 2.6 2.5 2.2 2.0 1.8 1.7 

2000 ...... 2200 ...... 0.0 0.0 1.6 2.1 2.2 2.1 1.9 1.7 1.6 1.4 

2200 ...... 2400 ...... 0.0 0.0 1.1 1.6 1.7 1.7 1.6 1.4 1.3 1.2 

2400 ...... 2600 ...... 0.0 0.0 0.7 1.2 1.4 1.4 1.3 1.2 1.1 1.0 

2600 ...... 2800 ...... 0.0 0.0 0.4 0.9 1.0 1.1 1.0 0.9 0.9 0.8 

2800 ...... 3000 ...... 0.0 0.0 0.2 0.6 0.7 0.8 0.7 0.7 0.6 0.6 

3000 ...... 3200 ...... 0.0 0.0 0.0 0.6 0.8 0.8 0.8 0.8 0.7 0.7 

3200 ...... 3400 ...... 0.0 0.0 0.0 0.7 1.1 1.2 1.2 1.1 1.1 1.0 

3400 ...... 3600 ...... 0.0 0.0 0.0 0.7 1.3 1.6 1.6 1.5 1.5 1.4 

3600 ...... 3800 ...... 0.0 0.0 0.0 0.9 2.2 2.7 2.8 2.7 2.6 2.5 

3800 ...... 4000 ...... 0.0 0.0 0.0 0.5 2.0 2.6 2.8 2.8 2.7 2.6 

4000 ...... 4200 ...... 0.0 0.0 0.0 0.0 2.1 3.0 3.2 3.3 3.2 3.1 

4200 ...... 4400 ...... 0.0 0.0 0.0 0.0 1.4 2.2 2.5 2.6 2.6 2.5 

4400 ...... 4600 ...... 0.0 0.0 0.0 0.0 1.0 2.0 2.3 2.5 2.5 2.4 

4600 ...... 4800 ...... 0.0 0.0 0.0 0.0 0.6 1.5 1.8 2.0 2.0 2.0 

4800 ...... 5000 ...... 0.0 0.0 0.0 0.0 0.2 1.0 1.4 1.5 1.6 1.5 

5000 ...... 5200 ...... 0.0 0.0 0.0 0.0 0.0 0.8 1.1 1.3 1.3 1.3 

5200 ...... 5400 ...... 0.0 0.0 0.0 0.0 0.0 0.8 1.2 1.5 1.6 1.6 

5400 ...... 5600 ...... 0.0 0.0 0.0 0.0 0.0 0.9 1.7 2.1 2.2 2.3 

5600 ...... 5800 ...... 0.0 0.0 0.0 0.0 0.0 0.6 1.6 2.2 2.4 2.5 

5800 ...... 6000 ...... 0.0 0.0 0.0 0.0 0.0 0.2 1.8 2.4 2.8 2.9 

6000 ...... 6200 ...... 0.0 0.0 0.0 0.0 0.0 0.0 1.7 2.6 3.1 3.3 

6200 ...... 6400 ...... 0.0 0.0 0.0 0.0 0.0 0.0 1.4 2.4 2.9 3.1 

6400 ...... 6600 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.9 1.8 2.2 2.5 

6600 ...... 6800 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.5 1.2 1.6 1.9 

6800 ...... 7000 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.8 1.1 1.3 

7000 ...... 7200 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4 0.7 0.8 

7200 ...... 7400 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.5 0.7 

7400 ...... 7600 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.5 0.6 

7600 ...... 7800 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.5 0.7 

7800 ...... 8000 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.6 0.8 

8000 ...... 8200 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.8 

8200 ...... 8400 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 1.0 

8400 ...... 8600 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 1.3 

8600 ...... 8800 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4 1.1 

8800 ...... 9000 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.8 

9000 ...... 9200 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 

9200 ...... 9400 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 

9400 ...... 9600 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 

9600 ...... 9800 ...... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 

9800 ...... 10000 .... 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 

(c) Overnight Temperature Drop. For 

airplanes on which FRM is installed, the 

overnight temperature drop for this appendix 

is defined using: 

(1) A temperature at the beginning of the 

overnight period that equals the landing 

temperature of the previous flight that is a 

random value based on a Gaussian 

distribution; and 

(2) An overnight temperature drop that is 

a random value based on a Gaussian 

distribution. 

(3) For any flight that will end with an 

overnight ground period (one flight per day 

out of an average of number of flights per 

day, depending on utilization of the 

particular airplane model being evaluated), 

the landing outside air temperature (OAT) is 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70957 

to be chosen as a random value from the 

following Gaussian curve: 

TABLE 3.—LANDING OUTSIDE AIR

TEMPERATURE

Parameter 

Landing outside 

air temperature 

°F 

Mean Temperature ....... 58.68 

negative 1 std dev ........ 20.55 

positive 1 std dev ......... 13.21 

(4) The outside ambient air temperature 

(OAT) overnight temperature drop is to be 

chosen as a random value from the following 

Gaussian curve: 

TABLE 4.—OUTSIDE AIR

TEMPERATURE (OAT) DROP

Parameter OAT drop 

temperature °F 

Mean Temp .................. 12.0 

1 std dev ....................... 6.0 

(d) Number of Simulated Flights Required 

in Analysis. In order for the Monte Carlo 

analysis to be valid for showing compliance 

with the fleet average and warm day 

flammability exposure requirements, the 

applicant must run the analysis for a 

minimum number of flights to ensure that the 

fleet average and warm day flammability 

exposure for the fuel tank under evaluation 

meets the applicable flammability limits 

defined in Table 5. 

TABLE 5.—FLAMMABILITY EXPOSURE LIMIT

Minimum number of flights in Monte Carlo analysis 

Maximum acceptable Monte Carlo 

average fuel tank 

flammability exposure (%) to meet 

3% requirements 

Maximum acceptable Monte Carlo 

average fuel tank 

flammability exposure (%) to meet 

7% requirements 

10,000 ...................................................................................................................................................... 2.91 6.79 

100,000 .................................................................................................................................................... 2.98 6.96 

1,000,000 ................................................................................................................................................. 3.00 7.00 

PART 91—GENERAL OPERATING AND 

FLIGHT RULES 

8. The authority citation for part 91 

continues to read as follows: 

Authority: 49 U.S.C. 1155, 40103, 40113, 

40120, 44101, 44111, 44701, 44709, 44711, 

44715, 44716, 11417, 44722, 46306, 36315, 

46316, 46504, 46506–46507, 47122, 47508, 

47528–47531, articles 12 and 20 of the 

Convention on International Civil Aviation 

(61 stat. 1180). 

9. Amend § 91.1 by adding a new 

paragraph (d) to read as follows: 

§ 91.1 Applicability. 

* * * * * 

(d) This part also establishes 

requirements for operators to take 

actions to support the continued 

airworthiness of each airplane. 

10. Amend part 91 by adding a new 

subpart L to read as follows: 

Subpart L—Continued Airworthiness and 

Safety Improvements 

Sec. 

91.1501 Purpose and definition. 

91.1503–91.1507 [Reserved] 

91.1509 Flammability reduction means. 

Subpart L—Continued Airworthiness 

and Safety Improvements 

§ 91.1501 Purpose and definition. 

(a) This subpart establishes 

requirements for operators to take 

actions necessary to support the 

continued airworthiness of each 

airplane. Such actions may include, but 

are not limited to, revising the 

inspection program, incorporating 

design changes, and incorporating 

revisions to Instructions for Continued 

Airworthiness (ICA). 

(b) For purposes of this subpart, the 

‘‘FAA Oversight Office’’ is the aircraft 

certification office or office of the 

Transport Airplane Directorate with 

oversight responsibility for the relevant 

type certificate or supplemental type 

certificate, as determined by the 

Administrator. 

§§ 91.1503–91.1507 [Reserved] 

§ 91.1509 Flammability reduction means. 

(a) Applicability. This section applies 

to persons operating transport category, 

turbine-powered airplanes for which 

development of an ignition mitigation 

means (IMM), flammability reduction 

means (FRM), or Flammability Impact 

Mitigation Means (FIMM) is required 

under §§ 25.1815, 25.1817, or 25.1819 of 

this chapter. 

(b) New Production Airplanes. Except 

in accordance with § 91.213 of this part, 

no person may operate an airplane on 

which IMM or FRM has been installed 

by the type certificate holder or licensee 

under 14 CFR 25.1821 unless the IMM 

or FRM is operational. 

(c) Auxiliary Fuel Tanks. After the 

applicable date stated in paragraphs 

(e)(1) and (e)(2), no person may operate 

any airplane subject to this section that 

has an Auxiliary fuel tank installed 

pursuant to a field approval, unless the 

following requirements are met: 

(1) The person complies with 14 CFR 

25.1817 by the applicable date stated in 

that section. 

(2) The person installs IMM, FRM, or 

FIMM, as applicable, that is approved 

by the FAA Oversight Office. 

(3) Except in accordance with 

§ 91.213 of this part, the IMM, FRM, or 

FIMM, as applicable, are operational. 

(d) Retrofit. After the dates specified 

in paragraph (e) of this section, no 

person may operate an airplane to 

which this section applies unless the 

requirements of paragraphs (d)(1) and 

(d)(2) of this section are met. 

(1) IMM, FRM, and FIMM, if required 

by §§ 25.1815, 25.1817, or 25.1819 of 

this chapter, that are approved by the 

FAA Oversight Office, are installed in at 

least the percentage of the operator’s 

fleet of each airplane model indicated in 

the applicable column of Table 1 of this 

section. 

(2) Except in accordance with 

§ 91.213 of this part, the IMM, FRM, and 

FIMM, as applicable, are operational. 

(e) Compliance Times. The 

installations required by paragraph (d) 

of this section must be accomplished no 

later than the applicable dates specified 

in paragraph (e)(1) or (e)(2) of this 

section. 

(1) The applicable dates specified in 

Table 1. 

70958 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

TABLE 1 

Model Compliance date for 50% of fleet Compliance date for 100% of 

fleet 

Boeing 

747 Series .................................................................... December 31, 2009 .................................................... December 31, 2012. 

737 Series .................................................................... March 31, 2010 ........................................................... March 31, 2013. 

777 Series .................................................................... March 31, 2010 ........................................................... March 31, 2013. 

767 Series .................................................................... September 30, 2010 ................................................... September 30, 2013. 

757 Series .................................................................... March 31, 2011 ........................................................... March 31, 2014. 

707/720 Series ............................................................. December 31, 2011 .................................................... December 31, 2014. 

Airbus 

A319, A320, A321 Series ............................................ December 31, 2010 .................................................... December 31, 2013. 

A300, A310 Series ....................................................... June 30, 2011 ............................................................. June 30, 2014. 

A330, A340 Series ....................................................... December 31, 2011 .................................................... December 31, 2014. 

All other affected models ............................................. Within 4 years after the effective date of this amendment.Within 7 years after the effective 

date of this amendment. 

(2) For those persons that have only 

one airplane of a model identified in 

Table 1, the compliance date is that 

stated for 100% of Fleet in Table 1 of 

this section. 

(f) Early Compliance. 

Notwithstanding paragraphs (c) and (d) 

of this section, no person may operate 

an airplane on which IMM, FRM or 

FIMM has been installed unless the 

IMM, FRM or FIMM is operational, 

except in accordance with § 91.213 of 

this part. 

(g) Inspection Program Revisions. No 

person may operate an airplane to 

which this section applies after the date 

specified in paragraph (g)(1) or (g)(2) of 

this section, as applicable, unless the 

inspection program for that airplane is 

revised to include applicable 

airworthiness limitations that are 

approved by the FAA Oversight Office 

under §§ 25.1815, 25.1817 or 25.1819 of 

this chapter. 

(1) For any airplane that must be 

modified in accordance with paragraph 

(d) of this section, the date of return to 

service after those modifications are 

accomplished. 

(2) For any airplane that is not 

required to be modified in accordance 

with paragraph (d) of this section, the 

date one year after the date of approval 

of the airworthiness limitations by the 

FAA Oversight Office. 

(h) After the inspection program is 

revised as required by paragraph (g) of 

this section, before returning an airplane 

to service after any alteration for which 

airworthiness limitations are required 

by §§ 25.1817, or 25.1819 of this 

chapter, the person must revise the 

inspection program for the airplane to 

include those airworthiness limitations. 

(i) The inspection program changes 

identified in paragraphs (g) and (h) of 

this section must be submitted to the 

operator’s Principal Inspector or the 

Flight Standards District Office (FSDO) 

responsible for review and approval 

prior to incorporation. 

§ 91.410 [Redesignated as § 91.1505] 

11. Redesignate § 91.410 as new 

§ 91.1505. 

§ 91.410 [Added and Reserved] 

12. A new § 91.410 is added and 

reserved. 

PART 121—OPERATING 

REQUIREMENTS: DOMESTIC, FLAG, 

AND SUPPLEMENTAL OPERATIONS 

13. The authority citation for part 121 

continues to read as follows: 

Authority: 49 U.S.C. 106(g), 40113, 40119, 

41706, 44101, 44701–44702, 44705, 44709–

44711, 44713, 44716–44717, 44722, 44901, 

44903–44904, 44012, 46105, 46105, 46301. 

14. Amend § 121.1 by adding a new 

paragraph (g) to read as follows: 

§ 121.1 Applicability. 

* * * * * 

(g) This part also establishes 

requirements for operators to take 

actions to support the continued 

airworthiness of each airplane. 

15. Amend part 121 by adding a new 

Subpart AA to read as follows: 

Subpart AA—Continued Airworthiness and 

Safety Improvements 

Sec. 

121.1101 Purpose and definition. 

121.1103–121.1115 [Reserved] 

121.1117 Flammability reduction means. 

Subpart AA—Continued Airworthiness 

and Safety Improvements 

§ 121.1101 Purpose and definition. 

(a) This subpart requires persons 

holding an air carrier or operating 

certificate under part 119 of this chapter 

to support the continued airworthiness 

of each airplane. These requirements 

may include, but are not limited to, 

revising the maintenance program, 

incorporating design changes, and 

incorporating revisions to Instructions 

for Continued Airworthiness. 

(b) For purposes of this subpart, the 

‘‘FAA Oversight Office’’ is the aircraft 

certification office or office of the 

Transport Airplane Directorate with 

oversight responsibility for the relevant 

type certificate or supplemental type 

certificate, as determined by the 

Administrator. 

§ 121.1103–121.1115 [Reserved] 

§ 121.1117 Flammability reduction means. 

(a) Applicability. This section applies 

to certificate holders operating transport 

category, turbine-powered airplanes for 

which development of an ignition 

mitigation means (IMM), flammability 

reduction means (FRM), or 

Flammability Impact Mitigation Means 

(FIMM) is required under §§ 25.1815, 

25.1817, or 25.1819 of this chapter. 

(b) New Production Airplanes. Except 

in accordance with § 121.628 of this 

part, no person may operate an airplane 

on which IMM or FRM has been 

installed by the type certificate holder 

or licensee under 14 CFR 25.1821 unless 

the IMM or FRM is operational. 

(c) Auxiliary Fuel Tanks. After the 

applicable date stated in paragraphs 

(e)(1) and (e)(2) of this section, no 

certificate holder may operate any 

airplane subject to this section that has 

an Auxiliary Fuel Tank installed 

pursuant to a field approval, unless the 

following requirements are met: 

(1) The certificate holder complies 

with 14 CFR 25.1817 by the applicable 

date stated in that section. 

(2) The certificate holder installs 

IMM, FRM or FIMM, as applicable, that 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70959 

is approved by the FAA Oversight 

Office. 

(3) Except in accordance with 

§ 121.628 of this part, the IMM, FRM or 

FIMM, as applicable, are operational. 

(d) Retrofit. After the dates specified 

in paragraph (e) of this section, no 

certificate holder may operate an 

airplane to which this section applies 

unless the requirements of paragraphs 

(d)(1) and (d)(2) of this section are met. 

(1) IMM, FRM or FIMM, if required by 

§§ 25.1815, 25.1817, or 25.1819 of this 

chapter, that are approved by the FAA 

Oversight Office, are installed in at least 

the percentage of the operator’s fleet of 

each airplane model indicated in the 

applicable column of Table 1 of this 

section. 

(2) Except in accordance with 

§ 121.628 of this part, the IMM, FRM or 

FIMM, as applicable, are operational. 

(e) Compliance Times. The 

installations required by paragraph (d) 

of this section must be accomplished no 

later than the applicable dates specified 

in paragraph (e)(1) or (e)(2) of this 

section. 

(1) The applicable dates specified in 

Table 1. 

TABLE 1 

Model Compliance date for 50% of fleet Compliance date for 100% of 

fleet 

Boeing 

747 Series .................................................................... December 31, 2009 .................................................... December 31, 2012. 

737 Series .................................................................... March 31, 2010 ........................................................... March 31, 2013. 

777 Series .................................................................... March 31, 2010 ........................................................... March 31, 2013. 

767 Series .................................................................... September 30, 2010 ................................................... September 30, 2013. 

757 Series .................................................................... March 31, 2011 ........................................................... March 31, 2014. 

707/720 Series ............................................................. December 31, 2011 .................................................... December 31, 2014. 

Airbus 

A319, A320, A321 Series ............................................ December 31, 2010 .................................................... December 31, 2013. 

A300, A310 Series ....................................................... June 30, 2011 ............................................................. June 30, 2014. 

A330, A340 Series ....................................................... December 31, 2011 .................................................... December 31, 2014. 

All other affected models ............................................. Within 4 years after the effective date of this amendment.Within 7 years after the effective 

date of this amendment. 

(2) For those certificate holders that 

have only one airplane of a model 

identified in Table 1, the compliance 

date is that stated for 100 percent of 

Fleet in Table 1 of this section. 

(f) Early Compliance. 

Notwithstanding paragraphs (c) and (d) 

of this section, no person may operate 

an airplane on which IMM or FRM has 

been installed unless the IMM or FRM 

is operational, except in accordance 

with § 121.628 of this part. 

(g) Maintenance Program Revisions. 

No certificate holder may operate an 

airplane to which this section applies 

after the date specified in paragraph 

(g)(1) or (g)(2) of this section, as 

applicable, unless the maintenance 

program for that airplane is revised to 

include applicable airworthiness 

limitations that are approved by the 

FAA Oversight Office under §§ 25.1815, 

25.1817 or 25.1819 of this chapter. 

(1) For any airplane that must be 

modified in accordance with paragraph 

(d) of this section, the date of return to 

service after those modifications are 

accomplished. 

(2) For any airplane that is not 

required to be modified in accordance 

with paragraph (d) of this section, the 

date one year after the date approval of 

the airworthiness limitations by the 

FAA Oversight Office. 

(h) After the maintenance program is 

revised as required by paragraph (g) of 

this section, before returning an airplane 

to service after any alteration for which 

airworthiness limitations are required 

by §§ 25.1817, or 25.1819 of this 

chapter, the certificate holder must 

revise the maintenance program for the 

airplane to include those airworthiness 

limitations. 

(i) The maintenance program changes 

identified in paragraphs (g) and (h) of 

this section must be submitted to the 

operator’s Principal Inspector 

responsible for review and approval 

prior to incorporation 

§ 121.368 [Redesignated as § 121.1105] 

16. Redesignate 121.368 as new 

§ 121.1105. 

§ 121.368 [Added and Reserved] 

17. A new § 121.368 is added and 

reserved. 

§ 121.370 [Redesignated as § 121.1107] 

18. Redesignate § 121.370 as new 

§ 121.1107. 

§ 121.370 [Added and Reserved] 

19. A new § 121.370 is added and 

reserved. 

§ 121.370a [Redesignated as § 121.1109] 

20–21. Redesignate § 121.370a as new 

§ 121.1109. 

§ 121.370a [Added and Reserved] 

PART 125—CERTIFICATION AND 

OPERATIONS; AIRPLANES HAVING A 

SEATING CAPCITY OF 20 OR MORE 

PASSENGERS OR A MAXIMUM 

PAYLOAD CAPACITY OF 6,000 

POUNDS OR MORE; AND RULES 

GOVERNING PERSONS ON BOARD 

SUCH AIRCRAFT 

22. The authority citation for part 125 

continues to read as follows: 

Authority: 49 U.S.C. 106(g), 40113, 44701–

44702, 44705, 44710–44711, 44713, 44716–

44717, 44722 

23. Amend § 125.1 by adding a new 

paragraph (e) to read as follows: 

§ 125.1 Applicability. 

* * * * * 

(e) This part also establishes 

requirements for operators to take 

actions to support the continued 

airworthiness of each airplane. 

24. Amend part 125 by adding a new 

subpart M to read as follows: 

Subpart M—Continued Airworthiness and 

Safety Improvements 

Sec. 

125.501 Purpose and definition. 

125.503–125.507 [Reserved] 

125.509 Flammability reduction means. 

70960 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

Subpart M—Continued Airworthiness 

and Safety Improvements 

§ 125.501 Purpose and definition. 

(a) This subpart establishes 

requirements for operators to take 

actions necessary to report the 

continued airworthiness of each 

airplane. Such actions may include, but 

are not limited to, revising the 

inspection program, incorporating 

design changes, and incorporating 

revisions to Instructions for Continued 

Airworthiness. 

(b) For purposes of this subpart, the 

‘‘FAA Oversight Office’’ is the aircraft 

certification office or office of the 

Transport Airplane Directorate with 

oversight responsibility for the relevant 

type certification or supplemental type 

certificate, as determined by the 

Administrator. 

§§ 125.503–125.507 [Reserved] 

§ 125.509 Flammability reduction means. 

(a) Applicability. This section applies 

to certificate holders operating transport 

category, turbine-powered airplanes for 

which development of an ignition 

mitigation means (IMM), flammability 

reduction means (FRM), or 

Flammability Impact Mitigation Means 

(FIMM) is required under §§ 25.1815, 

25.1817, or 25.1819 of this chapter. 

(b) New Production Airplanes. Except 

in accordance with § 125.201 of this 

part, no person may operate an airplane 

on which IMM or FRM has been 

installed by the type certificate holder 

or licensee under 14 CFR 25.1821 unless 

the IMM or FRM is operational. 

(c) Auxiliary Fuel Tanks. After the 

applicable date stated in paragraphs 

(e)(1) and (e)(2) of this section, no 

certificate holder may operate any 

airplane subject to this section that has 

an Auxiliary Fuel Tank installed 

pursuant to a field approval, unless the 

following requirements are met—

(1) The certificate holder complies 

with 14 CFR 25.1817 by the applicable 

date stated in that section. 

(2) The certificate holder installs 

IMM, FRM or FIMM, as applicable, that 

is approved by the FAA Oversight 

Office. 

(3) Except in accordance with 

§ 125.201 of this part, the IMM, FRM or 

FIMM, as applicable, are operational. 

(d) Retrofit. After the dates specified 

in paragraph (e) of this section, no 

certificate holder may operate an 

airplane to which this section applies 

unless the requirements of paragraphs 

(d)(1) and (d)(2) of this section are met. 

(1) IMM, FRM or FIMM, if required by 

§§ 25.1815, 25.1817, or 25.1819 of this 

chapter, that are approved by the FAA 

Oversight Office, are installed in at least 

the percentage of the operator’s fleet of 

each airplane model indicated in the 

applicable column of Table 1 of this 

section. 

(2) Except in accordance with 

§ 125.201 of this part, the IMM, FRM or 

FIMM, as applicable, are operational. 

(e) Compliance Times. The 

installations required by paragraph (d) 

of this section must be accomplished no 

later than the applicable dates specified 

in paragraph (e)(1) or (e)(2) of this 

section. 

(1) The applicable dates specified in 

Table 1. 

TABLE 1 

Model Compliance date for 50% of fleet Compliance date for 100% of 

fleet 

Boeing 

747 Series .................................................................... December 31, 2009 .................................................... December 31, 2012. 

737 Series .................................................................... March 31, 2010 ........................................................... March 31, 2013. 

777 Series .................................................................... March 31, 2010 ........................................................... March 31, 2013. 

767 Series .................................................................... September 30, 2010 ................................................... September 30, 2013. 

757 Series .................................................................... March 31, 2011 ........................................................... March 31, 2014. 

707/720 Series ............................................................. December 31, 2011 .................................................... December 31, 2014. 

Airbus 

A319, A320, A321 Series ............................................ December 31, 2010 .................................................... December 31, 2013. 

A300, A310 Series ....................................................... June 30, 2011 ............................................................. June 30, 2014. 

A330, A340 Series ....................................................... December 31, 2011 .................................................... December 31, 2014. 

All other affected models ............................................. Within 4 years after the effective date of this amendment.Within 7 years after the effective 

date of this amendment. 

(2) For those certificate holders that 

have only one airplane of a model 

identified in Table 1, the compliance 

date is that stated for 100 percent of 

Fleet in Table 1 of this section. 

(f) Early Compliance. 

Notwithstanding paragraphs (c) and (d) 

of this section, no person may operate 

an airplane on which IMM or FRM has 

been installed unless the IMM or FRM 

is operational, except in accordance 

with § 125.201 of this part. 

(g) Maintenance Program Revisions. 

No certificate holder may operate an 

airplane to which this section applies 

after the date specified in paragraph 

(g)(1) or (g)(2) of this section, as 

applicable, unless the maintenance 

program for that airplane is revised to 

include applicable airworthiness 

limitations that are approved by the 

FAA Oversight Office under §§ 25.1815, 

25.1817 or 25.1819 of this chapter. 

(1) For any airplane that must be 

modified in accordance with paragraph 

(d) of this section, the date of return to 

service after those modifications are 

accomplished. 

(2) For any airplane that is not 

required to be modified in accordance 

with paragraph (d) of this section, the 

date one year after the date approval of 

the airworthiness limitations by the 

FAA Oversight Office. 

(h) After the maintenance program is 

revised as required by paragraph (g) of 

this section, before returning an airplane 

to service after any alteration for which 

airworthiness limitations are required 

by §§ 25.1817, or 25.1819 of this 

chapter, the certificate holder must 

revise the maintenance program for the 

airplane to include those airworthiness 

limitations. 

(i) The maintenance program changes 

identified in paragraphs (g) and (h) of 

this section must be submitted to the 

operator’s Principal Inspector 

responsible for review and approval 

prior to incorporation. 

§ 125.248 [Redesignated as § 125.505] 

25. Redesignate § 125.248 as new 

§ 125.505. 

Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 70961 

§ 125.248 [Added and Reserved] 

26. A new § 125.248 is added and 

reserved. 

PART 129—OPERATIONS: FOREIGN 

AIR CARRIERS AND FOREIGN 

OPERATORS OF U.S.-REGISTERED 

AIRCRAFT ENGAGED IN COMMON 

CARRIAGE 

27. The authority citation for part 129 

continues to read as follows: 

Authority: 49 U.S.C. 1372, 49113, 440119, 

44101, 44701–44702, 447–5, 44709–44711, 

44713, 44716–44717, 44722, 44901–44904, 

44906, 44912, 44105, 107–71 sec. 104. 

28. Amend § 129.1 by revising 

paragraph (b), and adding a new 

paragraph (d) to read as follows: 

§ 129.1 Applicability and definition. 

* * * * * 

(b) Operations of U.S.-registered 

aircraft solely outside the United States. 

In addition to the operations specified 

under paragraph (a) of this section, 

§§ 129.14 and 129.20 and subpart B of 

this part also apply to U.S.-registered 

aircraft operated solely outside the 

United States in common carriage by a 

foreign person or foreign air carrier. 

* * * * * 

(d) This part also establishes 

requirements for an operator to take 

actions to support the continued 

airworthiness of each airplane. 29. Amend part 129 by adding subpart 

A and designating § 129.1 through 

§ 129.15 and § 129.17 through § 129.29 

into subpart A to read as follows: 

Subpart A—General 

Sec. 

129.1 Applicability and definitions. 

129.11 Operations specifications. 

129.13 Airworthiness and registration 

certificates. 

129.14 Maintenance program and minimum 

equipment list requirements for U.S. 

registered aircraft. 

129.15 Flight crewmember certificates. 

129.17 Radio equipment. 

129.18 Collision avoidance system. 

129.19 Air traffic rules and procedures. 

129.20 Digital flight data recorders. 

129.21 Control of traffic. 

129.23 Transport category cargo service 

airplanes: Increased zero fuel and 

landing weights. 

129.25 Airplane security. 

129.28 Flightdeck security. 

129.29 Smoking prohibitions. 

30. Amend part 129 by adding subpart 

B to read as follows: 

Subpart B—Continued Airworthiness and 

Safety Improvements 

Sec. 

129.101 Purpose and definition. 

129.103–129.115 [Reserved] 

129.117 Flammability reduction means. 

Subpart B—Continued Airworthiness 

and Safety Improvements 

§ 129.101 Purpose and definition. 

(a) This subpart requires a foreign 

person or foreign air carrier operating a 

U.S.-registered airplane in common 

carriage to support the continued 

airworthiness of each airplane. These 

requirements may include, but are not 

limited to, revising the maintenance 

program, incorporating design changes, 

and incorporating revisions to 

Instructions for Continued 

Airworthiness. 

(b) For purposes of this subpart, the 

‘‘FAA Oversight Office’’ is the aircraft 

certification office or office of the 

Transport Airplane Directorate with 

oversight responsibility for the relevant 

type certificate or supplemental type 

certificate, as determined by the 

Administrator. 

§ § 129.103–129.115 [Reserved] 

§ 129.117 Flammability reduction means. 

(a) Applicability. This section applies 

to foreign persons and foreign air 

carriers operating transport category, 

turbine-powered airplanes for which 

development of an ignition mitigation 

means (IMM), flammability reduction 

means (FRM), or Flammability Impact 

Mitigation Means (FIMM) is required 

under §§ 25.1815, 25.1817, or 25.1819 of 

this chapter. (b) New Production Airplanes. Except 

in accordance with § 129.14 of this part, 

no foreign person or foreign air carrier 

may operate an airplane on which IMM 

or FRM has been installed by the type 

certificate holder or licensee under 14 

CFR 25.1821 unless the IMM or FRM is 

operational. 

(c) Auxiliary Fuel Tanks. After the 

applicable date stated in paragraphs 

(e)(1) and (e)(2), no foreign person or 

foreign air carrier may operate any 

airplane subject to this section that has 

an Auxiliary Fuel Tank installed 

pursuant to a field approval, unless the 

following requirements are met: 

(1) The foreign person or foreign air 

carrier complies with 14 CFR 25.1817 

by the applicable date stated in that 

section. 

(2) The foreign person or foreign air 

carrier installs IMM, FRM or FIMM, as 

applicable, that are approved by the 

FAA Oversight Office. 

(3) Except in accordance with 

§ 129.14 of this part, the IMM, FRM or 

FIMM, as applicable, are operational. 

(d) Retrofit. After the dates specified 

in paragraph (e) of this section, no 

foreign person or foreign air carrier may 

operate an airplane to which this 

section applies unless the requirements 

of paragraphs (d)(1) and (d)(2) of this 

section are met. 

(1) IMM, FRM or FIMM, if required by 

§§ 25.1815, 25.1817, or 25.1819 of this 

chapter, that are approved by the FAA 

Oversight Office, are installed in at least 

the percentage of the operator’s fleet of 

each airplane model indicated in the 

applicable column of Table 1 of this 

section. 

(2) Except in accordance with 

§ 129.14 of this part, the IMM, FRM or 

FIMM, as applicable, are operational. 

(e) Compliance Times. The 

installations required by paragraph (d) 

of this section must be accomplished no 

later than the applicable dates specified 

in paragraph (e)(1) or (e)(2) of this 

section. 

(1) The applicable dates specified in 

Table 1. 

TABLE 1 

Model Compliance date for 50% of fleet Compliance date for 100% of 

fleet 

Boeing 

747 Series .................................................................... December 31, 2009 .................................................... December 31, 2012. 

737 Series .................................................................... March 31, 2010 ........................................................... March 31, 2013. 

777 Series .................................................................... March 31, 2010 ........................................................... March 31, 2013. 

767 Series .................................................................... September 30, 2010 ................................................... September 30, 2013. 

757 Series .................................................................... March 31, 2011 ........................................................... March 31, 2014. 

707/720 Series ............................................................. December 31, 2011 .................................................... December 31, 2014. 

Airbus 

A319, A320, A321 Series ............................................ December 31, 2010 .................................................... December 31, 2013. 

70962 Federal Register / Vol. 70, No. 225 / Wednesday, November 23, 2005 / Proposed Rules 

TABLE 1—Continued 

Model Compliance date for 50% of fleet Compliance date for 100% of 

fleet 

A300, A310 Series ....................................................... June 30, 2011 ............................................................. June 30, 2014. 

A330, A340 Series ....................................................... December 31, 2011 .................................................... December 31, 2014. 

All other affected models ............................................. Within 4 years after the effective date of this amendment.Within 7 years after the effective 

date of this amendment. 

(2) For those foreign persons or 

foreign air carriers that have only one 

airplane of a model identified in Table 

1, the compliance date is that stated for 

100 percent of Fleet in Table 1 of this 

section. 

(f) Early Compliance. 

Notwithstanding paragraphs (c) and (d) 

of this section, no person may operate 

an airplane on which IMM or FRM has 

been installed unless the IMM or FRM 

is operational, except in accordance 

with § 129.14 of this part. 

(g) Maintenance Program Revisions. 

No foreign person or foreign air carrier 

may operate an airplane to which this 

section applies after the date specified 

in paragraph (g)(1) or (g)(2) of this 

section, as applicable, unless the 

maintenance program for that airplane 

is revised to include applicable 

airworthiness limitations that are 

approved by the FAA Oversight Office 

under §§ 25.1815, 25.1817 or 25.1819 of 

this chapter. 

(1) For any airplane that must be 

modified in accordance with paragraph 

(d) of this section, the date of return to 

service after those modifications are 

accomplished. 

(2) For any airplane that is not 

required to be modified in accordance 

with paragraph (d) of this section, the 

date one year after the date approval of 

the airworthiness limitations by the 

FAA Oversight Office. 

(h) After the maintenance program is 

revised as required by paragraph (g) of 

this section, before returning an airplane 

to service after any alteration for which 

airworthiness limitations are required 

by §§ 25.1817, or 25.1819 of this 

chapter, the foreign person or foreign air 

carrier must revise the maintenance 

program for the airplane to include 

those airworthiness limitations. 

(i) The maintenance program changes 

identified in paragraphs (g) and (h) of 

this section must be submitted to the 

operator’s Principal Inspector for review 

and approval prior to incorporation. 

§ 129.16 [Redesignated as § 129.109] 

31. Redesignate § 129.16 as new 

§ 129.109. 

§ 129.16 [Added and Reserved] 

32. A new § 129.16 is added and 

reserved. 

§ 129.32 [Redesignated as § 129.107] 

33. Redesignate § 129.32 as new 

§ 129.107. 

§ 129.32 [Added and Reserved] 

34. A new § 129.32 is added and 

reserved. 

§ 129.33 [Redesignated as § 129.105] 

35. Redesignate § 129.33 as new 

§ 129.105. 

§ 129.33 [Added and Reserved] 

36. A new § 129.33 is added and 

reserved. 

Issued in Washington, DC, on November 

17, 2005. 

Dorenda D. Baker, 

Acting Director, Aircraft Certification Service. 

[FR Doc. 05–23109 Filed 11–17–05; 4:06 pm] 

BILLING CODE 4910–13–P