[Federal Register Volume 70, Number 225 (Wednesday, November 23, 2005)]
[Proposed Rules]
[Pages 70922-70962]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-23109]



[[Page 70921]]

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Part II





Department of Transportation





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Federal Aviation Administration



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14 CFR Parts 25, 91, et al.



Reduction of Fuel Tank Flammability in Transport Category Airplanes; 
Proposed Rule

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

[[Page 70922]]


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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).

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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 
cost-effective 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: <a href="/cdn-cgi/l/email-protection#1a7773717f347e75696e7f686e5a7c7b7b347d756c"><span class="__cf_email__" data-cfemail="cea3a7a5abe0aaa1bdbaabbcba8ea8afafe0a9a1b8">[email protected]</span></a>.

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

[[Page 70923]]

    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 Bogot[aacute], 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 Bogot[aacute] 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 [deg]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.
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    \1\ None 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.
    \2\ Philippine Airlines 737 accident in 1990 and the Thai 
Airlines accident in 2001.
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    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

[[Page 70924]]

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 type-
certification 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 ignition-source 
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).
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    \3\ The 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.
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    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 Sec.  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

[[Page 70925]]

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 piston-powered 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 [deg]F. The 
vapor will ignite, however, once the fuel temperature reaches 
approximately 175 [deg]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 
[deg]F.\4\ Use of Jet A or Jet A-1 fuel thus tends to limit the risk of 
high flammability to warmer days.
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    \4\ Most transport category airplanes used in air carrier 
service are approved for operation at altitudes from sea level to 
45,000 feet.
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    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 [deg]F at sea level and 20 to 35 [deg]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.''
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    \5\ NTSB 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.
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D. FAA Response

    The FAA conducted ignition-prevention 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

[[Page 70926]]

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 Sec.  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 cost-effectiveness 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 Sec.  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 Sec.  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 Sec.  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 non-aerospace 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

[[Page 70927]]

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.
---------------------------------------------------------------------------

    \6\ The 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.
---------------------------------------------------------------------------

    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\
---------------------------------------------------------------------------

    \7\ Auxiliary 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.
---------------------------------------------------------------------------

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

[[Page 70928]]

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.
---------------------------------------------------------------------------

    \8\ The 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 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.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \9\ Rather 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.
---------------------------------------------------------------------------

    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 Sec.  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.

[[Page 70929]]



                   Table 1.--Summary of Proposed Rules
------------------------------------------------------------------------
                                 Description of
           14 CFR                   proposal             Applies to
------------------------------------------------------------------------
25.1, 25.2..................  Expand applicability  Applicants for TCs,
                               to current holders    and changes to
                               of TCs, STCs, and     those TCs for
                               certain               transport category
                               manufacturers.        airplanes.
                              Amend Sec.   25.2 to   Manufacturers of
                               make reference to     certain airplane
                               the proposed          models.
                               subpart I..
25.981......................  Revise paragraph (b)  Applicants for
                               to specify limits     future TCs and
                               on fuel tank          design changes to
                               flammability.         those certificates.
                              Add paragraph (c) to
                               restate current
                               option of providing
                               ignition mitigation
                               means (IMM)..
                              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    TCs, and design
                               of the subpart.       changes to those
                                                     TCs for transport
                                                     category airplanes.
                                                     Manufacturers of
                                                     certain airplane
                                                     models.
25.1815.....................  Require flammability  TC holders.
                               exposure analysis
                               of all fuel tanks
                               within 150 days
                               after effective
                               date. If below 7
                               percent no
                               flammability
                               reduction required.
                               Compliance with
                               Sec.   25.981(d) to
                               define ALI required.
                              If above 7 percent    Large transport
                               and in fuselage and   category passenger
                               normally emptied,     airplanes, with
                               must develop          passenger capacity
                               service               of 30 or more or a
                               instructions to       payload of 7500 lbs
                               meet Sec.             or more (original
                               25.981(b), (c) and    TC or later
                               (d).                  increase).
                              If above 7 percent
                               and other tank
                               type, must develop
                               service
                               instructions to
                               incorporate IMM
                               (meet Sec.
                               25.981(c), or
                               reduce flammability
                               to 7 percent)..
                              Specific compliance
                               dates for each
                               Boeing and Airbus
                               airplane model.
                               Other models within
                               24 months.
25.1817.....................  Require flammability  Auxiliary tank STC
                               exposure analysis     holders for large
                               of all fuel tanks     transport category
                               installed under STC   passenger
                               within 12 months      airplanes, with
                               after effective       passenger capacity
                               date.                 of 30 or more or a
                              Require impact         payload of 7500
                               assessment of fuel    lbs. or more
                               tanks installed by    (original TC or
                               STCs, and (for        later increase).
                               pending and future
                               applicants) other
                               STCs affecting fuel
                               tank flammability,
                               on IMM or FRM
                               developed by TC
                               holder under Sec.
                               25.1815 to
                               determine if any
                               ALI has been
                               violated 6 months
                               after FAA approval
                               of ALI submitted by
                               TC holders under
                               Sec.   25.1815 or
                               before
                               certification,
                               whichever is later..
                              Require development   Applicants for
                               of service            future STCs or
                               instructions to       amendments to TCs
                               correct designs       that affect fuel
                               that compromise ALI   tank system or IMM/
                               defined by TC         FRM.
                               holder under Sec.
                               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.
25.1819.....................  Requires IMM or FRM   Pending
                               for any fuel tank     certification
                               on a passenger        projects.
                               airplane with a      Pre Amendment 102.
                               flammability level
                               that exceeds 7
                               percent. Fuel tanks
                               located in the
                               fuselage and
                               normally emptied
                               must meet Sec.
                               25.981(b) level.
                               Other fuel tanks
                               must not exceed 7
                               percent.
                              Requires compliance   Post Amendment 102.
                               with Sec.
                               25.981(c).
25.1821.....................  Requires any          Manufacturers of
                               affected airplanes    certain airplane
                               produced after a      models.
                               certain date to
                               incorporate IMM or
                               FRM.
Appendix 25 K...............  Establishes           Applicants for
                               performance,          approval of
                               reliability and       flammability
                               reporting             reduction means.
                               requirements for
                               flammability
                               reduction means.
Appendix 25 L...............  Defines flammability  Any person required
                               analysis method and   to perform
                               input parameters      flammability
                               that must be used     analysis.
                               in the analysis.
91.1509, 121.917, 125.509,    Require retrofit of   U.S. certificate
 129.117.                      IMM or FRM into       holders and foreign
                               large airplanes       persons operating
                               with high             U.S.-registered
                               flammability fuel     large transport
                               tanks. Require        category passenger
                               large transport       airplanes.
                               category airplanes
                               manufactured after
                               specific dates to
                               have IMM or FRM in
                               high flammability
                               fuel tanks. Require
                               incorporation of
                               ALI into the
                               maintenance program.
------------------------------------------------------------------------

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

[[Page 70930]]

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 Sec.  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 Sec.  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 ongoing-
airworthiness 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 Sec.  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 Sec.  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 Sec.  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

[[Page 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 
type-certificated 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 Sec.  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 all-cargo 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

[[Page 70932]]

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, Sec.  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.

[[Page 70933]]

    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 Sec.  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 Sec.  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 all-cargo 
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.
---------------------------------------------------------------------------

    \10\ These are cargo handlers and other persons who are 
typically carried on cargo-only airplanes to assist in the cargo 
operations.
---------------------------------------------------------------------------

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 Sec.  
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.
---------------------------------------------------------------------------

    \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 Sec.  25.1815 
to reference Amendment 25-102 as the appropriate standard for fuel 
tanks on these airplanes other than those located in the fuselage.
---------------------------------------------------------------------------

    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

[[Page 70934]]

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.
---------------------------------------------------------------------------

    \12\ With 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 Sec.  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.
---------------------------------------------------------------------------

    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 Sec.  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 Sec.  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.
---------------------------------------------------------------------------

    \13\ This 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.
    \14\ As indicated in Appendix L, we intend to incorporate the 
users manual by reference into the final rule.
---------------------------------------------------------------------------

    The Monte Carlo method,\15\ as commonly understood by scientists, 
is

[[Page 70935]]

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.
---------------------------------------------------------------------------

    \15\ History 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 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.
---------------------------------------------------------------------------

    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 Sec.  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

[[Page 70936]]

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

[[Page 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 Sec.  
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 
Sec.  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--
    <bullet> Flammability exposure of the unheated aluminum wing tank,
    <bullet> Cooling rate,
    <bullet> Limits on heat input,
    <bullet> Limits on use of high volatility fuels such as JP-4,
    <bullet> Quantity of engine bleed air flow that is used for 
inerting,
    <bullet> Limits on penetrations of the fuel tank,
    <bullet> Limits on any changes to fuel management that may affect 
FRM,
    <bullet> 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 Sec.  
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 Sec. Sec.  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,

[[Page 70938]]

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 Sec.  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

[[Page 70939]]

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.
---------------------------------------------------------------------------

    \16\ Flight-Testing of the FAA Onboard Inert Gas Generation 
System on an Airbus A320, DOT/FAA/AR-03/58, dated June 2004.
---------------------------------------------------------------------------

    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
------------------------------------------------------------------------
                                           Service instruction submittal
                  Model                                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:
    <bullet> Part 91, General Operating and Flight Rules;
    <bullet> Part 121, Operating Requirements: Domestic Flag and 
Supplemental Operation;
    <bullet> 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
    <bullet> 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.

[[Page 70940]]



                             Table 3.--New Subparts for Parts 91, 121, 125, and 129
----------------------------------------------------------------------------------------------------------------
                                        Part 121 new/relocated   Part 125 new/relocated   Part 129 new/relocated
  Part 91 new/relocated rules within    rules  within proposed   rules  within proposed   rules  within proposed
          proposed subpart K                  subpart Y                subpart M                subpart B
----------------------------------------------------------------------------------------------------------------
Sec.   91.1501, Applicability (new)..  Sec.   121.901,          Sec.   125.501,          Sec.   129.101,
                                        Applicability.           Applicability.           Applicability.
Sec.   91.1503, Reserved.............  Sec.   121.903,          Sec.   125.503,          Sec.   129.103,
                                        Reserved.                Reserved.                Reserved.
Sec.   91.1505, fuel tank system       Sec.   121.905,          Sec.   125.505, Fuel     Sec.   129.105,
 maintenance program.                   Electrical wiring        tank system inspection   Electrical wiring
                                        interconnection          program.                 interconnection
                                        systems (EWIS)                                    systems (EWIS)
                                        maintenance program.                              maintenance program.
Sec.   91.1507, Repairs assessment     Sec.   121.907, Fuel     Sec.   125.507, Repairs  Sec.   129.107, Fuel
 for pressurized fuselages (formerly    tank system              assessment for           tank system
 Sec.   91.401(a)).                     maintenance program.     pressurized fuselages    maintenance program.
                                                                 (formerly Sec.
                                                                 125.248(a)).
Sec.   91.1509, Reserved.............  Sec.   121.909,          Sec.   125.509,          Sec.   129.109,
                                        Reserved.                Reserved.                Reserved.
Sec.   91.1511, Reserved.............  Sec.   121.911,          Sec.   125.511,          Sec.   129.111,
                                        Reserved.                Reserved.                Reserved.
                                       Sec.   121.913, Aging    .......................  Sec.   129.113,
                                        airplane inspections                              Supplemental
                                        and records reviews                               inspections for U.S.-
                                        (formerly Sec.                                    registered aircraft
                                        121.368).                                         (formerly Sec.
                                                                                          129.16).
                                       Sec.   121.915, Repairs  .......................  Sec.   129.115, Repairs
                                        assessment for                                    assessment for
                                        pressurized fuselages                             pressurized fuselages
                                        (formerly Sec.                                    (formerly Sec.
                                        121.370(a)).                                      129.32(a)).
Sec.   91.1513, Reserved.............  Sec.   121.917,          .......................  Sec.   129.117, Aging
                                        Supplemental                                      airplane inspections
                                        inspections (formerly                             and records reviews
                                        Sec.   121.370(a).                                for U.S.-registered
                                                                                          aircraft (formerly
                                                                                          Sec.   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.
---------------------------------------------------------------------------

    \17\ A part 91 operator would send the relevant information to 
either their principal inspector or Flight Standards District 
Office, as applicable.
---------------------------------------------------------------------------

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 FAA-
approved MEL. The MEL contains a list of equipment that may be 
inoperative for a defined period of time. Under Sec.  91.213 and 
similar regulations, the airplane may be dispatched with inoperative 
equipment in accordance with the Master Minimum Equipment List (MMEL).

[[Page 70941]]

    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:
    <bullet> Aging Aircraft Program (Widespread Fatigue Damage 
(proposal),
    <bullet> Aging Airplane Safety (interim final rule), and
    <bullet> 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.
---------------------------------------------------------------------------

    \18\ A copy of the AIA report is included in the docket for this 
rulemaking.
---------------------------------------------------------------------------

3. FAA Oversight Office
    We are also requiring affected persons to submit various compliance 
materials to the FAA Oversight Office, defined in proposed Sec.  
25.1803(c). The FAA Oversight Office is the aircraft

[[Page 70942]]

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.
---------------------------------------------------------------------------

    \19\ Our 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 Sec.  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).
---------------------------------------------------------------------------

    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.
    <bullet> Minimum standards required in the interest of safety for 
the design and performance of aircraft;

[[Page 70943]]

    <bullet> Regulations and minimum standards in the interest of 
safety for inspecting, servicing, and overhauling aircraft; and
    <bullet> 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--
    <bullet> New safety standards for the design of transport category 
airplanes, and
    <bullet> 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 Sec.  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:
    <bullet> Develop the design and the data for STCs to install fuel 
tank inerting systems,
    <bullet> Develop and incorporate a maintenance plan into the 
existing maintenance programs,
    <bullet> 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:

------------------------------------------------------------------------
                                                          Present value
     Documents required to show                          discounted cost
  compliance with the proposed rule    One-time pages    (in millions of
                                                             $2005)
------------------------------------------------------------------------
Specifications for Fuel Tank STC....             8,000               2.7
Manuals (Flight Manuals, Operations,            12,000               2.7
 and Maintenance) for Fuel Tank STC.
Production for Fuel Tank STC........               500               0.4
Documentation for FAA/EASA                       1,000              13.4
 Certification......................
                                     -------------------
    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--
    <bullet> 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;
    <bullet> Evaluate the accuracy of the agency's estimate of the 
burden;
    <bullet> Improve the quality, utility, and clarity of the 
information to be collected; and
    <bullet> Minimize the burden of the collection of information on 
those who are to respond using appropriate automated, electronic, 
mechanical, or

[[Page 70944]]

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 $]
------------------------------------------------------------------------
                                                          Present value
                                                              of the
                     Source of cost                         compliance
                                                              costs
------------------------------------------------------------------------
Engineering Redesign...................................              $64
Retrofitting Costs.....................................              377
Production Costs.......................................              133
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.
    <bullet> Final rule would be effective January 1, 2006.
    <bullet> Discount rate is 7 percent.
    <bullet> Fully burdened labor rate for an aviation engineer is $125 
an hour.
    <bullet> Fully burdened labor rate for an aviation mechanic is $85 
an hour.
    <bullet> 3,804 airplanes would be retrofitted between 2008 and 
2016.
    <bullet> No airplane scheduled to be retired before 2016 would be 
retrofitted.
    <bullet> Cost of aviation fuel is $1.00 per gallon.\20\
---------------------------------------------------------------------------

    \20\ The 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.
---------------------------------------------------------------------------

    <bullet> The type of accident that would be prevented is a 
catastrophic accident in

[[Page 70945]]

which all die and the airplane is destroyed.
    <bullet> 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)
    <bullet> Boeing and Airbus airplanes have equal risk of an 
explosion.
    <bullet> The explosion rate calculation does not include explosions 
caused by terrorist activity.
    <bullet> An explosion is estimated to occur every 60 million hours 
of flight by heated center wing tank airplanes.
    <bullet> The value of a statistical fatality averted is $3 million.
    <bullet> An average of 140 passengers and crew are on a Boeing or 
Airbus airplane.
    <bullet> The cost to investigate a catastrophic accident is $8 
million.
    <bullet> 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.
---------------------------------------------------------------------------

    \21\ These 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.
---------------------------------------------------------------------------

    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]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                          SFAR 88               Present values             Benefit/cost
                     Discount rate  (percent)                           Value of       effectiveness  ----------------------------------      ratio
                                                                        fatality         (percent)         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,

[[Page 70946]]

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]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                          SFAR 88               Present values             Benefit/cost
                     Discount rate  (percent)                           Value of       effectiveness  ----------------------------------      ratio
                                                                        fatality         (percent)         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]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                          SFAR 88               Present values             Benefit/cost
                     Discount rate  (percent)                           Value of       effectiveness  ----------------------------------      ratio
                                                                        fatality         (percent)         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
--------------------------------------------------------------------------------------------------------------------------------------------------------


[[Page 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]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                         Present values
                                                                        Value of          SFAR 88     --------------------------------------------------
                      Discount rate (percent)                           fatality       effectiveness                                       Benefit/cost
                                                                                         (percent)         Benefits          Costs       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]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                      Benefit/cost ratios
                                                                                          SFAR 88     --------------------------------------------------
                      Discount rate (percent)                           Value of       effectiveness                                       Production-
                                                                        fatality         (percent)       Retrofitted       Production      retrofitted
                                                                                                          (percent)        (percent)        (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

[[Page 70948]]

 
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 
N-registered 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

[[Page 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:
    <bullet> Are the requirements in the proposed regulations clearly 
stated?
    <bullet> Do the proposed regulations contain unnecessary technical 
language or jargon that interferes with their clarity?
    <bullet> Would the regulations be easier to understand if they were 
divided into more (but shorter) sections?
    <bullet> 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 Sec.  25.1 by adding new paragraphs (c) and (d) to read as 
follows:


Sec.  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 Sec.  25.2 by adding a new paragraph (d) to read as 
follows:


Sec.  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 Sec.  25.981 by revising paragraphs (b) and (c) and adding 
paragraphs (d) and (e) to read as follows:


Sec.  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

[[Page 70950]]

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 Sec.  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


Sec.  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 Sec.  21.101 of this 
subchapter.
    (3) [Reserved]
    (4) Holders of type certificates and their licensees producing new 
airplanes.


Sec.  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).


Sec.  25.1805-25.1813  [Reserved]

Fuel Tank Flammability


Sec.  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 all-cargo 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
------------------------------------------------------------------------
                                           Service instruction submittal
                 Model--                               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.
------------------------------------------------------------------------


[[Page 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.


Sec.  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 all-cargo 
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 Sec.  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

[[Page 70952]]

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 Sec.  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
----------------------------------------------------------------------------------------------------------------
                                                                                            Design changes and
                                        Flammability exposure    Impact assessment plan   service  instructions
                                            analysis plan                                          plan
----------------------------------------------------------------------------------------------------------------
STC and Field Approval Holders.......  60 days after            60 days after the date   240 days after the date
                                        [effective date of       identified in Sec.       identified in Sec.
                                        final rule].             25.1815(d) for the       25.1815(d) for the
                                                                 applicable airplane      applicable airplane
                                                                 model.                   model.
STC and ATC Applicants...............  60 days after            60 days after the date   240 days after the date
                                        [effective date of       identified in Sec.       identified in Sec.
                                        final rule] or before    25.1815(d) for the       25.1815(d) for the
                                        the certificate is       applicable airplane      applicable airplane
                                        issued, whichever        model or before the      model or before the
                                        occurs later.            certificate is issued,   certificate is issued,
                                                                 whichever occurs later.  whichever occurs
                                                                                          later.
----------------------------------------------------------------------------------------------------------------


[[Page 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.


Sec.  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.


Sec.  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[deg]F (standard day plus 
21[deg]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.

[[Page 70954]]

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 
Sec.  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 Sec.  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 pre-flight 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 self-rescue (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.

[[Page 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 Sec.  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 non-flammable 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 
airplane-specific 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 
<plus-minus> 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 
<plus-minus> 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 [deg]F. LFL decreases from sea level value with 
increasing altitude at a rate of 1 [deg]F per 808 feet.
    (ii) UFL at sea level = flash point temperature of the fuel at 
sea level plus 63.5 [deg]F. UFL decreases from the sea level value 
with increasing altitude at a rate of 1 [deg]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
----------------------------------------------------------------------------------------------------------------
                                                                            Temperature in deg F
                                                           -----------------------------------------------------
                         Parameter                           Ground ambient    Cruise ambient   Fuel flash point
                                                               temperature       temperature           (FP)
----------------------------------------------------------------------------------------------------------------
Mean Temp.................................................             59.95               -70               120
Neg 1 std dev.............................................             20.14                 8                 8
Pos 1 std dev.............................................             17.28                 8                 8
----------------------------------------------------------------------------------------------------------------


[[Page 70956]]

    (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

[[Page 70957]]

to be chosen as a random value from the following Gaussian curve:

                Table 3.--Landing Outside Air Temperature
------------------------------------------------------------------------
                                                        Landing outside
                      Parameter                         air temperature
                                                            [deg]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
------------------------------------------------------------------------
                                                           OAT drop
                      Parameter                       temperature [deg]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
------------------------------------------------------------------------
                                  Maximum acceptable  Maximum acceptable
                                      Monte Carlo         Monte Carlo
                                   average fuel tank   average fuel tank
  Minimum number of flights in       flammability        flammability
      Monte Carlo analysis          exposure (%) to     exposure (%) to
                                        meet 3%             meet 7%
                                     requirements        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 Sec.  91.1 by adding a new paragraph (d) to read as 
follows:


Sec.  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


Sec.  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.


Sec. Sec.  91.1503-91.1507  [Reserved]


Sec.  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 
Sec. Sec.  25.1815, 25.1817, or 25.1819 of this chapter.
    (b) New Production Airplanes. Except in accordance with Sec.  
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 Sec.  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 Sec. Sec.  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 Sec.  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.

[[Page 70958]]



                                                     Table 1
----------------------------------------------------------------------------------------------------------------
                                       Compliance date for 50%
                Model                          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     Within 7 years after the effective date of this
                                        the effective date of    amendment.
                                        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 Sec.  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 Sec. Sec.  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 Sec. Sec.  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.


Sec.  91.410  [Redesignated as Sec.  91.1505]

    11. Redesignate Sec.  91.410 as new Sec.  91.1505.


Sec.  91.410  [Added and Reserved]

    12. A new Sec.  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 Sec.  121.1 by adding a new paragraph (g) to read as 
follows:


Sec.  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


Sec.  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.


Sec.  121.1103-121.1115  [Reserved]


Sec.  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 Sec. Sec.  25.1815, 25.1817, or 25.1819 of this 
chapter.
    (b) New Production Airplanes. Except in accordance with Sec.  
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

[[Page 70959]]

is approved by the FAA Oversight Office.
    (3) Except in accordance with Sec.  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 Sec. Sec.  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 Sec.  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
----------------------------------------------------------------------------------------------------------------
                                       Compliance date for 50%
                Model                          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     Within 7 years after the effective date of this
                                        the effective date of    amendment.
                                        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 Sec.  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 Sec. Sec.  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 Sec. Sec.  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


Sec.  121.368  [Redesignated as Sec.  121.1105]

    16. Redesignate 121.368 as new Sec.  121.1105.


Sec.  121.368  [Added and Reserved]

    17. A new Sec.  121.368 is added and reserved.


Sec.  121.370  [Redesignated as Sec.  121.1107]

    18. Redesignate Sec.  121.370 as new Sec.  121.1107.


Sec.  121.370  [Added and Reserved]

    19. A new Sec.  121.370 is added and reserved.


Sec.  121.370a  [Redesignated as Sec.  121.1109]

    20-21. Redesignate Sec.  121.370a as new Sec.  121.1109.


Sec.  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 Sec.  125.1 by adding a new paragraph (e) to read as 
follows:


Sec.  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.

[[Page 70960]]

Subpart M--Continued Airworthiness and Safety Improvements


Sec.  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.


Sec. Sec.  125.503-125.507  [Reserved]


Sec.  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 Sec. Sec.  25.1815, 25.1817, or 25.1819 of this 
chapter.
    (b) New Production Airplanes. Except in accordance with Sec.  
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 Sec.  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 Sec. Sec.  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 Sec.  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
----------------------------------------------------------------------------------------------------------------
                                       Compliance date for 50%
                Model                          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     Within 7 years after the effective date of this
                                        the effective date of    amendment.
                                        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 Sec.  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 Sec. Sec.  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 Sec. Sec.  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.


Sec.  125.248  [Redesignated as Sec.  125.505]

    25. Redesignate Sec.  125.248 as new Sec.  125.505.

[[Page 70961]]

Sec.  125.248  [Added and Reserved]

    26. A new Sec.  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 Sec.  129.1 by revising paragraph (b), and adding a new 
paragraph (d) to read as follows:


Sec.  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, Sec. Sec.  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 Sec.  129.1 
through Sec.  129.15 and Sec.  129.17 through Sec.  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


Sec.  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.


Sec.  Sec.  129.103-129.115  [Reserved]


Sec.  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 Sec. Sec.  25.1815, 25.1817, or 25.1819 
of this chapter.
    (b) New Production Airplanes. Except in accordance with Sec.  
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 Sec.  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 Sec. Sec.  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 Sec.  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
----------------------------------------------------------------------------------------------------------------
                                       Compliance date for 50%
                Model                          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.

[[Page 70962]]

 
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     Within 7 years after the effective date of this
                                        the effective date of    amendment.
                                        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 Sec.  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 Sec. Sec.  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 Sec. Sec.  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.


Sec.  129.16  [Redesignated as Sec.  129.109]

    31. Redesignate Sec.  129.16 as new Sec.  129.109.


Sec.  129.16  [Added and Reserved]

    32. A new Sec.  129.16 is added and reserved.


Sec.  129.32  [Redesignated as Sec.  129.107]

    33. Redesignate Sec.  129.32 as new Sec.  129.107.


Sec.  129.32  [Added and Reserved]

    34. A new Sec.  129.32 is added and reserved.


Sec.  129.33  [Redesignated as Sec.  129.105]

    35. Redesignate Sec.  129.33 as new Sec.  129.105.


Sec.  129.33  [Added and Reserved]

    36. A new Sec.  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


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