Reduction of Fuel Tank Flammability in Transport Category Airplanes

62 Pages·2016·0.46 MB·English

Monday,
July 21, 2008
Part III
Department of
Transportation
Federal Aviation Administration
14 CFR Parts 25, 26, 121 et al.
Reduction of Fuel Tank Flammability in
Transport Category Airplanes; Final Rule
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42444 Federal Register/Vol. 73, No. 140/Monday, July 21, 2008/Rules and Regulations
DEPARTMENT OF TRANSPORTATION this discussion is related information 4. Specific Airplane Models
about the docket, privacy, and the 5. Wing Tanks
Federal Aviation Administration handling of proprietary or confidential 6. Auxiliary Fuel Tanks
7. Existing Horizontal Stabilizer Fuel
business information. We also discuss
Tanks
14 CFR Parts 25, 26, 121, 125, and 129 how you can get a copy of this final rule
8. Foreign Persons/Air Carriers Operating
and related rulemaking documents.
[Docket No. FAA–2005–22997; Amendment U.S. Registered Airplanes
Nos. 25–125, 26–2, 121–340, 125–55, and Authority for Rulemaking 9. Airplanes Operated Under §121.153
129–46] 10. International Aspects of Production
The FAA’s authority to issue rules Requirements
RIN 2120–AI23 regarding aviation safety is found in D. Requirements for Manufacturers and
Title 49 of the United States Code. Holders of Type Certificates,
Reduction of Fuel Tank Flammability in
Subtitle I, Section 106 describes the Supplemental Type Certificates and
Transport Category Airplanes authority of the FAA Administrator. Field Approvals
1. General Comments About Design
AGENCY: Federal Aviation Subtitle VII, Aviation Programs,
Approval Holder (DAH) Requirements
Administration (FAA), DOT. describes in more detail the scope of the
2. Flammability Exposure Level
ACTION: Final rule, request for agency’s authority. Requirements for New Airplane Designs
comments. This rulemaking is promulgated 3. Flammability Exposure Requirements for
under the authority described in Current Airplane Designs
SUMMARY: This final rule amends FAA Subtitle VII, Part A, Subpart III, Section 4. Continued Airworthiness and Safety
regulations that require operators and 44701, ‘‘General requirements.’’ Under Improvements
manufacturers of transport category that section, the FAA is charged with E. Flammability Exposure Requirements
airplanes to take steps that, in promoting safe flight of civil aircraft in for Airplane Operators
combination with other required air commerce by prescribing minimum 1. General Comments About Applicability
to Existing Airplanes
actions, should greatly reduce the standards required in the interest of
2. Authority to Operate With an
chances of a catastrophic fuel tank safety for the design and performance of
Inoperative FRM, IMM or FIMM
explosion. The final rule does not direct aircraft; regulations and minimum 3. Availability of Spare Parts
the adoption of specific inerting standards in the interest of aviation 4. Requirement That Center Fuel Tank be
technology either by manufacturers or safety for inspecting, servicing, and Inert Before First Flight of the Day
operators, but establishes a overhauling aircraft; and regulations for F. Appendix M—FRM Specifications
performance-based set of requirements other practices, methods, and 1. Fleet Average Flammability Exposure
that set acceptable flammability procedures the Administrator finds Levels
exposure values in tanks most prone to necessary for safety in air commerce. 2. Inclusion of Ground and Takeoff/Climb
Phases of Flight
explosion or require the installation of This regulation is within the scope of
3. Clarification of Sea Level Ground
an ignition mitigation means in an that authority because it prescribes
Ambient Temperature
affected fuel tank. Technology now • New safety standards for the design
4. Deletion of Proposed Paragraph M25.2
provides a variety of commercially of transport category airplanes, and (Showing Compliance)
feasible methods to accomplish these • New requirements necessary for 5. Deletion of ‘‘Fuel Type’’ From List of
vital safety objectives. safety for the design, production, Requirements in Proposed Paragraph
DATES: These amendments become operation and maintenance of those M25.2(b)
September 19, 2008. Send your airplanes, and for other practices, 6. Latent Failures
comments by January 20, 2009. The methods, and procedures related to 7. Identification of Airworthiness
incorporation by reference of the those airplanes. Limitations
8. Catastrophic Failure Modes
document listed in the rule is approved Table of Contents 9. Reliability Reporting
by the Director of the Federal Register I. Executive Summary G. Appendix N—Fuel Tank Flammability
as of September 19, 2008. A. Statement of the Problem Exposure and Reliability Analysis
FORFURTHERINFORMATIONCONTACT: If B. Reducing the Chance of Ignition 1. General
you have technical questions about this C. Reducing the Likelihood of an Explosion 2. Definitions
action, contact Michael E. Dostert, FAA, After Ignition 3. Input Parameters
Propulsion/Mechanical Systems Branch, II. Background 4. Verification of ‘‘Flash Point
A. Summary of the NPRM Temperature’’
ANM–112, Transport Airplane
B. Related Activities H. Critical Design Configuration Control
Directorate, Aircraft Certification C. Differences Between the NPRM and the Limitations (CDCCL)
Service, 1601 Lind Avenue, SW., Final Rule 1. Remove Requirement
Renton, Washington 98057–3356; III. Discussion of the Final Rule 2. Clarification on Responsibility for Later
telephone [phone], facsimile A. Summary of Comments Modifications
(425) 227–1320; e-mail: B. Necessity of Rule 3. Limit CDCCL’s to Fuel Tanks That
[email protected]. Direct any legal 1. Estimates/Conclusions Supporting Need Require FRM or IMM
questions to Doug Anderson, ANM–7, for Rule 4. STC Holders May Not Have Data to
2. Additional Research Needed Comply
FAA, Office of Regional Counsel, 1601
3. Consistent Safety Level With Other I. Methods of Mitigating the Likelihood of
Lind Avenue, SW, Renton, WA 98057–
Systems a Fuel Tank Explosion
3356; telephone [phone]; 4. Human Errors 1. Alternatives to Inerting
facsimile (425) 227–1007, e-mail 5. Explosion Risk Analysis 2. Inerting Systems Could Create Ignition
[email protected]. 6. Special Certification Review Process vs. Sources
S3 SUPPLEMENTARYINFORMATION: Later in Rulemaking 3. Instruments to Monitor Inerting Systems
ULE this preamble under the ADDITIONAL 7. Flammability Reduction Means (FRM) 4. Risk of Nitrogen Asphyxiation
with R INFORMATION section, we discuss C. EAffpepcltiicvaebnielistsy 56.. WDeafrinniitnigo nP loafc ‘a‘Irndesr t’’
C71 how you can comment on a certain 1. Airplanes With Fewer Than 30 Seats 7. Use of Carbon Dioxide
D1P portion of this final rule and how we 2. Part 91 and 125 Operators 8. Environmental Impact of FRM
RO will handle your comments. Included in 3. All-Cargo Airplanes 9. Current FRMs Fail to Meet Requirements
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Federal Register/Vol. 73, No. 140/Monday, July 21, 2008/Rules and Regulations 42445
10. FRM Based on Immature Technology nine fatalities).2While the accident transport category airplane designs of all
J. Compliance Dates investigations of the TWA, Philippine major manufacturers has shown that
1. Part 26 Design Approval Holder Airlines and Thai Airlines accidents unanticipated failures and maintenance
Compliance Dates failed to identify the ignition source that errors will continue to generate
2. Operator Fleet Retrofit Compliance Dates
caused the explosion, the investigations unexpected ignition sources. Since
K. Cost/Benefit Analysis
found several similarities. In each manufacturers completed their SFAR 88
1. Security Benefits
2. Likelihood of Future Explosions in instance: ignition prevention reviews, we have
Flight 1. The weather was warm, with an had reports of potential ignition sources
3. Costs to Society of Future Accidents outside air temperature over 80 °F; (including unsafe conditions) that were
4. Value of a Prevented Fatality 2. The explosion occurred on the not identified in the SFAR 88 reviews.
5. Cost Savings if Transient Suppression ground or soon after takeoff; and For example:
Units (TSUs) are not Required 3. The explosion involved empty or • We issued AD 2006–06–14 to
6. Corrections About Boeing Statements nearly empty tanks that contained require the inspection of fuel quantity
7. 757 Size Category residual fuel from the previous fueling. indicating probes within the fuel tanks
8. Number of Future Older In-Service
Additionally, investigators were able of Airbus A320 airplanes to prevent an
Airplanes Overestimated
to conclude that the center wing fuel ignition source due to sparks that could
9. Revisions to the FRM Kit Costs
tank in all three airplanes contained be created following a lightning strike.
10. Revisions to the Labor Time to Retrofit
FRM Components flammable vapors in the ullage (that This failure mode was not identified as
11. Retrofitting Costs per Airplane portion of the fuel tank not occupied by a possible ignition source in the SFAR
12. Percentage of Retrofits Completed liquid fuel) when the fuel tanks 88 analysis presented to the FAA.
During a Heavy Check exploded. This was also the case with • We issued AD 2006–12–02
13. Number of Additional Days of Out-of- the Avianca airplane. following a report of an improperly
Service Time to Complete a Retrofit A system designed to reduce the installed screw inside the fuel pump
14. Economic Losses From an Out-of- likelihood of a fuel tank fire, or mitigate housings of A320 airplanes that could
Service Day the effects of a fire should one occur, loosen and fall into the pump’s
15. Updated FRM Weight Data
would have prevented these four fuel electrical windings. This could create a
16. Updated Fuel Consumption Data
17. Updated Fuel Cost Data tank explosions. spark and ignite fuel vapors in the
18. Cost of Inspections A statistical evaluation of these pump. The ignited vapors could then
19. Inspection and Maintenance Labor accidents has led the FAA to project exit the fuel pump housing, enter the
Hours that, unless remedial measures are fuel tank through the hole created when
20. Daily Check taken, four more United States (U.S.) the screw fell out of the housing, and
21. Spare Parts Costs registered transport category airplanes cause a fuel tank explosion. This failure
22. Air Separation Model (ASM) will likely be destroyed by a fuel tank mode was not identified as a possible
Replacement explosion in the next 35 years. Although ignition source in the SFAR 88 analysis
L. Miscellaneous we cannot forecast precisely when these presented to the FAA.
1. Harmonization • We received an in-service report on
2. Part 25 Safety Targets accidents will occur, computer
a Boeing 777 that was operated for over
IV. Regulatory Notices and Analyses modeling that has been an accurate
30 days with an open vent hole between
V. The Amendment predictor in the past indicates these
the center wing fuel tank and the wheel
events are virtually certain to occur. We
I. Executive Summary well of the airplane. During
believe at least three of these explosions
maintenance, a vent hole cover used to
A. Statement of the Problem are preventable by the adoption of a
facilitate venting of the tank was
comprehensive safety regime to reduce
Fuel tank explosions have been a both the incidence of ignition sources inadvertently left off. This was not
constant threat with serious aviation developing and the likelihood of the discovered until a flight occurred where
safety implications for many years. fuel tank containing flammable fuel the tank was fueled to a level where the
Since 1960, 18 airplanes have been vapors. fuel spilled from the tank into the wheel
damaged or destroyed as the result of a well during pitching up of the airplane
fuel tank explosion. Two of the more B. Reducing the Chance of Ignition for takeoff. Since the airplane brakes
recent explosions—one involving a To address the first part of this routinely exceed temperatures that
Boeing 747 (Trans World Airways comprehensive safety regime, we have could ignite fuel vapors and the wheels
(TWA) Flight 800) off Long Island, New taken several steps to reduce the are retracted into the wheel well, the
York in 1996 and the other, a Boeing chances of ignition. Since 1996, we have open vent port could have allowed
727 terrorist-initiated explosion imposed numerous airworthiness ignition of fuel vapors in the center tank
(Avianca Flight 203) in Bogota´, requirements (including airworthiness and a fuel tank explosion. This type of
Columbia in 19891—occurred during directives or ‘‘ADs’’) directed at the maintenance error was also not
flight and led to catastrophic losses elimination of fuel tank ignition identified as providing a possible
(including the deaths of 337 sources. Special Federal Aviation ignition source during the SFAR 88
individuals). Two other recent Regulation No. 88 of 14 Code of Federal safety reviews.
• On May 5, 2006, an explosion
explosions on airplanes operated by Regulations (CFR) part 21 (SFAR 88; 66
occurred in the wing fuel tank of a
Philippine Airlines and Thai Airlines FR 23086, May 7, 2001) requires the
Boeing 727 in Bangalore, India, while
occurred on the ground (resulting in detection and correction of potential
the airplane was on the ground. This
system failures that can cause ignition.
event occurred after a modification to
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RUL in the Bogota´accident, the NTSB determined the explosions, our review of the current recurring inspections had been
with ‘‘bomb explosion did not compromise the structural implemented to prevent possible arcing
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RO of the airplane.’’ accident in Bangkok in 2001. information indicates that the identified
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42446 Federal Register/Vol. 73, No. 140/Monday, July 21, 2008/Rules and Regulations
AD action was inadequate to prevent the Technology now exists that can several pending type-certification
formation of an ignition source in the prevent ignition of flammable fuel applications, including the Boeing 7875
fuel tank and that the change intended vapors by reducing their oxygen and Airbus A350, also have to meet
to improve safety caused premature concentration below the level that will these requirements.
wear of the sleeving and an unsafe support combustion. By making the We acknowledge that these
condition. Premature wear of Teflon vapors ‘‘inert,’’ we can significantly requirements are costly and have
sleeving on the Boeing 737 has also reduce the likelihood of an explosion adopted these steps only after spending
been reported, resulting in AD action to when a fire source is introduced to the several years researching the most cost-
modify the design and replace the fuel tank. FAA-developed prototype effective ways to prevent fuel tank
existing sleeving. This failure mode was onboard fuel tank inerting systems have explosions in cooperation with
not identified as a possible ignition been successfully flight tested on Airbus engineers and other experts from the
source in the SFAR 88 analysis A320 and Boeing 747 and 737 airplanes. affected industry. Those efforts have
presented to the FAA. We have also approved inerting systems resulted in the development of fuel-
• We also received a report that for the Boeing 747 and 737 airplanes, inerting technology that is vastly
during a recent certification program and two airplanes of each model type cheaper than originally thought.
test, an ignition source developed in the have performed as expected during In contrast, the loss of a single, fully
fuel pumps causing pump failure. These airline in-service evaluations. Boeing loaded large passenger airplane in flight,
pumps had been designed to meet the plans to install these systems on all new such as a Boeing 747 or Airbus A380,
most stringent requirements of SFAR 88 production airplanes. would result in death and destruction
and Amendment 25–102 to 14 CFR Given that ignition sources will causing societal loss of at least $1.2
25.981 (issued concurrently with SFAR develop, the chances of a fuel tank billion (based on costs of prior
88), yet the pump failed in a manner explosion naturally correlate with the calamities). We estimate that
that allowed a capacitor to arc to the exposure of the tank to flammable compliance with this new rule will
pump enclosure and create an ignition vapors. The requirements in this final prevent between one and two accidents
source. The applicant has since rule mitigate the effects of such of some type (for analytical purposes we
conducted a design review that has flammability exposure and limit it to assume the accidents would involve
resulted in numerous modifications to acceptable levels by mandating the ‘‘average’’ airplanes with ‘‘average’’
the pump’s design. installation of either a Flammability passenger loads) over 35 years.6In
• Following the TWA 800 accident, Reduction Means (FRM) or an Ignition addition to the direct costs of such an
the risk of uncontrolled fire adjacent to Mitigation Means (IMM).3In either case, accident, we now recognize that, in the
the fuel tanks causing a fuel tank the technology has to adhere to post-9/11 aviation environment, the
explosion was identified as an unsafe performance and reliability standards public could initially assume that an in-
condition. In 2006, we issued a MD–80 that are set by us and contained in flight fuel tank explosion is the result of
AD (AD 2006–15–15) to prevent worn Appendices M and N to Title 14 Code terrorist actions. This could cause a
of Federal Regulations (CFR) part 25.
insulation on wires from arcing at the substantial immediate disruption of
This final rule amends the existing
auxiliary hydraulic pump, which could flights, similar to what occurred in
airworthiness standards contained in 14
result in a fire in the wheel well of the Britain on August 10, 2006, due to the
CFR 25.981 to require all future type
airplane. The AD required inspections discovery of a terrorist plot.7This could
certificate (TC) applicants for transport
to validate the pump wire integrity as have an immediate and substantial
category airplanes to reduce fuel tank
well as incorporating sleeving on adverse economic effect on the aviation
flammability exposure to acceptable
portions of the wires. In April 2008, we levels. It also amends 14 CFR part 26 industry as a whole.
The FAA’s safety philosophy is to
received reports of improper means of ‘‘Continued Airworthiness and Safety
address aviation safety threats whenever
compliance being used regarding the Improvements’’4to require TC holders
practicable solutions are found,
requirements of AD 2006–15–15. to develop FRM or IMM for many large
especially when dealing with intractable
Human error in completing the turbine-powered transport category
and catastrophic risks like fuel tank
procedures required by the AD resulted airplanes with high-risk fuel tanks.
explosions that are virtually certain to
in airplanes being operated without the Finally, it amends 14 CFR parts 121, 125
needed safety improvements. and 129 to require operators of these
Based on the above examples, we airplanes to incorporate the approved 5This airplane model already includes a FRM in
its design that the applicant intends to show will
have concluded that we are unlikely to FRM or IMM into the fleet and to keep meet today’s final rule, so no additional
identify and eradicate all possible them operational. We estimate that modifications will be required.
sources of ignition. approximately 2,700 existing Airbus 6Although Boeing has committed to installing
compliant FRM in all future production airplanes,
and Boeing airplanes operating in the
C. Reducing the Likelihood of an regardless of this rule, operators could deactivate
Explosion After Ignition United States as well as about 2,300 the systems unless this rulemaking is adopted. The
newly manufactured airplanes that enter final regulatory evaluation includes the costs and
To ensure safety, therefore, we must U.S. airline passenger service will be benefits of these actions for newly produced Boeing
also focus on the environment that affected. Fuel tank system designs in and Airbus airplanes.
permits combustion to occur in the first 7Flight schedules in Britain were significantly
disrupted due to flight cancellation of all flights
place. Many transport category airplanes 3FRM consist of systems or features installed to into Heathrow Airport and 30 percent of all short-
are designed with heated center wing reduce or control fuel tank flammability to haul flights out of Heathrow Airport for one day
tanks in which the fuel vapors are acceptable levels. IMM is based upon mitigating the (according to Secretary of State for Transport
flammable for significant portions of effects of a fuel vapor ignition in a fuel tank so that Douglas Alexander). The day after the event, the
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RUL addresses the risk of a fuel tank AC 25.981–2 for additional information. Airways stated that it cancelled 1,280 flights
with explosion by reducing the likelihood 4Part 26 was added to the Code of Federal between August 10–17 due to the discovery of the
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RO tank. subject. Ryanair said it cancelled a total of 265 flights.
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Federal Register/Vol. 73, No. 140/Monday, July 21, 2008/Rules and Regulations 42447
occur. Thus, now that solutions are Appendix N) to part 25 that provides a Lastly, the proposal would require
reasonably cost effective, we have method for calculating overall and affected operators to incorporate FRM or
determined that it is necessary for safety warm day fuel tank flammability IMM for high-risk fuel tanks in their
and in the public’s best interest to adopt exposure. Where the required analyses existing fleet of affected airplane
these requirements. indicated that the fuel tank has an models. The proposal would have
average flammability exposure below 7 applied to operators of airplanes under
II. Background
percent, we anticipate no changes parts 91, 125, 121, and 129. Operators
A. Summary of the NPRM would be required. However, for the would also have to revise their
other fuel tanks, manufacturers would maintenance and inspection programs
On November 23, 2005, the FAA
be required to develop design to incorporate the airworthiness
published in the Federal Register the
modifications to support a retrofit of the limitations developed under the NPRM.
Notice of Proposed Rulemaking (NPRM)
airplane fuel tanks. Under the NPRM, We also proposed strict retrofit
entitled ‘‘Reduction of Fuel Tank
the average flammability exposure of deadlines, which were premised on
Flammability in Transport Category
any affected wing tank would have to be prompt compliance by manufacturers
Airplanes’’ (70 FR 70922). This NPRM
reduced to no more than 7 percent. In with their compliance plans.
is the basis for this final rule.
addition, for any normally emptied fuel The NPRM contains the background
In the NPRM, we proposed steps to be
tank (including auxiliary fuel tanks) and rationale for this rulemaking and,
taken by manufacturers and operators of
located in whole or in part in the except where we have made revisions in
transport category airplanes to
fuselage, flammability exposure was to this final rule, should be referred to for
significantly reduce the chances of a
be reduced to 3 percent, both for the that information.
catastrophic fuel tank explosion. The
proposal followed seven years of overall fleet average and for operations B. Related Activities
on warm days.
intensive research by the FAA and On November 28, 2005, the FAA
industry into technologies designed to We also proposed to set more published a Notice of Availability of
make fuel tanks effectively inert. stringent safety levels for certain Proposed Advisory Circular (AC)
Inerting reduces the amount of oxygen critically located fuel tanks in most new 25.981–2A, Fuel Tank Flammability,
in the fuel tank vapor space so that type designs, while maintaining the and request for comments in the Federal
combustion cannot take place if there is current, general standard under §25.981 Register (70 FR 71365). The notice
an ignition source. Although the NPRM for all other fuel tanks. The expectation announced the availability of a
did not specifically direct the adoption was that the design of most normally proposed AC that would set forth an
of inerting technology, it did propose a emptied and auxiliary tanks located in acceptable means, but not the only
performance-based set of requirements whole or in part in the fuselage of means, of demonstrating compliance
for reducing fuel tank flammability to an transport category airplanes would need with the provisions of the airworthiness
acceptably safe level. to incorporate some form of FRM or standards set forth in the NPRM. On
We proposed regulatory changes to IMM. March 21, 2006, the FAA published a
require manufacturers and operators to In Appendix M to part 25, we notice that extended the comment
reduce the average fuel tank proposed to adopt detailed period as a result of an extension of the
flammability exposure in affected fleets. specifications for all FRM, if they were NPRM’s comment period to May 8, 2006
The main premise of the proposal was used to meet the flammability exposure (71 FR 14281).
that a balanced approach to fuel tank limitations. These additional
safety was needed that provides both requirements were designed to ensure C. Differences Between the NPRM and
prevention of ignition sources and the effectiveness and reliability of FRM, the Final Rule
reduction of flammability of the fuel mandate reporting of performance As a result of the comments received
tanks. While the focus of the NPRM was metrics, and provide warnings of and our own continued review of the
on airplanes used in passenger possible hazards in and around fuel proposals in the NPRM, we have made
operations, we requested comments on tanks. several changes to the proposed
whether the new requirements should We also proposed that TC holders for regulatory text. The majority of these
also be applied to all-cargo airplanes. specific airplane models with high changes will be discussed in the
We also proposed changes to expand flammability exposure fuel tanks be ‘‘Discussion of the Final Rule’’ section
the coverage of part 25 by making required to develop design changes and below. The following is a summary of
manufacturers generally responsible for service instructions to facilitate the main differences between the NPRM
the development of service information operators’ installation of IMM or FRM. and this final rule.
and safety improvements (including Manufacturers of these airplanes would 1. Design Approval Holders. The
design changes) where needed to ensure also have to incorporate these design design approval holder (DAH)
the continued airworthiness of changes in airplanes produced in the requirements proposed in the NPRM as
previously certificated airplanes. This future. In addition, design approval subpart I of part 25 are now contained
change was proposed to ensure that holders (TC and STC holders) and in new part 26. This was done to
operators would be able to obtain applicants would have to develop harmonize with the regulatory structure
service instructions for making airworthiness limitations to ensure that of other international airworthiness
necessary safety improvements in a maintenance actions and future authorities. We also revised the
timely manner. modifications do not increase applicability for the retrofit requirement
As to fuel tank flammability flammability exposure above the limits so the DAH requirements do not apply
specifically, we proposed to require specified in the proposal. These design to airplanes manufactured before 1992.
S3 manufacturers, including holders of approval holders would have to submit The effect of this change is that DAHs
E
UL certain airplane TCs and of auxiliary binding compliance plans by a specified will not have to develop FRM or IMM
R
with fuel tank supplemental type certificates date, and these plans would be closely for many older airplane models that do
C71 (STCs), to conduct a flammability monitored by the design approval not have significant remaining useful
D1P exposure analysis of their fuel tanks. We holders’ FAA Oversight Offices to life in passenger operations. We revised
RO proposed a new Appendix L (now ensure timely compliance. the compliance times for DAHs to
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42448 Federal Register/Vol. 73, No. 140/Monday, July 21, 2008/Rules and Regulations
develop and make available service operation of airplanes with high Airlines (AEA), Boeing, Cathay Pacific
instructions for FRM or IMM by flammability fuel tanks produced after Airways (Cathay), Delta Air Lines
replacing specific compliance dates 2009 unless they are equipped with (Delta) and FedEx stated that the
with a compliance time of 24 months FRM or IMM. This requirement parallels historical accident rate of 1 accident
after the effective date of this rule for all the proposed production cut-in every 60 million fleet operating hours
affected airplane models. We have also requirement, but also applies to foreign was too high. Most of these commenters
made some changes, discussed later, to manufactured airplanes. Finally, instead recommended a rate of 1 accident per
the compliance planning sections of the of requiring retrofit of high flammability 140 million hours. Their proposed rate
DAH requirements. auxiliary fuel tanks, we prohibit is based on the number of accidents and
2. Auxiliary Fuel Tanks. We have installation of auxiliary fuel tanks after the total fleet hours for heated center
learned that few auxiliary fuel tanks 2016 unless they comply with the new wing tank (HCWT) airplanes through
installed under STCs and field requirements of §25.981. 2005 (3 accidents over 430 million
approvals remain in service, and we hours). Several of these commenters
III. Discussion of the Final Rule
need to obtain additional information to also noted that this rate is closer to the
decide whether the risks from these A. Summary of Comments conservative estimate in the MITRE
tanks justify retrofit requirements. Corporation’s assessment of the FAA’s
The FAA received over 100 comment
Therefore, we have removed the accident prediction/avoidance model (1
letters to the proposed rule and
requirements for an FRM or IMM retrofit accident every 160 million hours).9
guidance material. These letters covered
for these tanks. Boeing proposed a rate of 1 accident
a wide spectrum of topics and range of
3. Impact Assessments. We limited every 100 million hours. Boeing’s
responses to the rulemaking package,
the requirement for impact assessments analysis also started with the number of
which will be discussed more fully
for auxiliary fuel tanks to airplanes with accidents and the total fleet hours for
below. While there was much support
high flammability tanks for which an HCWT airplanes through 2005.
for the general intent of the rule changes
FRM is required (i.e., Heated Center However, Boeing recognized that some
and the guidance material, there were
Wing Tank airplanes). of the improvement since 2001 may be
several requests for changes and for
4. All-Cargo Airplanes. We retained attributable to the FAA/industry focus
clarification.
the proposal to exclude all-cargo on ignition prevention and concluded
airplanes from the requirement to B. Necessity of Rule that the rate of 1 accident every 100
retrofit high flammability tanks with million hours more accurately
1. Estimates/Conclusions Supporting
FRM or IMM. However, we added a represents the pre-TWA 800 rate.
requirement that when any airplane that Need for Rule FedEx stated that, from a historical
has an FRM or IMM is converted from In the NPRM and its supporting basis, 140 million hours would be a
passenger use to all-cargo use, these documents, we noted several estimates correct mean time between accidents.
safety features must remain operational. and conclusions that we used to However, FedEx noted that a more
We also added a requirement that newly determine the necessity and content of conservative estimate closer to 100
manufactured all-cargo airplanes must this rule. We received comments on the million hours would still be acceptable.
meet the same requirements as newly following assumptions: In a related comment, ATA
manufactured passenger airplanes. We • The historical accident rate for questioned our use of flight hours as the
revised §25.981 to remove the exclusion heated center wing tank (HCWT) measure of exposure to risk. ATA noted
of all-cargo airplanes so that any newly airplanes is 1 accident per 60 million that two of the historical accidents did
certificated transport category airplane, hours of flight (before implementing not occur in flight. Therefore, flight
regardless of the type of operation, must corrective actions following TWA 800). hours may understate exposure and
meet the same safety standards. • That SFAR 88 and other corrective overstate risk. ATA concluded that
5. Part 91 Operators. The proposed actions would prevent 50 percent of these accidents support the use of block
rule would have applied to operators future fuel tank explosions. hours or some other measure that
under part 91, which is limited to • That Boeing and Airbus airplanes accounts for time on the ground (and
private use operations. However, the have an equal risk of an explosion. would lower the accident rate by about
final rule does not include part 91 • That a HCWT, depending upon the 16 percent).
requirements. airplane model and its mode of We agree that the accident rate used
6. Retrofit Requirements for operation, is explosive 12 to 24 percent in the NPRM was too high and needs
Operators. We have added a provision of the time. adjustment. While the rate of 1 accident
for air carrier operators that allows a one • That the rate of accidents directly every 140 million hours is correct if you
year extension in the compliance time correlates to flammability exposure. only use the total fleet hours for HCWT
to retrofit of their affected fleets if they Based on the comments received, we airplanes through 2005, it fails to
revise their operations specifications have changed the historical accident consider the beneficial effects of FAA/
and manuals to use ground conditioned rate estimate to 1 accident per 100 industry action following the TWA 800
air8when it is available. Instead of million hours. This change does not accident. Since that accident, we have
affect our conclusion that the historical issued many ADs to address specific
requiring retrofit for all airplanes with
accident rate for HCWT airplanes findings of unsafe conditions that could
high flammability fuel tanks, we revised
supports the need for this rule. As for produce fuel tank ignition sources. In
the operating rules to prohibit operation
the other estimates and conclusions, we addition, the Fuel Tank Safety Rule, of
of these airplanes in passenger service
have not changed these in the final rule. which SFAR 88 was a part, was issued
after 2016 unless an FRM or IMM is
in 2001 to establish a systematic process
S3 installed. This approach gives operators a. Historical (pre-TWA 800) Accident for identifying and eliminating ignition
ULE the option of converting these airplanes Rate
R to all-cargo service. We also prohibit the
with Airbus, the Air Transport Association 9The Mitre assessment of the FAA accident
D1PC71 co8n‘t‘rGorloleudn adi rc ounseddit itoon veedn atiilra’’t ei st hteem apireprlaatnuer ec abin (AAsTsoAc)i,a Atiloans koaf AAsirilai nPeasc i(fAicl aAskiral)i,n tehse poinfr etthdheiec Idtniooictnik amel tRe fteohgro utdhlaoitsloo rrguyyl eEimsv aianlkucialnutgido (enDd oa ancsud Am ispe panvet anidlaixb lHe
RO while the airplane is parked between flights. (AAPA), the Association of European Number FAA–2005–22997–3).
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Federal Register/Vol. 73, No. 140/Monday, July 21, 2008/Rules and Regulations 42449
sources. Many of the improvements effectiveness rates of 25 and 75 percent). flammability and the associated increase
resulting from these actions have been ATA stated that the 50 percent in the likelihood of a fuel tank
implemented in the transport airplane effectiveness rate was without basis or explosion. We based the SFAR 88
fleet, and the improved safety record explanation and recommended a rate of effectiveness estimates on the HCWT
since TWA 800 is largely attributable to 90 percent. Airbus recommended an fleet as a whole. We did not differentiate
them. While the commenters effectiveness rate in the range of 75 to among airplane models based upon
acknowledge that these actions have 90 percent. If these higher rates are design differences that could affect the
been effective at preventing future used, ATA and Airbus noted the safety likelihood of an ignition source forming.
accidents, most of them failed to reduce benefits of the proposed rule are AEA, Airbus, Frontier Airlines
their proposed historical rate insufficient to justify the costs, and they (Frontier), the Air Safety Group UK,
accordingly to address these benefits. In requested that we withdraw the NPRM. Singapore Airlines (Singapore), BAE
contrast, Boeing’s recommended rate Predicting the effectiveness of ignition Systems (BAE), TDG Aerospace (TDG)
considers the benefits of these actions prevention actions is challenging, since disagreed with this proposal and argued
(which we calculate covers about 170 many ignition sources are the result of that the risk of an explosion is lower for
million hours). human error, which cannot be precisely Airbus airplanes. These commenters
We believe that an accident rate of 1 predicted or quantitatively evaluated. noted that fuel tank designs for those
per 100 million hours is an accurate Despite extensive efforts by the FAA airplanes that experienced a fuel tank
calculation of the historical accident and industry to prevent ignition explosion are at least a decade older
rate before implementation of post-TWA sources, we continue to learn of new than Airbus’ designs. Airbus argued that
800 ignition prevention actions. ignition sources. Some of these ignition its airplanes use newer technology and
Therefore, we used this rate in sources are attributable to failures on design philosophies that have
developing this final rule and its the part of engineering organizations to incorporated the lessons learned from
supporting documents. However, this identify potential ignition sources and prior designs. BAE and two individuals
change does not affect our conclusion provide design changes to prevent them. suggested that we address fuel tank
that the historical accident rate for Others are attributable to actions by flammability by issuing ADs to address
HCWT airplanes supports the need for production, maintenance, and other specific design shortfalls in the two
this rule. We continue to believe that operational personnel, who airplane types that have experienced
the risk of an accident is too high. inadvertently compromise wiring and fuel tank explosions (i.e., the Boeing 737
Several commenters referred to the equipment producing ignition sources. and 747 series airplanes).
rate in the MITRE Corporation’s report Regardless of the causes, we believe that While we did note differences
(1 accident every 160 million hours). ignition prevention actions, while between the designs and technologies
This rate includes operations of necessary, are insufficient to eliminate used by Boeing and Airbus, we
airplanes without HCWT. ignition sources. concluded that the risk of an explosion
Recommendations resulting from Based on the recently discovered was equal for Boeing and Airbus
MITRE’s review included a suggestion ignition sources discussed earlier, we airplanes based on similarities in their
that only fleet hours from airplanes with continue to believe that an assumed fuel tank designs and service history.
HCWT be used in the accident effectiveness rate of 50 percent is We found that both manufacturers have
prediction model. We agreed with this reasonable and appropriate. In its study similar problematic fuel tank design
recommendation and have adjusted the on SFAR 88 effectiveness, Sandia features. For example, air conditioning
accident rate accordingly. National Laboratories concluded that equipment is located below the center
Finally, we do not agree with ATA’s our estimate of 50 percent was wing tank in both manufacturers’
conclusion that the use of flight hours reasonable, and the value of 75 percent designs (and HCWT have flammability
to predict future accidents results in an effectiveness assumed in the initial exposure well above that of a
overstated risk. Both the past accident Aviation Rulemaking Advisory conventional unheated aluminum wing
rate and the future predicted number of tank). Likewise both manufacturers
Committee (ARAC) report was overly
accidents were based upon the number locate fuel gauging systems with
optimistic. While the report of the
of flight hours of airplanes with high capacitance measuring probes inside the
ARAC Fuel Tank Inerting
flammability fuel tanks, and in both fuel tank, and associated wiring to the
Harmonization Working Group10
cases the number of flight hours does probes enters the fuel tank from outside.
initially assumed an effectiveness of 75
not include ground time. The ratio of These wires are co-routed with high-
percent, the report was later amended to
flight time to ground time is unlikely to energy wiring to other airplane systems
use a range of effectiveness between 25
change significantly in the future that have sufficient energy to cause an
to 75 percent because of the uncertainty
because the average flight length and the ignition source inside the fuel tanks.
in predicting the effectiveness.
amount of time spent on the ground Finally, since ATA did not submit Finally, high-energy electrical fuel
before and after each flight are unlikely any data to substantiate that a higher pumps are located within the fuel tanks
to change significantly. Therefore, effectiveness rate is more reasonable, we and are fuel-cooled and manufactured
whether past and future accident rates believe the post-SFAR 88 service by the same component suppliers.
are stated in terms of flight time only or experience supports the use of a range Arcing of the pump could cause a spark
flight time plus ground time, the of effectiveness between 25 to 75 inside the fuel tank or could create a
projected future accident rates would percent and a median value of 50 hole at the pump connector, causing a
predict the same number of accidents percent. fuel leak and an uncontrolled fire
over any given time period. outside of the tank.
c. Boeing and Airbus Airplanes Have an As for the service history and design
S3 b. SFAR 88 Effectiveness Rate Equal Risk of an Explosion reviews of Airbus airplanes, we found
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RUL In the NPRM and its supporting We concluded that all airplanes with numerous situations that indicate a risk
with documents, we estimated that SFAR 88 HCWT had similar levels of fuel tank of an explosion similar to those aboard
D1PC71 wtaonukl edx pprleovseionnt s5 (0a lptehrocuegnht owf ef uatlusore fuel 10Document Number FAA–22997–6 in the docket Bo•eiTngh ea ierlpelcatnriecsa, li nboclnuddiinngg s: traps used
RO conducted a sensitivity analysis using for this rulemaking. on Airbus airplanes have been reported
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42450 Federal Register/Vol. 73, No. 140/Monday, July 21, 2008/Rules and Regulations
to degrade due to corrosion; the bonding the level of safety improvement that can explosions, or that the reduction in
jumpers used by Boeing are made of a be achieved by this rule from the FAA’s flammability exposure would be on the
different material that does not corrode. intended ‘‘order of magnitude’’ (factor of order of a factor of 10. Therefore, we do
• All fuel pumps on Boeing airplanes 10) to a safety improvement in the range not believe that these refinements
are being modified to incorporate of only a factor of 7.7 to 2.7, depending change the overall conclusion that
ground fault power interrupters, on the model used. Airbus also objected certain fuel tanks that are affected by
whereas only pumps that can arc to our conclusion that a HCWT, this rule have significantly higher
directly into the fuel tank ullage are depending upon the airplane model and flammability exposure than
being modified to incorporate ground its mode of operation, is explosive 12 to conventional unheated aluminum wing
fault power interrupters on Airbus 24 percent of the time. Airbus requested tanks. No change has been made to the
airplanes. that this be corrected to reflect the latest final rule as a result of these comments.
• The safety assessments conducted industry estimates for Airbus products
e. Accidents Directly Correlate to
by both manufacturers resulted in very (i.e., 8 to 12 percent) and 16 to 18
Flammability Exposure
similar numbers of ignition sources that percent for other manufacturers.
required modifications to their We acknowledge that the Airbus did not agree with the
airplanes. flammability exposure data cited in the assumption that the rate of accidents
• After the SFAR 88 assessments NPRM may not reflect current values. directly correlates to flammability
were completed, we learned that fuel However, Boeing and Airbus submitted exposure. Airbus contended that the
quantity indicating probes within the those data to us as part of the SFAR 88 risk of ignition source development
fuel tanks of Airbus A320 airplanes reviews. While we agree with Airbus must also be considered when
could be an ignition source due to that more recent information has evaluating the benefits of flammability
sparks that could be created following a indicated lower flammability for reduction.
lightning strike. This resulted in the HCWTs, we do not agree that the more We agree with Airbus that the overall
issuance of AD 2006–06–14. recent values should be used since the risk of a fuel tank explosion includes
• After the SFAR 88 assessments manufacturers have not submitted a both the potential for an ignition source
were completed, we learned that the validated analysis using the revised and the likelihood that the fuel tank will
improper installation of a screw inside flammability assessment techniques (as be flammable when an ignition source
the fuel pumps of Airbus A320 defined in §25.981) to support its occurs. There may be differences in the
airplanes could result in the screw figures. Changes to the method for likelihood of an ignition source
loosening and falling into the pump calculating fuel tank flammability, such occurring between different airplane
electrical windings. This could create a as airplane ground times used in the types, but these differences would be
spark and ignite vapors in the pump Monte Carlo analysis required by very difficult to quantify. We have no
that could exit the fuel pump housing Appendix N may result in additional statistically significant, validated data
into the fuel tank through the hole variations in flammability calculations. that could be used to establish rates of
created when the screw fell out of the Since flammability reduction was first development of ignition sources for
housing. This resulted in the issuance of considered by the aviation industry, the different airplane types. As discussed in
AD 2006–12–02. flammability values quoted by airplane the Sandia report, there is a wide
The recent discovery of the ignition manufacturers have varied considerably. variation in the predicted rate of
sources in Airbus A320 airplanes is These variations were the result of the ignition sources developing in fuel
evidence that unforeseen failures will method used to calculate the tanks and there is no industry
occur in the future that can result in flammability of the fuel tanks and more agreement on the rate that should be
ignition sources on Airbus airplanes. accurate fuel tank temperature data used for individual airplane designs. In
The Airbus fleet has significantly fewer based upon flight tests. For example, the addition, recent service history shows
flight hours than Boeing airplanes and, first ARAC determined values ranged there have been a number of ignition
as the Airbus airplanes age, we expect from 10 to 50 percent for generic sources that have developed following
to see more unforeseen failures. airplanes equipped with HCWT. After the TWA 800 accident in both Airbus
Therefore, based on design similarities the conclusion of this activity, Airbus and Boeing airplane models.
and service history, we see no reason to was quoted in Air Safety Week as stating Given this lack of data and consensus
differentiate between Airbus and Boeing the A310 HCWT having a flammability on ignition source risks, we continue to
airplanes. This rule requires all affected exposure of 4 percent. In 2001, as part believe that correlating accident rates
manufacturers to determine the fuel of the SFAR 88 compliance, Airbus with flammability exposure is the most
tank flammability exposure of their submitted flammability values to the appropriate analytical approach.
airplanes by assessing them against European Aviation Safety Agency
2. Additional Research Needed
performance-based requirements that (EASA) and to us that ranged between
specify a flammability exposure that we 12 and 23 percent. Airbus, AAPA, AEA, EASA, Iberia
have determined provides an acceptable We recognize that as methods for Maintenance and Engineering (Iberia),
level of safety. Additional action is only measuring fuel tank flammability are Singapore and Virgin Atlantic Airways
required for those airplanes that do not refined, it is likely that calculated (Virgin) stated that this rulemaking is
meet the required level of fuel tank flammability exposure will also change. premature because the risks of
flammability safety. These refinements also apply to the additional fuel tank explosions are not
conventional unheated aluminum wing adequately defined. These commenters
d. ARAC Flammability Exposure Data
tanks that ARAC used as the baseline for argued that additional research is
Airbus and AEA both commented that determining an acceptable exposure. We necessary to better understand
S3 the ARAC flammability exposure data now know that the exposure of these flammability, SFAR 88 effectiveness and
E
UL cited in the NPRM are incorrect and tanks is considerably lower than the risks of additional explosions. In a
R
with need to be reduced based on updated originally estimated by ARAC. However, related comment, the International
C71 data developed by both Boeing and none of this new information changes Federation Victims of Aviation Accident
D1P Airbus. They said this reduction is the findings of ARAC that HCWTs have (IFVAA) stated that additional research
RO important since the lower data reduce significantly higher risk of fuel tank should be performed to identify
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Federal Register/Vol. 73, No. 140/Monday, July 21, 2008/Rules and Regulations 42451
technology that would completely holders are obliged to consider human further derived and applied on an
eliminate, not just reduce, fuel tank error during airplane design to mitigate individual type design basis.
flammability. errors. In addition, continuing We agree with the commenter that the
We think it would be a mistake to airworthiness instructions (e.g., assumed fuel air vapor mixture should
delay this rule to conduct additional maintenance manuals) highlight safety be based upon the individual fuel tank
research. Service history and the recent considerations where necessary. AEA design, and we included variations in
occurrences of ignition sources also contended that, in the 17 accidents the pressure and temperature of the fuel
described earlier demonstrate that the cited by the FAA in the NPRM, there is when developing the fuel tank
risk of future explosions remains no evidence that any were caused by the flammability model. This factor is
significant. In addition, we believe that introduction of an ignition source already accounted for in the Monte
additional research would not provide through human error. Finally, AEA Carlo method defined in Appendix N.
any useful information that would noted that human errors will always be As for the other assumptions offered by
change our finding that flammability a factor in aviation safety, particularly American Trans Air, they cannot be
reduction, in combination with the when introducing added complexity used in an analysis, because there is a
SFAR 88 measures, is needed to prevent such as an inerting system. wide variation in the possible values.
such explosions. As for IFVAA’s We agree with AEA that human errors 6. Special Certification Review Process
comment, we consider existing are not a new phenomenon and that the vs. Rulemaking
flammability reduction means highly introduction of new systems on
effective and sufficient to reduce the airplanes can have unintended American Trans Air commented that
risk of fuel tank explosions to an if an analysis identifies type designs
consequences resulting from human
acceptable level. While further research still found to have unacceptable risk
error. We also believe the safety benefits
might identify even better solutions, the after all SFAR 88 alterations have been
of FRM or IMM is warranted. Service
resulting delay would deprive the executed, an appropriate response to
history shows the current regulations do
public of the benefits of these currently address the remaining at-risk type
not provide an adequate mitigation of
available safety improvements. designs may be the use of the special
human errors for fuel tank systems.
certification review process. American
3. Consistent Safety Level With Other Ignition sources continue to occur even
Trans Air noted that there appears to be
Systems though designers have conducted
wide variability in the risk between type
analyses that concluded ignition sources
Airbus commented that SFAR 88 designs, and concluded that generalized
would not occur. Earlier in this
improvements, together with the current rulemaking is inappropriate at this time.
document, we discussed numerous
rate of occurrence, put fuel tank safety We do not agree that we should
ignition sources that have recently
on the order of one accident for every address each type design with
billion flight hours (i.e. 10¥9accidents developed in airplanes that had unacceptable flammability risk by
previously been shown by safety
per flight hour) which is consistent with special certification review and then by
assessments to have features that would
safety objectives of other critical an appropriate AD. Through careful
prevent ignition sources from
airplane systems.11Airbus argued that study, we have determined that the
developing. These ignition sources were
this rule requires fuel tanks to go to a flammability risk on many airplanes is
caused by errors in defining
higher level of safety than other critical too high. To address this risk, we have
assumptions in safety assessments, as
systems and that this is inconsistent created an objective design standard by
well as in the design, manufacture and
with the overall risk. which all airplanes can be measured. If
Application of existing safety maintenance of these airplanes. These airplanes currently meet this design
standards to prevent ignition sources events show that an additional layer of standard, no action will be required.
that are similar to those applied to other protection (in the form of FRM or IMM) The TC holder for those airplanes that
systems has not resulted in an is needed to prevent future fuel tank do not meet it will have to make only
acceptable level of safety, and we have explosions. those changes that bring that airplane
determined that limiting fuel tank 5. Explosion Risk Analysis model into compliance. We have
flammability is also needed. Fuel tank determined that the uncertainty
explosions are unacceptably occurring American Trans Air commented that involved in the elimination of ignition
at a rate greater than 10¥9per flight the assumptions made in the explosion sources requires reduced flammability
hour and the recent events described risk analysis were erroneous and not to acceptably reduced tank explosion
above show that unanticipated failures within the range of reasonable values. risk, and the most effective and efficient
continue to result in ignition sources American Trans Air recommended that way to address this issue is through the
within airplane fuel tanks. To protect a completely new analysis of the fuel rulemaking process.
the flying public, we have developed a tank explosion risk be undertaken. This
‘‘fail safe’’ policy for fuel tank safety new analysis should utilize widely 7. Flammability Reduction Means
that includes both ignition prevention accepted assumptions, including taking (FRM) Effectiveness
and flammability reduction to reduce into account: In the NPRM, we said lowering the
fuel tank explosion risk to an acceptable • The history of particular type flammability exposure of the affected
level. designs. fuel tanks in the existing fleet and
• The actual ignition risk potential limiting the permissible level of
4. Human Errors
(i.e., potential ignition sources not in flammability on new production
AEA stated that human errors are not the ullage are either exempted, or airplanes would result in an overall
new and should not be used to justify substantially discounted in the reduction in the flammability potential
S3 this rule. AEA pointed out that TC analysis). of these airplanes of approximately 95
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UL • Actual ignition energies, applying percent. Airbus and AEA commented
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with 11This is the quantitative probability measure these energies to the potential ignition that we overstated the potential benefits
D1PC71 io(mothnpeerr oi npb aaorbntl ee2 ’5b’ iaalsliir towhnoa)tr otthfe iranmne seissv esutnsaten dtdh iaanrtd §iss2. ‘5S‘e.e1xe3t rA0e9mC a enlyd sou•rcTehse. definitions and assumptions of ofafc ftloarm bmetawbeileinty 4 r eadnudc 7ti.o Tnh meye assauidre ws eb y a
RO 25.1309. fuel-air vapor mixtures that have been used a factor of 20 (95 percent) for the
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42452 Federal Register/Vol. 73, No. 140/Monday, July 21, 2008/Rules and Regulations
reduction in flammability exposure Exposure Evaluation Time (FEET). of the requirements of this rule are
achieved by reducing the flammability Historically, designers provide a safety minimal and do not warrant the cost.
of HCWT to 3 percent or less. They said margin in the design so that the design However, we do agree that the part 25
the subsequent reduction in limits are never exceeded, so we would requirements applicable to new type
flammability will be in the order of a expect the flammability to be below this designs should be the same for all
factor of three to five and not a factor level. transport category airplanes, regardless
of 20. Therefore, the number of Another consideration in using a 95 of size. The cost to design and produce
accidents prevented would percent effectiveness measure is the a new airplane to meet the flammability
consequentially be less than projected safety improvement noted during warm requirements is significantly less than
by the FAA. Airbus also said the FAA days. Without any FRM, a HCWT is that for existing airplanes since the
appears not to have considered the flammable about 50 percent of the time designers can optimize the performance
effectiveness of the FRM itself, which it during climb. Meeting both the 3 of the FRM or IMM and integrate it into
said is in the order of 67 to 87 percent percent warm day requirement and the the airplane design to minimize costs.
by latest industry estimates. Therefore, 3 percent reliability requirement results Therefore, §25.981 of this rule applies
Airbus suggests that the Initial in a flammability exposure of the tank to all transport category airplanes
Regulatory Evaluation (IRE) is of less than half of one percent during regardless of size.
incomplete and should be revised to climb. For an airplane with an initial
2. Part 91 and 125 Operators
include this key parameter. warm day flammability of 50 percent,
The 95 percent value used in the this is a 99 percent reduction in the The NPRM proposed that operators
NPRM was not based on the ratio of fuel flammability during climb. We, under parts 91, 121, 125, and 129
tank fleet average flammability exposure therefore, used the 95 percent incorporate FRM or IMM and keep it
before and after implementing the effectiveness for flammability reduction operational on their affected airplanes.
requirements of this rule. It was derived in the risk model for the final regulatory The AEA and Airbus asked that parts 91
by qualitatively evaluating the evaluation. and 125 operations be excluded and
effectiveness of an FRM in preventing cited corporate use airplanes as an
fuel tank explosions that would not be C. Applicability example of operations where the cost
prevented by ignition prevention 1. Airplanes With Fewer Than 30 Seats would far exceed the benefit. According
measures. to AEA and Airbus, the cost/benefit
When an FRM is installed on a fuel The proposed DAH requirements analysis for these airplanes, when
tank, it must meet both the 3 percent would apply (with some exclusions) to operated under part 91 or part 125,
fleet average flammability exposure and transport category turbine-powered would produce results similar to those
also the 3 percent warm day (specific airplanes approved for a passenger for all-cargo airplanes (which are
risk) flammability exposure capacity of 30 or more persons or a excluded from the retrofit requirements
requirements.12For the warm day maximum payload capacity of 7,500 of this rule).
requirement, the flammability exposure pounds or more. The UK Air Safety We recognize a distinction between
must be below 3 percent during ground Group disagreed with the proposed part 91 and part 125 operations, in that
and takeoff/climb conditions for those rule’s limited applicability because the part 91 does not allow commercial
days above 80 degrees F when the FRM design of fuel tank systems is similar for operations for compensation or hire,
is operational. These are the conditions both large and small airplanes. while part 125 does allow such
when fuel tanks tend to have the highest Therefore, it argued that the potential operations, as long as the operator does
flammability exposure and when the explosion hazard is equal. The not ‘‘hold out’’ to the public that they
accidents discussed earlier occurred. commenter also noted that EASA’s CS– are available for such operations (in
The combination of the warm day 25 regulation for Fuel Tank Ignition which case they would be required to
requirement and the fleet average Prevention does not make any operate as an air carrier). For example,
flammability requirement results in an distinction based on the number of many business jets are operated under
FRM with overall flammability passenger seats. part 91 if the operator does not receive
reduction benefits that are significantly We did not include smaller part 25 compensation for transporting
higher than those estimated by the airplanes in the DAH requirements of passengers (e.g., a corporate jet
commenters. Since the NPRM was this final rule because those airplanes transporting the corporation’s
issued, we have reviewed and approved generally do not have high flammability employees). On the other hand, charter
FRM designs and have found the tanks. While some parts of their fuel companies frequently operate under
performance exceeds the certification tank system designs are similar to those part 125 to transport sports teams and
limits. When the FRM is operating, the of larger airplanes, we do not agree that other groups for compensation.
fuel tanks are rarely flammable. So, the the overall architecture and the risk of While we recognize that private
major risk of fuel tank flammability a fuel tank explosion are equal. Data owners and operators may choose to
occurs when the system is inoperative submitted by manufacturers of smaller assume the risk of possible fuel tank
and this time is limited to a maximum part 25 airplanes as part of the SFAR 88 explosions, we see no reason why
of 1.8 percent of the Flammability analysis show that their airplanes persons flying on commercial charter
typically do not have fuel tanks located flights should be exposed to a greater
12The overall time the fuel tank is flammable within the fuselage contour, and would risk of a fuel tank explosion than
cannot exceed 3 percent of the Flammability not be considered high flammability passengers flying on airplanes operated
Exposure Evaluation Time (FEET), which is the fuel tanks. In most cases, cool fuel from under parts 121 and 129. Commercial
total time, including both ground and flight time, the wing tanks is drawn into the center charter passengers are in no better
ES3 cino npsriodpeorseedd i nA tphpee fnldamixm Na.b Ailsi tay paossrteisosnm oefn tth dise f3in ed wing box, so the overall flammability is position to recognize and accept the risk
RUL percent, if flammability reduction means (FRM) are low. In addition, these tanks are not of a fuel tank explosion than are air
with used, each of the following time periods cannot normally emptied, reducing the amount carrier passengers. Additionally, the risk
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