Document ID: FAA-2012-0187-0021
Agency: faa
Document Type: Proposed Rule
Title: Airworthiness Directives: The Boeing Company Airplanes
Posted Date: 2015-02-23T05:00Z

[Federal Register Volume 80, Number 35 (Monday, February 23, 2015)]
[Proposed Rules]
[Pages 9400-9414]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2015-03540]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2012-0187; Directorate Identifier 2011-NM-094-AD]
RIN 2120-AA64

Airworthiness Directives; the Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Supplemental notice of proposed rulemaking (NPRM); reopening of 
comment period.

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SUMMARY: We are revising an earlier proposed airworthiness directive 
(AD) for certain The Boeing Company Model 757 airplanes. The NPRM 
proposed to require modifying the fuel quantity indication system 
(FQIS) wiring or fuel tank systems to prevent development of an 
ignition source inside the center fuel tank. The NPRM was prompted by 
fuel system reviews conducted by the manufacturer. This action revises 
the NPRM by revising the applicability, including optional actions for 
cargo airplanes, and extending the compliance time. We are proposing 
this supplemental NPRM (SNPRM) to prevent ignition sources inside the 
center fuel tank, which, in combination with flammable fuel vapors, 
could result in fuel tank explosions and consequent loss of the 
airplane. Since these actions significantly change the corrective 
action options for cargo airplanes relative to the proposal in the 
NPRM, and because the cost estimate is significantly revised, we are 
reopening the comment period to allow the public the chance to comment 
on these proposed changes.

DATES: We must receive comments on this SNPRM by April 24, 2015.

ADDRESSES: You may send comments, using the procedures found in 14 CFR 
11.43 and 11.45, by any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
     Fax: 202-493-2251.
     Mail: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue SE., Washington, DC 20590.
     Hand Delivery: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue SE., Washington, DC 20590, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
    For service information identified in this AD, contact Boeing 
Commercial Airplanes, Attention: Data & Services Management, P. O. Box 
3707, MC 2H-65, Seattle, WA 98124-2207; telephone 206-544-5000, 
extension 1; fax 206-766-5680; Internet https://www.myboeingfleet.com. 
You may view this referenced service information at the FAA, Transport 
Airplane Directorate, 1601 Lind Avenue SW., Renton, WA. For information 
on the availability of this material at the FAA, call 425-227-1221. It 
is also available on the Internet at http://www.regulations.gov by 
searching for and locating Docket No. FAA-2012-0187.

Examining the AD Docket

    You may examine the AD docket on the Internet at http://www.regulations.gov by searching for and locating Docket No. FAA-2012-
0187; or in person at the Docket Management Facility between 9 a.m. and 
5 p.m., Monday through Friday, except Federal holidays. The AD docket 
contains this proposed AD, the regulatory evaluation, any comments 
received, and other information. The street address for the Docket 
Office (phone: 800-647-5527) is in the ADDRESSES section. Comments will 
be available in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT: Jon Regimbal, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office 
(ACO), 1601 Lind Avenue SW., Renton, WA 98057-3356; phone: 425-917-
6506; fax: 425-917-6590; email: jon.regimbal@faa.gov.

SUPPLEMENTARY INFORMATION: 

Comments Invited

    We invite you to send any written relevant data, views, or 
arguments about this proposed AD. Send your comments to an address 
listed under the ADDRESSES section. Include ``Docket No. FAA-2012-0187; 
Directorate Identifier 2011-NM-094-AD'' at the beginning of your 
comments. We specifically invite comments on the overall regulatory, 
economic, environmental, and energy aspects of this proposed AD. We 
will consider all comments received by the closing date and may amend 
this proposed AD because of those comments.
    We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We 
will also post a report summarizing each substantive verbal contact we 
receive about this proposed AD.

Discussion

    We issued an NPRM to amend 14 CFR part 39 by adding an AD that 
would apply to certain The Boeing Company Model 757 airplanes. The NPRM 
published in the Federal Register on March 1, 2012 (77 FR 12506). The 
NPRM proposed to require modifying the fuel quantity indication system 
(FQIS) wiring or fuel tank systems to prevent development of an 
ignition source inside the center fuel tank. We subsequently issued an 
NPRM (77 FR 33129, June 5, 2012) to reopen and extend the comment 
period for an additional 2 months.

Related Service Information Under 1 CFR Part 51

    We have reviewed Boeing Service Bulletin 757-28-0136, dated June 5, 
2014. This service information describes procedures for the built-in 
test equipment test/procedure (BITE check) specified in paragraph 
(h)(1) of this

[[Page 9401]]

supplemental NPRM. For information on the procedures and compliance 
times, refer to this service information. This service information is 
reasonably available; see ADDRESSES for ways to access this service 
information.

Comments

    We gave the public the opportunity to comment on the NPRM (77 FR 
12506, March 1, 2012). The following presents the comments received on 
the NPRM and the FAA's response to each comment.

Request To Withdraw NPRM (77 FR 12506, March 1, 2012): Unjustified by 
Risk

    Boeing and Airbus requested that we withdraw the NPRM (77 FR 12506, 
March 1, 2012). Airbus requested that we consider risk levels before 
pursuing anticipated ADs for similar models. Boeing's request was based 
on a determination that the risk posed by the FQIS is not high enough 
to warrant AD action. Boeing described the detailed design features 
that it considers make the failures contributing to the unsafe 
condition unlikely. Boeing added that its own numerical probability 
analysis of the average risk level due to the combination of failures 
required to cause a fuel tank explosion is on the order of one 
catastrophic event per billion flight hours. Boeing pointed out that 
this probability level would meet the certification standard for 
systems contained in section 25.1309(b) of the Federal Aviation 
Regulations (14 CFR 25.1309(b)). Boeing also pointed out that, because 
the Model 757 is out of production and has a limited remaining fleet 
life, the total risk of a catastrophic event occurring in the remaining 
fleet life is approximately 0.5 percent. Boeing also noted that if a 
conductive condition were to exist between the probes or wiring and 
structure, it would be identified by FQIS faults and therefore would 
not be latent for multiple flights.
    We disagree with the request to withdraw the NPRM (77 FR 12506, 
March 1, 2012). Average risk per flight hour and total fleet risk were 
not the safety criteria that drove the FAA to propose the AD. In 
addition to examining average risk and total fleet risk, the FAA 
examines the individual flight risk on the worst reasonably anticipated 
flights. FAA Transport Airplane Risk Assessment Methodology (TARAM) 
Policy Statement PS-ANM-25-05 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/4E5AE8707164674A862579510061F96B?OpenDocument&Highlight=ps-anm-25-05) 
calls for the FAA to assess individual flight safety risk in 
consideration of pre-existing hidden failure conditions and accounts 
for dispatch with inoperative equipment. The TARAM policy classifies a 
flight dispatch condition as ``reasonably anticipated'' if, in absence 
of corrective action, ten or more flights are expected to occur.
    Average risk is an arithmetic average of the risk of a given event 
during all operation of an aircraft fleet, regardless of whether the 
risk actually varies during the operation of the fleet. We use average 
risk analysis to assess whether a risk is acceptable when there is 
little or no variation in risk from flight to flight. Total fleet risk 
is the aggregate sum of all risk throughout a fleet during the 
remaining fleet life. Total fleet risk analysis is meaningful in 
assessing total societal risk, but it does not assess the variation in 
risk between flights or the risk on the worst anticipated flights. 
Individual flight risk as used by the FAA is an assessment of the 
specific safety risk that exists or will exist on the worst reasonably 
anticipated individual flights due to a given issue.
    Individual risk analysis is used by the FAA to determine whether 
the public's expectation for a reasonable level of safety on each 
transport airplane flight is met. An acceptable average risk level and 
acceptable total fleet risk do not ensure that all reasonably 
anticipated flights (flights with known inoperative equipment, flights 
with undetected failures, flights in less-than-ideal but approved and 
expected weather or operational conditions, etc.) will provide the 
minimum level of safety expected by the public. When the safety risk is 
concentrated on flights with a given pre-existing dispatch condition or 
expected operational condition, it is possible to have an unacceptable 
individual flight safety risk on the worst reasonably anticipated 
flights even when the average risk and total fleet risk are acceptable.
    In the case of this SNPRM, the risk due to the current Model 757 
FQIS design architecture is not spread equally among all of the flights 
conducted on the affected airplanes. Instead, the risk is concentrated 
almost entirely on the small subset of flights that occur with a latent 
failure condition pre-existing in the fuel tank. Flights with such a 
latent failure condition and flammable conditions in the center fuel 
tank have been judged by the FAA to be reasonably anticipated to occur 
based on the numerical probability analysis submitted by the 
manufacturer in response to Special Federal Aviation Regulation No. 88 
(``SFAR 88,'' Amendment 21-78, and subsequent Amendments 21-82 and 21-
83) (http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgFAR.nsf/0/EEFB3F94451DC06286256C93004F5E07?OpenDocument) and the flammability 
analysis submitted to support certification of Boeing's flammability 
reduction means (FRM), which Boeing refers to as a nitrogen generation 
system (NGS). For those reasonably anticipated flights, the probability 
of a catastrophic event (or individual flight safety risk) is the 
probability of an additional single failure in the related aircraft 
wiring or equipment sending a high energy signal onto the already 
compromised in-tank circuit(s). The individual flight safety risk of a 
catastrophic event on these flights is in excess of the FAA's threshold 
for an unsafe condition determination contained in the published TARAM 
Policy Statement PS-ANM-25-05 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/4E5AE8707164674A862579510061F96B?OpenDocument&Highlight=ps-anm-25-05).
    As discussed above, this risk of a catastrophic event on those 
flights is due to a single additional failure condition. The risk on 
those flights due to a single failure violates the FAA's general fail-
safe design requirements philosophy for transport airplanes. In 
general, we issue ADs in cases where reasonably anticipated flights 
with pre-existing failures (either due to latent failure conditions or 
allowable dispatch configurations) are vulnerable to a catastrophic 
event due to an additional foreseeable single failure condition. This 
is because the FAA considers operation of flights vulnerable to a 
potentially catastrophic single failure condition to be an excessive 
safety risk to the passengers on those flights. This SNPRM is 
consistent with that continued operational safety philosophy.
    In its comment, Boeing stated that the existing design meets the 
numerical probability requirements of section 25.1309(b) of the Federal 
Aviation Regulations (14 CFR 25.1309(b)), which requires safety 
analysis of systems. Boeing concluded that the existing system would 
need no further risk reduction to meet the requirements of that rule. 
We disagree with this conclusion. First, the existence of a general 
safety standard, even if met by a design, does not in and of itself 
preclude a determination that there is a specific unsafe condition. The 
recognition that compliance with an existing regulation may not be 
sufficient to ensure safety is specifically addressed in type 
certification by section 21.21(b)(2) of the Federal Aviation 
Regulations (14 CFR 21.21.(b)(2)) and

[[Page 9402]]

has often led to changes in regulations to address newly recognized 
unsafe conditions. Second, because Boeing mentioned only that rule, we 
infer that Boeing may be suggesting that section 25.1309(b) of the 
Federal Aviation Regulations (14 CFR 25.1309(b)) is the most relevant 
safety analysis standard applicable to the FQIS. As discussed above, 
even if later changes to section 25.981 of the Federal Aviation 
Regulations (14 CFR 25.981) are not considered and only the original 
certification basis for the Model 757 is applied, there are safety 
standards more specific to powerplant installations including fuel 
tanks and FQIS than section 25.1309(b) of the Federal Aviation 
Regulations (14 CFR 25.1309(b)).
    The original certification basis for Model 757 airplanes included 
section 25.901(c) of the Federal Aviation Regulations (14 CFR 
25.901(c)) (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFar.nsf/FARSBySectLookup/25.901) at Amendment 25-40. According to 
that subsection, ``For each powerplant and auxiliary power unit 
installation, it must be shown that no single failure or malfunction or 
probable combination of failures will jeopardize the safe operation of 
the airplane. . . .'' (The FQIS is considered to be part of the 
powerplant installation in accordance with the definition in section 
25.901(a) of the Federal Aviation Regulations (14 CFR 25.901(a)).) 
Section 25.901(c) of the Federal Aviation Regulations (14 CFR 
25.901(c)) sets a more stringent applicable standard than that of 
section 25.1309(b) of the Federal Aviation Regulations (14 CFR 
25.1309(b)) for catastrophic failure conditions that are due to latent 
failure conditions combined with a subsequent single failure condition 
(referred to as ``latent-plus-one'' conditions).
    The more stringent intent of section 25.901(c) of the Federal 
Aviation Regulations (14 CFR 25.901(c)) (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFar.nsf/FARSBySectLookup/25.901) is 
discussed in further detail in the notice of proposed rulemaking and 
the preamble that were published for Amendment 25-102. The FAA's long-
standing practice in applying the ``no single failure or malfunction'' 
clause of section 25.901(c) of the Federal Aviation Regulations (14 CFR 
25.901(c)) has been to apply that standard to all reasonably 
anticipated flights--not simply to an average flight or an ideal 
flight. As such, we examine all conditions: Flights with reasonably 
anticipated pre-existing failure conditions, flights with inoperative 
equipment allowed for dispatch, and flights in adverse environmental 
conditions or other operational conditions for which the airplane is 
approved. If single failure conditions that jeopardize safe operation 
of the airplane (catastrophic or hazardous conditions) are identified 
as part of this examination, the design is considered to be non-
compliant with section 25.901(c) of the Federal Aviation Regulations 
(14 CFR 25.901(c)).
    Finally, the SFAR 88 AD-decision policy (Policy Memo ANM-100-2003-
112-15) (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/DC94C3A46396950386256D5E006AED11?OpenDocument&Highlight=anm-100-2003-112-15) classifies a ``latent-plus-one'' condition in a high 
flammability fuel tank as an unsafe condition requiring corrective 
action. That policy actually provides some relief from the latent-plus-
one criteria contained in the airworthiness regulations.
    We have not changed this SNPRM regarding this issue.

Request To Withdraw NPRM (77 FR 12506, March 1, 2012): Not Supported by 
Risk Analysis

    Airlines for America (A4A) proposed that we re-evaluate the NPRM 
(77 FR 12506, March 1, 2012) because it is ``not founded on a data-
based risk analysis.'' A4A stated that the FAA determined that an 
unsafe condition exists based only on non-compliance with one SFAR 88 
criterion. A4A noted that the design approval holder, Boeing, has 
performed a numerical probability analysis and has calculated that the 
probability of a fuel tank explosion due to the FQIS issue is 
approximately one event per billion flight hours, with cargo airplanes 
being slightly better due to a lower average tank flammability. A4A 
also stated that existing ignition-prevention ADs have reduced the 
overall risk of an ignition event to a level that questions the need 
for FQIS modification. We infer that the commenter is requesting that 
we withdraw the NPRM.
    We disagree to withdraw the NPRM (77 FR 12506, March 1, 2012). We 
performed a qualitative risk assessment in accordance with our 
published SFAR 88 unsafe condition determination policy based on 
Boeing's submitted SFAR 88 design review, and determined that the FQIS 
design on the Model 757 series airplanes presents an unsafe condition 
and that AD action was warranted under that policy. We also performed a 
data-based numerical risk analysis using data provided by the 
manufacturer, and assessed the risk under the transport airplane unsafe 
condition criteria in the TARAM policy currently used by the FAA. Our 
risk analysis determined that the risk of an explosion event due to an 
FQIS latent-plus-one failure condition is not evenly shared by all 
flights of airplanes of the affected design. Instead, the risk of an 
FQIS-related fuel tank ignition event is largely concentrated on the 
subset of flights that occur with a pre-existing latent failure 
condition and that operate with flammable conditions in the center fuel 
tank. Based on Boeing's data, such flights are reasonably anticipated 
to occur.
    For those flights, the risk exceeds the allowable threshold for 
individual flight safety risk in the TARAM policy. In addition, that 
risk on those flights is due to a single additional failure, which is 
inconsistent with the fail-safe design philosophy; that philosophy is 
fundamental to the excellent safety record of transport airplanes. (See 
FAA Advisory Circular (AC) 25.1309-1A, ``System Design and Analysis,'' 
dated June 21, 1998 (http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2025.1309-1.pdf), for a discussion of the fail-
safe design philosophy.) We would normally classify either of those 
conditions as an unsafe condition. Based on this risk analysis, we have 
determined that the individual flight safety risk due to this issue on 
the worst anticipated flights does not meet the minimum level of safety 
required by the FAA and expected by the public. We have not changed 
this SNPRM regarding this issue.

Request To Withdraw or Delay NPRM (77 FR 12506, March 1, 2012): Need 
Detailed Risk Assessment

    FedEx requested that we revise the NPRM (77 FR 12506, March 1, 
2012) to provide a numerical risk assessment justifying the proposed 
action. UPS made a similar comment. UPS stated that, if the FAA has 
gathered new data since the issuance of the ``Reduction of Fuel Tank 
Flammability in Transport Category Airplanes'' rule (73 FR 42444, July 
21, 2008) (http://www.gpo.gov/fdsys/pkg/FR-2008-07-21/pdf/E8-16084.pdf), referred to as the Fuel Tank Flammability Reduction (FTFR) 
rule, the FTFR working group should be reconvened in order to 
collaborate and discuss the proposed safety risk, assess the risk 
statistically, evaluate solutions and options, and establish accurate 
cost and economic impact for the options. FedEx provided an analysis 
showing that the total risk of a tank explosion due to this issue on 
the fleet of Model 757 cargo airplanes is relatively low. We infer that 
the commenters are requesting that we withdraw or delay the NPRM.

[[Page 9403]]

    We disagree with the request to withdraw the NPRM (77 FR 12506, 
March 1, 2012), pending review of the FAA's numerical risk assessment 
by the ``FTFR working group.'' The Aviation Rulemaking Advisory 
Committee (ARAC) Fuel Tank Harmonization Working Group (FTHWG) was 
tasked to recommend new rulemaking to eliminate or significantly reduce 
the risk of exposure to flammable fuel-air mixtures in fuel tanks. The 
ARAC FTHWG issued its final report in 1998. The subsequent ARAC Fuel 
Tank Inerting Harmonization Working Group (FTIHWG) was tasked to 
provide data needed for the FAA to evaluate the feasibility of 
implementing regulations that would require eliminating or 
significantly reducing the development of flammable vapors in fuel 
tanks on transport-category airplanes. This effort was an extension of 
the previous work performed by the FTHWG. The ARAC FTIHWG issued its 
final report in 2002. The FAA's work in developing the SFAR 88 
corrective action decision policy and in determining specific unsafe 
conditions was outside the scope and charter of these working groups 
that contributed to the FTFR rule (73 FR 42444, July 21, 2008). We 
determined that an unsafe condition exists in accordance with the SFAR 
88 corrective action decision policy and TARAM policy. We have provided 
a summary of our risk assessment as discussed in the responses to 
``Request to Withdraw NPRM (77 FR 12506, March 1, 2012): Unjustified by 
Risk'' and ``Request to Withdraw NPRM (77 FR 12506, March 1, 2012): Not 
Supported by Risk Analysis'' in this SNPRM. As explained previously 
(see ``Request to Withdraw NPRM (77 FR 12506, March 1, 2012): 
Unjustified by Risk'' in this SNPRM), the FAA determined the unsafe 
condition based on the unacceptable risk on anticipated flights with a 
latent FQIS failure and flammable fuel tank conditions, not the total 
fleet risk. We have not changed this SNPRM regarding this issue.

Request To Withdraw NPRM (77 FR 12506, March 1, 2012): No Unsafe 
Condition

    UPS stated that an SFAR 88 working group analyzed potential fuel 
tank ignition sources and that maintenance programs were revised using 
MSG3 methodology to meet the revised criteria in ``14 CFR 25.981(3).'' 
(We assume UPS intended to refer to section 25.981(a)(3) of the Federal 
Aviation Regulations (14 CFR 25.981(a)(3))) (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/73716).) UPS stated that the unsafe 
condition identified in the NPRM is inconsistent with the working group 
analysis and lacks new data or evidence indicating that ``excessive 
flammability or other known unsafe condition exists, or is likely to 
develop.'' Finally, UPS made the following observation about the NPRM:

    The NPRM fails to consider the beneficial effects of the timing 
and effects of the maintenance action in response to a single in-
tank or out-of-tank failure mode, or the beneficial effects of 
previous airworthiness directives and other SFAR 88 related actions 
taken to mitigate the proposed risk and reduce the probability.

    We infer that the commenter is requesting that we withdraw the NPRM 
(77 FR 12506, March 1, 2012). We disagree with the request to withdraw 
the NPRM. The FAA has performed a risk assessment and has determined 
that an unsafe condition does exist, both from a design architectural 
standpoint and a numerical risk standpoint. The basis for that 
determination is discussed in detail in the responses to ``Request to 
Withdraw NPRM (77 FR 12506, March 1, 2012): Unjustified by Risk'' and 
``Request to Withdraw NPRM (77 FR 12506, March 1, 2012): Not Supported 
by Risk Analysis'' in this SNPRM.
    The requirements of section 25.981(a)(3) of the Federal Aviation 
Regulations (14 CFR 25.981(a)(3)) cannot be met with an approved 
maintenance program only. While an appropriate maintenance program is 
required, section 25.981(a)(3) of the Federal Aviation Regulations (14 
CFR 25.981(a)(3)) has the effect of setting minimum requirements for 
the design architecture and the reliability of system elements. The 
Model 757 FQIS as originally designed does not meet all of those 
requirements. Previous AD actions, other than the required maintenance 
program revisions included in AD 2012-12-15, Amendment 39-17095 (77 FR 
42964, July 23, 2012) (which superseded AD 2008-10-11, Amendment 39-
15517 (73 FR 25974, May 8, 2008)), have no effect on the level of 
individual flight risk that has been determined to be an unsafe 
condition. Some of the airworthiness limitations (AWLs) introduced by 
AD 2012-12-15 will reduce the rate of introduction of additional risks 
due to future maintenance errors or modifications compromising required 
design features, but are not expected to prevent all errors. Those AWLs 
do not address problems that may already exist or develop on in-service 
airplanes separate from maintenance activity, and they do not address 
the basic non-compliant aspects of the original FQIS design 
architecture. Those AWLs therefore would not have a significant effect 
on either the number of flights that occur with a latent failure 
condition or the FQIS-related fuel tank explosion risk level on those 
flights estimated in the FAA's risk assessment. We have not changed 
this SNPRM regarding this issue.

Request To Withdraw NPRM (77 FR 12506, March 1, 2012): No Unsafe 
Condition

    Airbus acknowledged that the latent-plus-one scenarios that 
prompted the unsafe condition determination are a technical 
possibility, but stated that the failure combinations that can create 
an ignition source are extremely improbable. Airbus also stated that 
AD-required airworthiness limitations related to FQIS have 
significantly reduced the likelihood of an FQIS-related fuel tank 
ignition event. We infer that Airbus is requesting that we withdraw the 
NPRM (77 FR 12506, March 1, 2012) based on Airbus's contention that no 
unsafe condition exists.
    We agree to clarify the likelihood that the unsafe condition could 
occur. The FAA's unsafe condition determination was not based on an 
assessment of average risk. We agree that the average risk of a fuel 
tank explosion on the Model 757 is likely to be lower than the 
numerical guidance for ``extremely improbable'' of 1.0x10E-9 per flight 
hour. We also agree that the average risk was likely reduced by AD-
required airworthiness limitations that specify extra checks after in-
tank work, and adequate separation of newly installed out-of-tank 
wiring from FQIS wiring.
    As discussed in ``Request to Withdraw NPRM (77 FR 12506, March 1, 
2012): Unjustified by Risk'' in this SNPRM, however, the FAA's unsafe 
condition determination was driven by the identification of an 
unacceptable level of individual risk that exists on flights that are 
anticipated to occur with a pre-existing latent in-tank failure 
condition and with a flammable center fuel tank. In the remaining life 
of the affected airplanes, a significant number of such flights are 
reasonably anticipated to occur--even with the improvements expected 
under the AWLs required by AD 2012-12-15, Amendment 39-17095 (77 FR 
42964, July 23, 2012). For those flights, a fuel tank explosion can be 
caused by an additional single wiring failure. In addition, the 
manufacturer's estimated probability of such a failure (the additional 
single wiring failure) significantly exceeds the FAA's unsafe condition 
numerical threshold for individual flight risk. The probability of

[[Page 9404]]

a fuel tank explosion on those flights is not reduced by the existence 
of the above-mentioned AWLs. The AWL that requires extra checks after 
in-tank work has been done has the potential to reduce the number of 
flights with a pre-existing in-tank failure condition. The AWL that 
requires newly installed wiring to meet separation standards should 
prevent a significant increase in the risk on those flights that would 
have resulted from the installation of additional, inadequately 
separated wiring.
    We have not changed this SNPRM regarding this issue.

Request To Withdraw NPRM (77 FR 12506, March 1, 2012) Based on Similar 
Rulemaking for Cargo Airplanes

    ASTAR Air Cargo (ASTAR) requested that we withdraw the NPRM (77 FR 
12506, March 1, 2012). In support of its request, ASTAR cited the TWA 
Flight 800 accident investigation and its finding that the most 
probable cause of the accident was a fuel tank explosion due to a 
latent-plus-one failure of the FQIS. ASTAR stated that the FAA had 
proposed the FTFR rule (73 FR 42444, July 21, 2008) to mitigate the 
risk of fuel tank explosions, and that cargo airplanes had been 
exempted from that requirement based on a cost-benefit analysis. ASTAR 
argued that, because the basis for exclusion of all cargo aircraft from 
the FTFR rule has not changed, all cargo aircraft should be exempt from 
any corrective action for the FQIS latent-plus-one issues, and the NPRM 
(77 FR 12506, March 1, 2012) should be withdrawn.
    We disagree with the request. We have determined that an unsafe 
condition requiring corrective action exists in the Model 757 FQIS. The 
FTFR rule (73 FR 42444, July 21, 2008) was proposed not because of FQIS 
issues specifically, but because of the history of fuel tank explosions 
in the transport airplane fleet due to various causes, and an 
acknowledgement that industry and the FAA may not be able to anticipate 
and prevent all of the fuel tank ignition sources that may arise due to 
design and maintenance issues in the life of a fleet of airplanes.
    The intent of the FTFR rule (73 FR 42444, July 21, 2008) was to 
reduce the overall exposure to flammable fuel tank conditions in the 
fleet by approximately one order of magnitude with the expectation that 
this would have a significant impact on the rate of fuel tank 
explosions in the future due to unanticipated causes. In promulgating 
this improvement in the safety standards, the FAA acknowledged that 
installation of FRM or ignition mitigation means on a given airplane in 
accordance with the FTFR rule would be sufficient to address the FQIS 
latent-plus-one unsafe condition. The FTFR rule was not intended to 
prevent the FAA from addressing that unsafe condition on airplanes that 
would not be affected by the FTFR rule. This was clearly stated in the 
preamble to the FTFR rule. We have not changed this SNPRM regarding 
this issue.

Request To Withdraw NPRM (77 FR 12506, March 1, 2012): Underestimated 
Economic Impact

    Several commenters requested that we withdraw the NPRM (77 FR 
12506, March 1, 2012) because the FAA's cost estimate was too low. A4A 
estimated that the costs associated with the NPRM would be up to 3 
times the $100,000 to $200,000 estimated by the FAA, and would be 
comparable with the cost of Boeing's NGS installation. Goodrich pointed 
out that any redesigned FQIS would likely be subject to the current 
requirements of section 25.981 of the Federal Aviation Regulations (14 
CFR 25.981), resulting in higher costs than estimated by the FAA. A4A 
speculated that these higher costs were the reason the NGS was 
acknowledged as a method of compliance in the NPRM. A4A and UPS stated 
that the FAA appears to be using the NPRM as a method to require the 
installation of Boeing's NGS (or equivalent actions) on airplanes that 
were not included in the applicability of the FTFR rule (73 FR 42444, 
July 21, 2008) based on a cost-benefit analysis.
    Although we disagree to withdraw the NPRM, we agree with some of 
the commenters' assertions. We agree that our original cost estimate 
was low. We agree to adjust the cost estimate, based on the information 
provided by the commenters, as discussed below under ``Request to 
Revise Cost Estimate Based on New Data.'' Our original estimate was 
based on information provided previously by manufacturers of original 
equipment FQIS, retrofit FQIS, and both original equipment and 
aftermarket transient suppression and isolation devices. Our current 
estimate has been increased to reflect the written comments from and 
further discussions with Boeing and Goodrich. There is no change to our 
determination that an unsafe condition exists. We are therefore 
proceeding with this AD action based on the identified corrective 
actions that will address the unsafe condition.
    We disagree with the characterization that we are using the AD 
process to require an FRM to be installed on airplanes that were 
excluded from the FTFR rule (73 FR 42444, July 21, 2008) because 
inclusion could not be justified in a cost-benefit analysis. The FTFR 
rule was intended to enhance the airworthiness standards in a manner 
that would increase the level of safety for affected airplanes over 
that ensured by the existing regulations. That enhancement was expected 
to result from an increased level of protection from ignition sources 
that had not been identified by manufacturers in their safety analyses. 
That enhancement of the airworthiness standards was required to be 
justified by a cost-benefit analysis. Cargo airplanes were excluded 
because the FTFR rule safety enhancement could not be justified for 
those airplanes from a cost-benefit standpoint.
    This SNPRM would not require a safety enhancement over the level of 
safety required by previous standards. Instead, this SNPRM addresses an 
unsafe condition that was identified from the manufacturer's SFAR 88 
safety analysis using the FAA's published corrective action decision 
criteria for SFAR 88 identified design issues (see section 25.981(a)(3) 
of the Federal Aviation Regulations (14 CFR 25.981(a)(3) (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/73716). We deferred taking action on 
this unsafe condition until after the FTFR rulemaking activity because 
the installation of an FRM would sufficiently address the FQIS latent-
plus-one unsafe condition. Now that the FTFR rulemaking process is 
complete, we are resuming our activity to address these unsafe 
conditions via AD actions. The Boeing NGS has been acknowledged as a 
method of compliance in this SNPRM because the Boeing NGS is an 
available design that the FAA knows would address the unsafe condition. 
No additional change was made to this SNPRM as a result of this 
comment.

Request To Withdraw NPRM (77 FR 12506, March 1, 2012) Due to Its Hidden 
Effects

    A4A requested that we withdraw the NPRM (77 FR 12506, March 1, 
2012) because of certain hidden effects that may not have been 
anticipated by the FAA. A4A pointed out that some operators are already 
anticipating difficulty in meeting the deadlines for compliance with 
the FTFR rule (73 FR 42444, July 21, 2008). Based on A4A's assumption 
that airlines would comply with the NPRM by incorporating Boeing's 
current NGS design, A4A expressed concern that using Boeing's NGS for 
these additional airplanes would potentially exceed the rate at

[[Page 9405]]

which industry can modify the fleet affected by the planned ADs and the 
FTFR rule. A4A also noted that the compliance time for the NPRM would 
overlap the compliance period for the FTFR rule.
    While we disagree with the request to withdraw the NPRM, we agree 
with some of the assertions made by the commenter. We agree with the 
concern that this AD action has the potential to further burden the 
operators and modifiers that are working to meet the FRM operating rule 
deadlines, because some additional airplanes are likely to be modified 
by installing FRM such as Boeing's NGS. But since we issued the NPRM 
(77 FR 12506, March 1, 2012), two factors have changed that reduce 
A4A's concern. First, we have identified a less costly option for cargo 
airplanes, which most cargo operators are expected to prefer over 
installation of FRM. This is expected to result in significantly fewer 
airplanes competing for FRM modification resources. Second, this AD 
action has been delayed due to numerous factors, including the number 
of comments, the development of a different corrective action option, 
and the resultant need to extend the comment period to allow the public 
the chance to comment on these proposed changes.
    Also, as discussed below under ``Request to Extend Compliance Time 
Pending Issuance of Service Information,'' we have extended the 
proposed compliance time by 12 months. These delays and changes will 
result in the AD compliance deadline being at least 3 years beyond the 
final compliance deadline of the FTFR rule (73 FR 42444, July 21, 
2008). Similar planned ADs for other models have been similarly 
delayed. We have determined that the industry modification capacity 
will be sufficient to support the modification of the expected 
additional airplanes receiving FRM within the new proposed compliance 
time. We have not changed this SNPRM further regarding this issue.

Request To Withdraw NPRM (77 FR 12506, March 1, 2012): Potential 
Significant Rule

    A4A stated that the combined costs of the NPRM (77 FR 12506, March 
1, 2012) and other anticipated ADs for U.S. airplane models with an 
FQIS latent-plus-one issue would exceed $177 million and would require 
a cost-benefit analysis. We infer that the commenter is requesting we 
withdraw the NPRM (77 FR 12506, March 1, 2012) on the basis that the 
planned ADs for various models, if combined, would qualify as a 
significant rule that would require a cost-benefit analysis.
    We disagree with the request. First, in assessing whether an AD is 
a significant rule in accordance with FAA policy, we do not combine the 
cost of multiple planned ADs for different airplanes, even when the 
design issues and unsafe conditions addressed are similar. Second, the 
changes discussed previously in this SNPRM will significantly reduce 
the cost impact. We have made no further changes to this SNPRM 
regarding this issue.

Request To Withdraw NPRM (77 FR 12506, March 1, 2012): Inadequate 
Notice to Public

    A4A recommended that we provide information on any other designs 
that have been reviewed under SFAR 88, and provide industry with 
information regarding their planned disposition. A4A asserted that, 
during the FTFR rulemaking activity, we did not provide notice to the 
industry that we still intended to address the FQIS issues identified 
via SFAR 88. We infer that A4A is requesting that we withdraw the NPRM 
(77 FR 12506, March 1, 2012) based on inadequate notice to the public 
and the chance to comment on the proposal. The commenter stated that 
the preamble of the FTFR rule (73 FR 42444, July 21, 2008) was unclear 
regarding whether AD actions would be taken to address the FQIS issues 
on airplanes that were not required to incorporate FRM.
    We disagree with the request to withdraw the NPRM (77 FR 12506, 
March 1, 2012). We determined that an unsafe condition exists. FTFR 
rulemaking was done because the FAA recognized the benefit for the 
specific design changes involving incorporation of FRM required by the 
FTFR rule (73 FR 42444, July 21, 2008) to enhance fuel tank safety. 
Because the FTFR final rule requires action on only a subset of the 
airplanes that have the FQIS unsafe condition, we are taking action to 
address the remaining airplanes that will continue to have the unsafe 
condition if no further corrective action is taken.
    The commenter has taken the statement from the FTFR preamble out of 
context. In fact, the paragraph from which the commenter quoted 
specifically states that the FAA expected to take AD action to address 
FQIS issues identified through SFAR 88 analyses. The paragraph simply 
states that the proposed FRM has the potential to reduce the industry 
cost associated with those expected ADs because the installation of an 
FRM likely would eliminate the need for action to further address the 
FQIS issue with AD actions. The purpose of that statement was to note 
that there would be some cost savings to industry resulting from the 
elimination of other actions required to address an unsafe condition 
for the airplanes affected by the proposed rules, and to point out that 
the FAA did not take credit for those potential cost reductions in 
assessing the cost of the FTFR rule (73 FR 42444, July 21, 2008) 
because the costs were not well understood at the time. That statement 
was not a commitment by the FAA to reverse its intentions to address an 
identified unsafe condition on the airplanes that are not required to 
incorporate FRM. We have not changed this SNPRM regarding this issue.

Request for Cost-Benefit Analysis

    Boeing, FedEx, Airbus, ASTAR Air Cargo, and A4A requested that we 
perform a cost-benefit analysis for the NPRM (77 FR 12506, March 1, 
2012) and publish the results. Airbus stated that its own cost 
estimates exceed those used by the FAA for the FTFR rule (73 FR 42444, 
July 21, 2008) cost-benefit analysis that ended up excluding cargo 
airplanes. A4A and ASTAR Air Cargo requested that the NPRM be withdrawn 
until a cost-benefit analysis is performed. The commenters suggested 
that a cost-benefit analysis would show that the NPRM cannot be 
justified because the costs of the proposed actions would exceed the 
monetary value of the AD's safety benefits. The commenters cited the 
cost-benefit analysis that was performed to justify the FTFR rule, and 
pointed out that a requirement for FRM could not be justified for the 
airplanes that would be affected by the proposed AD.
    We infer that, pending a full cost-benefit analysis, these 
commenters are requesting that we either withdraw the NPRM or delay 
this action further until a cost-benefit analysis demonstrates that an 
AD is justified in this case. We disagree. The FAA's process and legal 
obligations for introducing new airworthiness standards are different 
from those for initiating an AD to address an unsafe condition in an 
existing product. In addition, the commenters' assertions were based on 
the assumption that the only design solution that would be made 
available to address the solution would be an FRM, or another solution 
of similarly high cost.
    When we propose a new airworthiness standard, as in the case of the 
FTFR rule (73 FR 42444, July 21, 2008), we are required to perform a 
cost-versus-benefit comparison to justify the application of the new 
standard. The

[[Page 9406]]

decision in that rulemaking action--to not require FRM installation on 
cargo airplanes--was based in significant part on cost estimates that 
industry provided to show that AD-required FQIS design changes would be 
far less costly than installing FRM on cargo airplanes. We specifically 
considered the option to not require retrofit of cargo airplanes with 
FRM because of the expectation that alternative design solutions to 
address the specific, known unsafe condition of FQIS latent-plus-one 
vulnerability would still be required through AD actions. For this AD 
action, however, industry submitted written comments and made verbal 
statements that the cost of an FQIS design solution would be comparable 
to, and possibly greater than, the cost of its FRM modification.
    In general, a full cost-benefit analysis is rarely required for an 
AD. As a matter of regulation, in order to be airworthy, an aircraft 
must conform to its type design and be in a condition for safe 
operation. The type design is approved only after the FAA makes a 
determination that the design complies with all applicable 
airworthiness requirements. In adopting and maintaining those 
requirements, the FAA has already made the determination that those 
requirements establish a level of safety that is cost beneficial. A 
finding of an unsafe condition that warrants AD action means that this 
cost-beneficial level of safety is no longer being achieved, and the 
required AD actions are necessary to restore that level of safety. 
Because this level of safety has already been determined to be cost 
beneficial and does not add an additional regulatory requirement, a 
full cost-benefit analysis for each AD would be redundant and 
unnecessary.
    We have not changed this SNPRM regarding this issue.

Request To Revise Applicability Statement To Clarify the Intent of the 
Rule for Non-U.S.-Registered Airplanes

    The European Aviation Safety Agency (EASA), the Technical Agent for 
the Member States of the European Community, requested that we revise 
the proposed applicability. Specifically, EASA requested that we add 
Model 757 airplanes that did not have FRM installed in production. EASA 
further requested that we exclude airplanes equipped with FRM that meet 
the FAA's FTFR rule (73 FR 42444, July 21, 2008). EASA stated that it 
has not issued an operating regulation corresponding to the FAA's 
requirements for retrofitting FRM in the FTFR rule. EASA noted that, at 
least for European operators, the unsafe condition would not be 
required to be addressed for airplanes that would have been subject to 
the FTFR rule in the U.S., and suggested that EASA might have to issue 
an AD (instead of adopting the FAA AD), with similar technical content, 
but extending the applicability to the entire Model 757 fleet in 
Europe.
    We agree to revise the applicability. EASA is correct that the 
unsafe condition potentially affects all Model 757 airplanes, whereas 
the applicability statement in the NPRM (77 FR 12506, March 1, 2012) 
could be interpreted as not covering airplanes in passenger service 
that are not operated under parts 121, 125, or 129 of the Federal 
Aviation Regulations (14 CFR part 121, 125, or 129). The EASA comment 
makes it apparent that the proposed applicability statement may be 
unclear to some operators and regulatory authorities. While the 
applicability statement in the NPRM is technically correct (e.g., an 
EASA operator is not operating under those FAA operating rules and 
therefore would have been subject to the AD), we now agree that there 
is a potential for confusion that can be eliminated by more directly 
stating the requirement and applicability in a manner similar to that 
proposed by EASA in their comment. We have changed the applicability in 
this SNPRM to all Model 757 airplanes except for airplanes equipped 
with an FRM approved by the FAA as compliant with the FTFR requirements 
of section 26.33(c)(1) of the Federal Aviation Regulations (14 CFR 
26.33(c)(1)), as discussed below. As with any required equipment, the 
FRM must be operational with the exception of any relief granted under 
master minimum equipment list (MMEL) provisions.
    With the clarification in paragraph (c), ``Applicability,'' of this 
SNPRM, we have determined that paragraph (h), ``Optional Installation 
of Flammability Reduction Means,'' of the NPRM would be superfluous and 
is no longer necessary. Paragraph (c) of this supplemental NPRM, as 
revised, would not apply to airplanes equipped with FRM.

Requests To Withdraw NPRM (77 FR 12506, March 1, 2012) Based on 
Applicability

    Boeing and ASTAR Air Cargo requested that we withraw the NPRM (77 
FR 12506, March 1, 2012) because cargo airplanes on average have a 
lower flammability exposure due to a larger portion of night operations 
(with resultant cooler outside air temperatures) and a lower rate of 
utilization of the cabin air conditioning system on the ground. Boeing 
stated that operation of the air conditioning system on the ground 
significantly contributes to the heating of the center fuel tank. 
Boeing's analysis estimated a fleet average flammability for the center 
fuel tanks of the cargo airplane fleet of 50 percent of the level for 
the passenger fleet. Boeing also noted that cargo airplanes generally 
accumulate flight hours at a lower rate than passenger airplanes.
    We disagree with the request to withdraw the NPRM (77 FR 12506, 
March 1, 2012).
    We acknowledge that the increased night operation and reduced use 
of the air conditioning system on the ground reduce the average 
flammability exposure for the fleet of cargo airplanes relative to the 
fleet of passenger airplanes. That reduction in fleet average 
flammability, however, is not sufficient to allow the center fuel tanks 
on those airplanes to be classified as low flammability fuel tanks. The 
FAA's determination that an unsafe condition exists for the cargo 
airplanes as well as passenger airplanes was driven by the FAA's 
individual risk safety decision criteria rather than an average risk or 
fleet risk criterion. There is no difference in the individual flight 
risk on the worst anticipated flights between passenger airplanes and 
cargo airplanes due to this issue. The worst anticipated flights in 
either case involve a pre-existing latent in-tank failure and operation 
with flammable conditions in the center fuel tank. Flights with that 
combination of conditions are anticipated to occur in both the 
passenger fleets and cargo fleets (although at a somewhat lower 
relative rate on cargo airplanes, for the reasons cited by the 
commenters).
    For those flights, a fuel tank explosion could occur due to a 
single failure in the airplane wiring or the FQIS processor that 
conducts a high level of electrical energy onto circuits that enter the 
fuel tank. As discussed previously in the response to ``Request to 
Withdraw NPRM (77 FR 12506, March 1, 2012): Unjustified by Risk,'' this 
is not consistent with the FAA's fail-safe design philosophy for 
transport airplanes. In addition, the numerical probability of the 
single failure as estimated by the manufacturer and the FAA 
significantly exceeds the unsafe condition threshold for individual 
flight risk in the FAA's TARAM) Policy Statement PS-ANM-25-05 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/4E5AE8707164674A862579510061F96B?OpenDocument&Highlight=ps-anm-25-05). 
We have therefore determined that an unsafe condition does exist on 
cargo

[[Page 9407]]

airplanes even in consideration of the lower fleet exposure factors 
cited by the commenters.
    While we have determined that this unsafe condition requires 
corrective action, we have identified additional corrective action 
options that we expect will be significantly less costly to incorporate 
than the originally proposed requirement. We have determined that this 
additional corrective action option is not suitable for passenger 
airplanes because it does not provide a sufficient level of risk 
reduction for passenger operations. The FAA normally does not 
differentiate between the safety requirements or corrective action 
requirements for cargo airplanes and passenger airplanes. However, 
after reviewing all of the comments on the estimated high cost of the 
corrective action and the uncertainty in those estimates, we examined 
other options for less costly risk reduction on cargo airplanes. We 
identified an option that provides significant risk reduction at a per-
airplane cost that is estimated to be less than one-quarter of the cost 
of the original proposal (77 FR 12506, March 1, 2012). The amount of 
risk reduction from this option is not at this time considered to be 
adequate to address the unsafe condition for passenger airplanes.
    In this case, the FAA is proposing to accept a higher level of 
individual flight risk exposure for cargo flights that are not fail-
safe due to the absence of passengers and the resulting significant 
reduction in occupant exposure on a cargo airplane versus a passenger 
airplane, and due to relatively low estimated individual flight risk 
that would exist on a cargo airplane after the corrective actions are 
taken. The FAA has allowed a higher risk level to exist on cargo 
airplanes due to other issues, and applies a slightly less stringent 
numerical fleet risk threshold standard for unsafe conditions in the 
published TARAM policy. Because this is an unusual determination, we 
have reopened the comment period to give affected operators, pilots, 
and the public the opportunity to comment on this proposal.
    We expect that the optional wire separation design change to 
support compliance with the proposed AD for cargo airplanes will 
involve the manufacturer or any other modifier petitioning for a 
partial exemption from the ``latent-plus-one'' requirements of sections 
25.901(c) and 25.981(a)(3) of the Federal Aviation Regulations (14 CFR 
25.901(c) and 14 CFR 25.981(a)(3)). We have informed the manufacturer 
that we are open to granting such an exemption, and they indicated 
their willingness to make such a petition.
    We have added new paragraph (h) in this SNPRM to allow repetitive 
FQIS built-in test equipment (BITE) checks and modification of the 
airplane by separating FQIS wiring from other aircraft wiring that is 
not intrinsically safe (in a manner acceptable to the FAA) as an 
additional option for airplanes used exclusively for cargo operations. 
We have redesignated subsequent paragraphs of this SNPRM accordingly.

Request To Change Applicability To Address Unsafe Condition on 
Airplanes With FRM

    National Air Traffic Controllers Association (NATCA) requested that 
we revise the NPRM (77 FR 12506, March 1, 2012) to include airplanes on 
which FRMs were incorporated either voluntarily or to comply with the 
FTFR rule (73 FR 42444, July 21, 2008). NATCA noted that the 
introduction of FRM on such airplanes only reduces the fraction of time 
the airplane is operated with flammable conditions in its fuel tanks, 
but does not eliminate flammable operation. NATCA further noted that 
FAA operating rules allow limited operation of the airplane with the 
FRM inoperative. NATCA added that the likelihood of a fuel tank 
explosion during operation with flammable tanks is similar regardless 
of whether an FRM is installed.
    We disagree with the request. We have developed and published 
policy for determination of unsafe conditions and the need for 
corrective actions during the evaluation of SFAR 88 fuel tank safety 
review findings. The decision to allow FRM as an acceptable mitigating 
action for the identified unsafe condition is consistent with that 
policy. We acknowledge NATCA's point that, if no actions are taken on 
an airplane to correct the FQIS latent-plus-one issue other than 
installation of an FRM, flights on that airplane where FRM is 
inoperative or ineffective would have the same risk of a fuel tank 
explosion due to the FQIS latent-plus-one issue as flights on an 
airplane with no FRM installed. However, the published unsafe condition 
criteria (section 25.981(a)(3) of the Federal Aviation Regulations (14 
CFR 25.981(a)(3)) (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/73716) 
differentiate between low- and high-flammability fuel tanks, with a 
higher level of conservatism applied to high-flammability tanks.
    The criteria recognize that low-flammability tanks are still 
flammable for a portion of their operating time, and the criteria 
include ignition prevention thresholds commensurate with that level of 
flammability. The regulatory performance standard for FRMs is 
equivalent to the flammability of a conventional aluminum wing tank, 
which is the benchmark for the definition of a low-flammability tank. 
We have therefore determined that it is appropriate to treat ignition 
sources in center fuel tanks with compliant FRMs the same way they 
would be treated for a tank that has inherent low flammability. Because 
the FQIS latent-plus-one vulnerability for Model 757 airplanes was 
classified as a theoretical vulnerability and not as a condition known 
to have occurred, the SFAR 88 corrective action policy does not require 
corrective action for that condition in low-flammability fuel tanks. 
The installation of an FRM causes the center fuel tank to meet the 
criteria for classification as a low-flammablity fuel tank, and 
therefore FRM installation was considered to be acceptable mitigating 
action. We have not changed this SNPRM regarding this issue.

Request To Remove Requirement for Goodrich FQIS

    Goodrich stated that its FQIS fuel height and dielectric sensor 
interface circuitry presently meets the energy, voltage, and current 
limits specified in FAA AC 25.981-1C, ``Fuel Tank Ignition Source 
Prevention Guidelines,'' dated September 19, 2008 (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/73716). Goodrich stated that the system 
design would require multiple serial failures to enable a fault to 
propagate to the tank, resulting in the combination of those failures 
being extremely improbable on average. Goodrich added that the system 
built-in test detects open circuits and short circuits in the sensors 
and aircraft wiring, including shorts to structure. Goodrich stated 
that there have been no failures in service in which the Goodrich FQIS 
exposed the fuel tank to an unsafe condition. Goodrich asked whether 
the actual system operation and service life have been considered in 
the evaluation of the probability of an unsafe condition and the 
mitigation provided by the present Goodrich FQIS.
    We infer that the commenter is requesting that we revise the NPRM 
(77 FR 12506, March 1, 2012) to eliminate any requirement for 
corrective action for airplanes equipped with a Goodrich FQIS. We 
partially agree. The Goodrich system is recognized as having 
significant improvements relative to the

[[Page 9408]]

original 757 system developed by another manufacturer. We recognize 
that the Goodrich FQIS has the ability to identify a significant 
portion of the potential latent in-tank failure conditions that can 
occur inside the fuel tanks. Those conditions, however, are detected 
and corrected only when the built-in test capability is activated 
during maintenance. Currently, activating the built-in test features is 
required only when troubleshooting an FQIS problem that has become 
apparent to flight or maintenance crew. This still potentially leaves 
significant latency periods for those failures.
    We have agreed that the Goodrich processor has sufficient circuit 
isolation such that the processor itself is not expected to create hot 
short conditions in tank circuits, and is not expected to pass energy 
from non-tank-side low-voltage hot shorts onto tank-side circuits. 
There remains, however, a significant potential for a single failure 
causing a hot short onto tank-side circuits, or a single failure 
causing a high-voltage hot short onto non-tank-side circuits to cause 
non-intrinsically safe energy, voltage, or current levels to be 
conducted into the fuel tanks. The latent-plus-one concern therefore 
still exists even with the additional detection capabilities that exist 
in the Goodrich FQIS. We have determined this concern requires 
corrective action in accordance with the SFAR 88 corrective action 
decision policy discussed previously. We disagree with the request to 
revise this SNPRM to eliminate any requirement for corrective action 
for airplanes equipped with a Goodrich FQIS because we have determined 
that an unsafe condition requiring corrective action exists on the 
Goodrich FQIS-equipped airplanes even after considering the differences 
between the Goodrich FQIS and the original 757 system developed by 
another manufacturer. We have not changed this SNPRM regarding this 
issue.

Request To Clarify Affected Tanks

    FedEx requested that we revise the NPRM (77 FR 12506, March 1, 
2012) to clarify that only the center fuel tank is affected. FedEx 
stated that the proposed wording could be interpreted as applying to 
all tanks.
    We agree to clarify the intent of this SNPRM. The FQIS wiring and 
related system components are to be modified to the extent necessary to 
prevent the development of an ignition source in the center fuel tank 
due to FQIS failure conditions. If modification of wing tank-related 
components is necessary to prevent an ignition source in the center 
fuel tank (for example, because of common wiring between the tanks), 
then that modification would be required. Paragraph (g) of this SNPRM 
already states this (``modify the FQIS wiring or fuel tank systems to 
prevent development of an ignition source inside the center fuel 
tank''). A change to this SNPRM itself therefore is not necessary.

Request To Revise Proposed AD Requirements To Apply to All Fuel Tanks

    NATCA noted that action similar to the proposed requirements of the 
NPRM (77 FR 12506, March 1, 2012) was required for all fuel tanks on 
early Model 747 and 737 airplanes via AD 98-20-40, Amendment 39-10808 
(63 FR 52147, September 30, 1998); and AD 99-03-04, Amendment 39-11018 
(64 FR 4959, February 2, 1999). The commenter also noted that the FAA's 
published SFAR 88 unsafe condition criteria (section 25.981(a)(3) of 
the Federal Aviation Regulations (14 CFR 25.981(a)(3)) (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/73716)) require corrective action for 
``known latent-plus-one conditions'' in both low- and high-flammability 
tanks.
    We infer the commenter is requesting that we revise the proposed 
actions of the NPRM (77 FR 12506, March 1, 2012) to apply to all fuel 
tanks. We disagree. NATCA's interpretation of the word ``known'' 
appears to be different from that intended by the FAA when the SFAR 88 
decision criteria were developed and implemented. For low-flammability 
fuel tanks, the FAA has proposed that corrective action for ``latent-
plus-one'' issues be required only in cases where the particular 
latent-plus-one scenario is known to have occurred on that particular 
design. Where relevant design details are significantly different, a 
condition that has occurred with one design is not considered to be a 
``known'' latent-plus-one condition on another design simply because 
the same architectural vulnerability theoretically exists.
    In the case of AD 98-20-40, Amendment 39-10808 (63 FR 52147, 
September 30, 1998); and AD 99-03-04, Amendment 39-11018 (64 FR 4959, 
February 2, 1999); we required corrective action for all fuel tanks 
because the details of those designs were identical or very similar to 
the details of the design that were considered to be the most likely 
cause of the 1996 Model 747-100 accident. The actions of AD 98-20-40 
and AD 99-03-04 are consistent with the intent of the later-developed 
SFAR 88 unsafe condition criteria. We have not changed this SNPRM 
regarding this issue.

Request for Specific Corrective Action

    EASA noted that the NPRM (77 FR 12506, March 1, 2012) did not cite 
service information for a specific design solution other than 
acknowledging FRM as an acceptable method of compliance. We infer that 
EASA is requesting that the NPRM propose to require a specific 
corrective action for the unsafe condition. EASA pointed out that, 
under its regulations and policies, EASA issues ADs based on specific 
solutions provided by the responsible manufacturer. EASA stated that, 
in the absence of a specific solution, EASA will not be in a position 
to simply adopt the FAA AD, and may need to develop its own AD or find 
another solution.
    We disagree with the request to require a specific corrective 
action in this SNPRM. In this case, the manufacturer has not provided a 
corrective action specific to FQIS in time to support the NPRM, noting 
that they have provided service instructions to install FRM that the 
FAA has defined as one method of compliance within the NPRM (77 FR 
12506, March 1, 2012). While the FAA has the authority to compel the 
manufacturer to provide a solution specifically providing FQIS 
protection, in this case the FAA decided to seek public comment on the 
NPRM (77 FR 12506, March 1, 2012) before deciding whether to take that 
action. The FAA already requires the vast majority of passenger 
airplanes registered in the U.S. to be equipped with FRM, and since we 
defined incorporation of FRM as one method of compliance within the 
NPRM (77 FR 12506, March 1, 2012), and because Boeing and Goodrich 
provided information to show that a specific FQIS protection solution 
would have a per-airplane cost similar to that of Boeing's FRM design 
solution, we have determined there is no practical reason to require 
the manufacturer to provide a corrective action specific to FQIS for 
passenger airplanes. Consideration of the many comments on the NPRM (77 
FR 12506, March 1, 2012) has resulted in a revision of the FAA's 
approach for cargo airplanes, leading to a significantly different 
proposed AD. At this point we do expect the manufacturer to provide 
service information for the proposed optional solution for cargo 
airplanes. We have, however, decided not to further delay action on 
this issue by waiting for that service information. The service 
information is expected to be released shortly after the issuance of a 
final rule.

[[Page 9409]]

No change to this SNPRM is necessary for this issue. If service 
information becomes available before the final rule is issued, we might 
consider incorporating it into the AD.

Request for Information on Modifications

    Icelandair requested more detailed information on the specific 
modifications that would need to be performed to comply with the 
proposed requirements specified in the NPRM (77 FR 12506, March 1, 
2012), and asked if a related service bulletin was available.
    Service information is available for incorporation of FRM approved 
by the FAA as compliant with the FTFR rule (73 FR 42444, July 21, 2008) 
requirements of section 26.33(c)(1) of the Federal Aviation Regulations 
(14 CFR 26.33(c)(1)).
    As stated previously, we have revised the NPRM (77 FR 12506, March 
1, 2012) to provide more specific information about a less costly 
optional modification for cargo airplanes. Service information related 
to this modification is not currently available. We have not changed 
this SNPRM further regarding this issue.

Request for Optional Modification

    Goodrich requested that we revise the NPRM (77 FR 12506, March 1, 
2012) to require or allow a modification to separate and shield the 
FQIS tank-side circuits from other wiring as corrective action for the 
identified unsafe condition. Goodrich referred to its discussion 
regarding the capability of the Goodrich FQIS processor to isolate the 
tank-side circuits from the non-tank-side circuits.
    We partially agree with the request. We considered that method of 
compliance and determined that the benefit from that corrective action 
would be sufficient for cargo airplanes when combined with regular FQIS 
checks using the previously mentioned built-in test capability. We 
disagree with allowing the proposed alternative for passenger airplanes 
that are not equipped with FRM because the level of risk reduction 
achieved from that alternative corrective action would not provide a 
sufficient risk reduction for those airplanes. Even when the built-in 
test capability is periodically exercised, there will still be a 
significant latency period for some in-tank failures. The risk on the 
flights where those failures exist and where flammable conditions exist 
in the fuel tank is considered to be excessive for passenger airplanes, 
because it results from a single additional failure (those flights 
would not be fail-safe). Even if it did not result from an additional 
single failure, it would still exceed the TARAM-allowable risk level 
for individual flight risk. This determination is consistent with the 
SFAR 88 corrective action decision policy and TARAM policy. As 
discussed previously, we have added new paragraph (h) in this SNPRM to 
allow the option of a periodic BITE check and partial wire separation 
for cargo airplanes.

Request for Repetitive Inspections or Replacement

    Oy Air Finland Ltd. stated that wires within the fuel tank must 
remain in an undamaged condition and therefore requested that we revise 
the NPRM (77 FR 12506, March 1, 2012) to specify their repetitive 
inspection or replacement. The commenter provided no justification.
    We disagree with including specific requirements to periodically 
inspect or replace the wiring within the fuel tanks because 
airworthiness limitations and existing maintenance practices are 
already in place to monitor the condition of in-tank wiring. This SNPRM 
would require installation of flammability reduction means or a 
combination of periodic system checks (which would detect many types of 
wiring defects or damage) and wire separation improvements, either of 
which would significantly reduce the probability of a fuel tank 
explosion on a given airplane flight to an acceptable level. We have 
not changed this SNPRM regarding this issue.

Request To Compel Issuance of Service Information

    NATCA requested that we enforce sections 21.99 and 183.63(d) of the 
Federal Aviation Regulations (14 CFR 21.99 and 183.63(d)) and SFAR 88, 
Amendment 21-78, and subsequent Amendments 21-82 and 21-83) (http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgFAR.nsf/0/EEFB3F94451DC06286256C93004F5E07?OpenDocument) to obtain necessary 
service information from design approval holders. NATCA noted that EASA 
cannot ``issue ADs'' (that is, EASA may not be able to adopt the FAA AD 
per se) if specific service information is not identified. NATCA 
expressed concern that other civil aviation authorities may take a 
similar position.
    We partially agree with the request. We agree that the cited 
regulations are relevant in setting requirements for action by design 
approval holders when we have identified an unsafe condition. We also 
recognize that issuance of an AD without service information creates 
significant issues for regulatory agencies and for operators that must 
comply with the AD. This SNPRM, however, is not the appropriate forum 
to discuss potential enforcement action. We have not changed this SNPRM 
regarding this issue.

Boeing's Planned Service Information

    Boeing stated that it will offer only the Boeing FRM as a solution, 
if the AD is issued as proposed. Boeing added that it does not develop 
detailed cost estimates for design changes they do not intend to 
provide. Further, Boeing stated that it does not advocate FRM 
installation on airplanes for which FRM is not required under the FTFR 
rule (``Reduction of Fuel Tank Flammability in Transport Category 
Airplanes'' (73 FR 42444, July 21, 2008)). Boeing proposed no change to 
the NPRM (77 FR 12506, March 1, 2012). Boeing noted that a requirement 
to install an FRM on the affected airplanes could not be justified in 
the cost-versus-benefit analysis performed for the new FTFR rule, and 
therefore cannot be justified to address the unsafe condition 
identified by the FAA.
    We have provided the basis for this SNPRM in response to ``Request 
for Cost-Benefit Analysis'' in this SNPRM. We emphasize, however, that 
this SNPRM does not require installation of a nitrogen generation 
system or other FRM. The actions specified in this SNPRM will correct a 
specific, known unsafe condition with the FQIS. We decided to propose 
this AD action without specific service information for the expected 
design solution specifically because Boeing has not to date provided a 
design solution specific to FQIS. As a result of considering the 
comments to the NPRM (77 FR 12506, March 1, 2012), the FAA has 
identified a less costly option for Model 757 cargo airplanes. We have 
asked Boeing to develop service information for that option, and Boeing 
has agreed. Since the FAA already requires the vast majority of 
passenger airplanes registered in the U.S. to be equipped with FRM and 
we defined incorporation of FRM as one method of compliance within the 
NPRM (77 FR 12506, March 1, 2012), and because Boeing and Goodrich 
provided information to show that a specific FQIS protection solution 
would have a per-airplane cost similar to that of Boeing's FRM design 
solution, we have determined there is no practical reason to require 
the manufacturer to provide a corrective action specific to FQIS for 
passenger airplanes. We have not further changed this SNPRM regarding 
this issue.

[[Page 9410]]

Request To Extend Compliance Time Pending Issuance of Service 
Information

    A4A requested that we revise the NPRM (77 FR 12506, March 1, 2012) 
to extend the compliance time from 60 months to ``a 96-month compliance 
period that commences one year after the effective date of the AD''--
for a total compliance time of 9 years. A4A noted that SFAR 88 (Special 
Federal Aviation Regulation No. 88 (``SFAR 88,'' Amendment 21-78, and 
subsequent Amendments 21-82 and 21-83) (http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgFAR.nsf/0/EEFB3F94451DC06286256C93004F5E07?OpenDocument)) required design 
solutions for non-compliant designs to be provided by December 6, 2002, 
and considered that the absence of service information reflects a 
failure of communication and coordination, presumably between the FAA 
and Boeing. A4A was concerned that Boeing's declaration that it does 
not intend to develop a design solution other than its existing 
nitrogen generation system indicates that the development of any other 
design solution would be technically challenging and time consuming. 
A4A also cited the implementation of the requirements of part 26 of the 
Federal Aviation Regulations (14 CFR part 26) as an example of the FAA 
underestimating the costs and time required to develop design 
solutions.
    We partially agree with the request to extend the compliance time. 
While we agree to provide additional time for manufacturers to develop 
service information, we acknowledge that service information is not 
likely to be available until several months after the final rule is 
issued. We disagree with the assertion that the delay in proposing an 
AD to address the FQIS latent-plus-one unsafe conditions on several 
transport airplane models reflects a failure to communicate and 
coordinate with design approval holders.
    In 2003, the FAA held a series of AD board meetings to decide which 
of the design areas identified in SFAR 88 design reviews as non-
compliant on Boeing airplanes would be classified as unsafe conditions 
requiring AD action. The FQIS latent-plus-one issue was identified as 
an unsafe condition for high flammability fuel tanks at that time for 
several models, including the Model 757. Several airplane models from 
other manufacturers were identified as having similar issues. However, 
during that same time period, the National Transportation Safety Board 
(NTSB) had recommended FAA action to require inerting systems for 
center fuel tanks, and the FAA was working with industry to develop a 
practical nitrogen generation system for new production and retrofit 
installations on transport airplanes. The FAA was also planning to 
propose a new rule requiring those systems to be installed on new and 
existing airplanes, as recommended by the NTSB. The FAA recognized 
that, if such a system was installed on a given set of airplanes, the 
unsafe condition determination for the center fuel tank latent-plus-one 
would be addressed due to the modified center fuel tank meeting the 
conditions for a low flammability fuel tank after installation of a 
nitrogen generation system.
    The FAA therefore decided to defer addressing the FQIS latent-plus-
one issue on the affected airplanes until after the outcome of the FTFR 
rulemaking process. Now that the rulemaking process is complete and the 
safety enhancement provided by the FTFR rule (73 FR 42444, July 21, 
2008) has been limited to certain airplanes (14 CFR part 121, 125, and 
129 passenger airplanes), the FAA is addressing the FQIS latent-plus-
one unsafe conditions on the airplanes that are not required to receive 
the safety enhancement of the FTFR rule. This history was discussed in 
detail in the NPRM (77 FR 12506, March 1, 2012) and in the preamble for 
the FTFR rule.
    We disagree with extending the compliance time to 9 years. Service 
information to support the modification portion of the option for cargo 
airplanes is expected to be available shortly after the final rule is 
issued. The service information for the inspection portion of that 
option and the FRM option is already released. We have determined that 
a compliance time extension to 72 months for the modification will give 
adequate time for manufacturers to complete the remaining service 
information and for operators to complete the modification.
    We have revised the compliance time in this SNPRM to 72 months 
after the effective date of the AD.

Request To Reduce Compliance Time

    NATCA requested that we reduce the compliance time from 60 months 
to 36 months because of the time that has already passed to address 
this unsafe condition since its identification in 2003.
    While we acknowledge the time that has passed since the 
identification of the unsafe condition identified in this SNPRM, the 
FAA delayed taking action for this issue while we developed the FTFR 
rule (73 FR 42444, July 21, 2008), determined its applicability, which 
directly affected the applicability of this SNPRM, and implemented the 
FTFR rule. Now that we are proposing action for the affected airplanes, 
we must consider the ability of industry to develop an appropriate 
design change and incorporate it on all affected airplanes; we find 
that it is not practical for industry to respond to this AD in only 3 
years. We have therefore not reduced the compliance time in this SNPRM.

Request To Revise Cost Estimate Based on New Data

    Boeing requested that we revise the cost estimate specified in the 
NPRM (77 FR 12506, March 1, 2012) because the actual cost to develop 
and implement a design change to fully address the FQIS latent-plus-one 
failure conditions would be significantly higher. Boeing estimated in 
their comment that the cost to develop and implement a transient 
suppression unit design for Model 757 airplanes would be about the same 
as the cost of Boeing's FRM provided for the airplanes affected by the 
FTFR rule (73 FR 42444, July 21, 2008): in excess of $300,000 per 
airplane for airplanes equipped with the early FQIS design, and in 
excess of $200,000 per airplane for airplanes equipped with a Goodrich 
FQIS.
    In a subsequent meeting initiated by the FAA to obtain more detail 
on this cost estimate, Boeing provided a higher cost estimate than they 
provided in their written comment. However, in subsequent discussions 
with Boeing as part of developing this SNPRM, Boeing indicated that 
they were working on an isolation-based design alternative to the FAA's 
proposed modification option for the cargo airplanes that would likely 
be significantly less costly than the FAA's proposed cargo airplane 
option of partial wire separation.
    We partially agree with the commenter. We agree to revise the cost 
estimate because both Boeing and one of Boeing's affected FQIS vendors 
provided similar cost estimates that were higher than the estimates 
made in the NPRM (77 FR 12506, March 1, 2012) by the FAA. We disagree 
to revise the cost estimate as Boeing proposed. We have received 
several inconsistent cost estimates from industry during the 
development of the FTFR rule (73 FR 42444, July 21, 2008), in their 
written comments to the NPRM, and during discussions of the FAA's 
proposed alternative for cargo airplanes. We have therefore provided a 
revised cost estimate for the originally proposed action based on input 
from Boeing's written comment and from the FQIS vendor. We also have 
considered that it

[[Page 9411]]

is likely that aftermarket vendors may develop competing design 
solutions, as has occurred for other similar ADs, and those solutions 
will likely cost less than the original manufacturer's solutions.
    In addition, we have identified an additional compliance option--
with a different cost--for cargo airplanes. That cost estimate is based 
on Model 757 service information that described a very similar 
modification. We have used the work-hour estimate from that service 
bulletin, increased the work-hour estimate by 20 percent to account for 
any unforeseen increases in the work, and increased the parts prices to 
account for inflation and the potential that additional parts may be 
needed.

Request To Revise Cost Estimate Based on AD Scope

    Goodrich requested that, if the intent of the NPRM (77 FR 12506, 
March 1, 2012) is to protect all fuel tanks rather than just the center 
fuel tank, we revise the cost estimate of the NPRM accordingly. 
Goodrich stated that the cost estimate is based on three assumptions: 
(1) That current technology circuit isolation devices similar to those 
previously approved for other models would be acceptable, (2) that no 
further changes to airplane wiring would be required, and (3) that the 
design change would be required to protect only the center fuel tank. 
Goodrich noted that protection for all fuel tanks is required for the 
two similar ADs: AD 99-03-04, Amendment 39-11018 (64 FR 4959, February 
2, 1999), for Model 737 airplanes; and AD 98-20-40, Amendment 39-10808 
(63 FR 52147, September 30, 1998), for Model 747 airplanes. Goodrich 
requested that we revise the cost estimate if the AD's intent is to 
require protection for fuel tanks other than the center fuel tank or if 
other wiring change requirements are anticipated. Goodrich stated that 
the cost specified in the NPRM should be estimated based on the actual 
design changes expected, rather than on previous AD actions.
    We provide the following clarification of the intended scope of the 
NPRM (77 FR 12506, March 1, 2012) and the associated cost estimate 
regarding which fuel tanks are subject to the proposed requirements. AD 
99-03-04, Amendment 39-11018 (64 FR 4959, February 2, 1999), and AD 98-
20-40, Amendment 39-10808 (63 FR 52147, September 30, 1998), affect 
FQIS designs that are considered to have a higher level of risk of a 
fuel tank ignition source than the systems used on Model 757 airplanes. 
In addition, those systems were identical or nearly identical to the 
FQIS that was determined by the NTSB to be the most likely cause of the 
1996 Model 747-100 accident described in the NPRM. Because the latent-
plus-one failure scenario was suspected of actually having occurred on 
that system type, we determined that corrective action for all fuel 
tanks was appropriate. This decision was consistent with the 
subsequently published FAA policy on SFAR 88 AD decision criteria 
(section 25.981(a)(3) of the Federal Aviation Regulations (14 CFR 
25.981(a)(3))) (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/73716)). Also, it was our understanding that the design of that FQIS 
was such that, due to wiring interconnections between fuel tanks, it 
was necessary to protect the circuits for all fuel tanks in order to 
achieve effective protection for any one fuel tank.
    We have determined that the FQIS used on earlier production Model 
757 airplanes has the same fuel tank interconnection issue, but that 
the Goodrich system used on later production Model 757 airplanes does 
not have that issue. Since the cost estimates provided by both Boeing 
and Goodrich were based on design solutions that included upgrading to 
a Goodrich FQIS, we assume that the level of circuit protection for the 
center fuel tank can be significantly increased relative to the 
existing Goodrich design without having to further alter circuits or 
wiring for the main fuel tanks (beyond the alterations necessary to 
replace the FQIS with the Goodrich FQIS).
    Because the latent-plus-one scenarios for Model 757 airplanes 
equipped with the Goodrich FQIS are classified as ``theoretical'' 
rather than ``known to have occurred'' under the FAA policy on SFAR 88 
AD decision criteria (section 25.981(a)(3) of the Federal Aviation 
Regulations (14 CFR 25.981(a)(3))) (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/73716)), we have determined in 
accordance with that policy that the corrective action for passenger 
airplanes must eliminate the potential for all theoretical latent-plus-
one scenarios to create an ignition source in the center fuel tank, 
which is classified under that policy as a high flammability fuel tank. 
The need to modify the circuits or wiring for the main fuel tanks to 
achieve that intent will depend on the proposed design solution and the 
existing configuration of the airplane.
    As stated previously, we have revised the cost estimate in this 
SNPRM. For the purpose of the cost estimate for passenger airplanes, we 
have assumed that the airplane will be upgraded to the Goodrich FQIS if 
necessary, and any further modifications will be to only the center 
fuel tank circuits or wiring. For the purpose of the additional 
proposed cargo airplane option, we have provided separate estimates for 
each design. For cargo airplanes equipped with the early 757 FQIS 
design, we have assumed that additional isolation of some main fuel 
tank wiring will be required. It is not necessary to change the 
proposed requirement itself in paragraph (g) of this SNPRM, which is 
very specific that protection is required for the center fuel tank.

Request To Revise Cost Estimate To Consider Long-Term Effect of AD

    Goodrich asked whether the cost estimate specified in the NPRM (77 
FR 12506, March 1, 2012) considers the expectation that the affected 
fleet will be in operation for at least 20 more years, and that a 
complete redesign of the FQIS would need to be considered to ensure the 
availability of key FQIS electrical components. Goodrich stated this 
concern could drive potential development costs higher.
    We agree with the commenter's assertion. We did consider that the 
affected fleet will be in service for a considerable period of time. In 
the cost estimate in the NPRM (77 FR 12506, March 1, 2012), we assumed 
that the existing FQIS could be modified to meet the intent of the AD. 
However, comments from Boeing and Goodrich led us to recognize that it 
was likely that operators of airplanes with the early 757 FQIS design 
will likely need to be upgraded to the later Goodrich FQIS. The cost 
estimates used in this SNPRM for the fully compliant FQIS option (as 
opposed to the newly added cargo airplane option) are based on the 
estimates provided by Boeing and Goodrich. We previously described 
changes to the cost estimate in this SNPRM, but no further change is 
necessary regarding this issue.

Request To Explain Delay in Rulemaking and Identify Planned SFAR 88 ADs

    A4A requested that we explain the delay in rulemaking for this 
issue, and identify any further planned SFAR 88 ADs. A4A asked why the 
NPRM (77 FR 12506, March 1, 2012) was issued approximately 10 years 
after the identification of the unsafe conditions and development of 
design solutions was required to be completed under SFAR 88. A4A 
further asked that the FAA provide information on any other

[[Page 9412]]

designs that were already reviewed under SFAR 88, and provide industry 
with information regarding their planned disposition.
    We have specifically discussed these issues in the preamble to the 
FTFR rule (73 FR 42444, July 21, 2008) and the NPRM (77 FR 12506, March 
1, 2012), and explained the reasons for the delay in the response to 
``Request to Extend Compliance Time Pending Issuance of Service 
Information'' in this SNPRM. We cannot provide additional information 
on the results of design reviews and the planned disposition of issues 
identified in those design reviews because that information is 
proprietary. The FAA has not made available to the public an overall 
list of the specific product issues identified and the plans to address 
those issues, but operators can request the design review results from 
the manufacturers. We will likely propose additional AD rulemaking, and 
the public will be notified of those proposals via NPRMs. We have not 
changed this SNPRM regarding this issue.

Request To Explain Timing of NPRM (77 FR 12506, March 1, 2012) and 
Deficiencies of Affected Design

    FedEx requested that we explain what is non-compliant about the 
affected design and why we are proposing this design change at this 
late date. FedEx stated that Boeing and Goodrich determined in their 
safety reviews that only the FQIS densitometer was non-compliant.
    We agree to provide further explanation. This SNPRM addresses the 
question about the timing of this proposal under ``Request to Extend 
Compliance Time Pending Issuance of Service Information'' in this 
SNPRM. Boeing and Goodrich did identify that the densitometer of the 
Goodrich system had the potential for a single failure to cause an 
ignition source in a fuel tank. That issue was addressed by AD 2009-06-
20, Amendment 39-15857 (74 FR 12236, March 24, 2009). However, the 
Boeing safety review and the FAA SFAR 88 AD Board also identified the 
potential for a failure in airplane wiring outside the fuel tank or in 
the FQIS processor unit that, combined with a pre-existing latent 
failure of wiring or certain types of probe contamination inside the 
fuel tank, could cause an ignition source. These identified failure 
combinations were considered to be non-compliant with section 25.901(c) 
of the Federal Aviation Regulations (14 CFR 25.901(c)) and section 
25.981 of the Federal Aviation Regulations (14 CFR 25.981). We have not 
changed this SNPRM regarding this issue.

Request for Independent Review Regarding Timeliness of AD

    NATCA requested an independent review to identify and document how 
this issue was allowed to go unaddressed for 16 years since the TWA 
accident and 9 years since SFAR 88 required the development of service 
information. The commenter requested that the findings from that review 
be published.
    We acknowledge that there have been significant delays in 
addressing the issue that is the subject of this SNPRM. We are also 
fully aware of the events and factors that have led to those delays. We 
infer that NATCA made the request to ensure that the public is aware of 
those events and factors. We have described those events and factors in 
the NPRM (77 FR 12506, March 1, 2012) and in the other comment 
responses included in this SNPRM, and therefore the FAA does not plan 
to conduct the proposed review. We have not changed this SNPRM 
regarding this issue.

Request To Clarify Compliance Times

    A4A requested that we revise the NPRM (77 FR 12506, March 1, 2012) 
to clarify that the compliance deadlines in the AD prevail over the 
compliance deadlines in section 121.1117 of the Federal Aviation 
Regulations (14 CFR 121.1117) for any airplane for which the operator 
has chosen to comply with the AD by installing FRM.
    The proposed compliance times reflect the desired interpretation of 
the commenter as they pertain to cargo airplanes and airplanes that are 
not operated per part 121, part 125, or part 129 of the Federal 
Aviation Regulations (14 CFR part 121, 14 CFR part 125, or 14 CFR part 
129). Passenger airplanes operating under part 121, part 125, or part 
129 of the Federal Aviation Regulations (14 CFR part 121, 14 CFR part 
125, or 14 CFR part 129) must meet the compliance deadlines established 
in those operating rules. No change to this SNPRM is necessary 
regarding this issue.

Request To Clarify Master Minimum Equipment List (MMEL) Relief

    A4A requested that we revise the NPRM (77 FR 12506, March 1, 2012) 
to clarify that the MMEL relief provided for the Boeing NGS also 
applies to airplanes for which the operator has chosen to comply with 
the AD by installing an FRM such as the Boeing NGS.
    We acknowledge the commenter's concern. The revised applicability 
statement in paragraph (c) of this SNPRM excludes airplanes that are 
``equipped with a flammability reduction means (FRM) approved by the 
FAA. . . .'' That exclusion does not state that the installed equipment 
must be operative. However, installed equipment is required to be 
operative by sections 121.628, 125.201, and 129.14 of the Federal 
Aviation Regulations (14 CFR 121.628, 14 CFR 125.201, and 14 CFR 
129.14) except as allowed by the MMEL and the operator's approved 
minimum equipment list (MEL). Dispatch with an inoperative FRM under 
the MMEL is not prohibited by the AD, and our intent is to allow such 
operation. We have not further changed this SNPRM regarding this issue.

Request To Clarify Airplanes Excluded From Applicability

    A4A requested that we revise the NPRM (77 FR 12506, March 1, 2012) 
to clarify that airplanes equipped with FRM before conversion to all-
cargo operations are excluded from the proposed requirement to modify 
the FQIS.
    We agree to provide clarification. The revised applicability of 
this SNPRM excludes airplanes for which operators have installed FRM. 
No further change is necessary to this SNPRM regarding this issue. As 
noted above, the FRM must be operational with the exception of any 
relief granted under MMEL provisions.

Additional Change to NPRM (77 FR 12506, March 1, 2012)

    We have removed NOTE 1 of the NPRM (77 FR 12506, March 1, 2012). 
The note was included only as reminder that maintenance and/or 
preventive maintenance under 14 CFR part 43 is permitted provided the 
maintenance does not result in changing the AD-mandated configuration 
(reference 14 CFR 39.7).

FAA's Determination

    We are proposing this SNPRM because we evaluated all the relevant 
information and determined the unsafe condition described previously is 
likely to exist or develop in other products of the same type design. 
Certain changes described above expand the scope of the NPRM (77 FR 
12506, March 1, 2012). As a result, we have determined that it is 
necessary to reopen the comment period to provide additional 
opportunity for the public to comment on this SNPRM.

Proposed Requirements of the SNPRM

    This SNPRM would require modifying the FQIS wiring or fuel tank 
systems to prevent development of an ignition source inside the center 
fuel tank.

[[Page 9413]]

Costs of Compliance

    We estimate that this proposed AD affects 167 airplanes of U.S. 
registry. This estimate includes 148 cargo airplanes and 19 non-air-
carrier passenger airplanes. We estimate the following costs to comply 
with this proposed AD:

----------------------------------------------------------------------------------------------------------------
                Action                            Labor cost              Parts cost        Cost per product
----------------------------------------------------------------------------------------------------------------
                          Estimated Costs--Basic Proposed Requirement for All Airplanes
----------------------------------------------------------------------------------------------------------------
Fully correct FQIS vulnerability to     1,200 work-hours x $85 per            $200,000  $302,000.
 latent-plus-one failure conditions.     hour = $102,000.
----------------------------------------------------------------------------------------------------------------
                               Estimated Costs--Optional Actions for All Airplanes
----------------------------------------------------------------------------------------------------------------
Install FRM...........................  720 work-hours x $85 per hour         $323,000  $384,200.
                                         = $61,200.
----------------------------------------------------------------------------------------------------------------
                              Estimated Costs--Optional Actions for Cargo Airplanes
----------------------------------------------------------------------------------------------------------------
Wire separation.......................  230 work-hours x $85 per hour          $10,000  $29,550.
                                         = $19,550.
FQIS BITE check (required with wire     1 work-hour x $85 per hour =                 0  $85 per check (4 checks
 separation option).                     $85.                                            per year).
----------------------------------------------------------------------------------------------------------------

    Existing regulations already require that air-carrier passenger 
airplanes be equipped with FRM by December 26, 2017. We therefore 
assume that the FRM installation specified in paragraph (g) of this 
SNPRM would be done on only the 19 affected non-air-carrier passenger 
airplanes, for an estimated passenger fleet cost of $5,738,000. We also 
assume that the operators of the 148 affected cargo airplanes would 
choose the less costly actions specified in paragraph (h) of this AD, 
at an estimated cost of $4,373,400 for the wire separation 
modification, plus $50,320 annually for the BITE checks.

Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to 
issue rules on aviation safety. 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.
    We are issuing this rulemaking under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701: ``General 
requirements.'' Under that section, Congress charges the FAA with 
promoting safe flight of civil aircraft in air commerce by prescribing 
regulations for practices, methods, and procedures the Administrator 
finds necessary for safety in air commerce. This regulation is within 
the scope of that authority because it addresses an unsafe condition 
that is likely to exist or develop on products identified in this 
rulemaking action.

Regulatory Findings

    We determined that this proposed AD would not have federalism 
implications under Executive Order 13132. This proposed AD 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.
    For the reasons discussed above, I certify this proposed 
regulation:
    (1) Is not a ``significant regulatory action'' under Executive 
Order 12866,
    (2) Is not a ``significant rule'' under the DOT Regulatory Policies 
and Procedures (44 FR 11034, February 26, 1979),
    (3) Will not affect intrastate aviation in Alaska, and
    (4) Will not have a significant economic impact, positive or 
negative, on a substantial number of small entities under the criteria 
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

0
1. The authority citation for part 39 continues to read as follows:

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

Sec.  39.13  [Amended]

0
2. The FAA amends Sec.  39.13 by adding the following new airworthiness 
directive (AD):

The Boeing Company: Docket No. FAA-2012-0187; Directorate Identifier 
2011-NM-094-AD.

(a) Comments Due Date

    We must receive comments by April 24, 2015.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to The Boeing Company Model 757-200, -200PF, -
200CB, and -300 series airplanes; certificated in any category; 
except airplanes equipped with a flammability reduction means (FRM) 
approved by the FAA as compliant with the Fuel Tank Flammability 
Reduction (FTFR) rule (73 FR 42444, July 21, 2008) requirements of 
section 25.981(b) or section 26.33(c)(1) of the Federal Aviation 
Regulations (14 CFR 25.981(b) or 14 CFR 26.33(c)(1)).

(d) Subject

    Joint Aircraft System Component (JASC) Code 7397: Engine fuel 
system wiring.

(e) Unsafe Condition

    This AD was prompted by fuel system reviews conducted by the 
manufacturer. We are issuing this AD to prevent development of an 
ignition source inside the center fuel tank caused by a latent in-
tank failure combined with electrical energy transmitted into the 
center fuel tank via the fuel quantity indicating system (FQIS) 
wiring due to a single out-tank failure.

(f) Compliance

    Comply with this AD within the compliance times specified, 
unless already done.

(g) Modification

    Within 72 months after the effective date of this AD, modify the 
FQIS wiring or fuel tank systems to prevent development of an 
ignition source inside the center fuel tank, using a method approved 
in accordance with the procedures specified in paragraph (i) of this 
AD.

(h) Optional Actions for Cargo Airplanes

    For airplanes used exclusively for cargo operations: As an 
option to the requirements of paragraph (g) of this AD, do the 
actions

[[Page 9414]]

specified in paragraphs (h)(1) and (h)(2) of this AD, using methods 
approved in accordance with the procedures specified in paragraph 
(i) of this AD.
    (1) Within 6 months after the effective date of this AD, record 
the existing fault codes stored in the FQIS processor and then do a 
BITE check (check of built-in test equipment) of the FQIS, in 
accordance with the Accomplishment Instructions of Boeing Service 
Bulletin 757-28-0136, dated June 5, 2014. If any fault codes are 
recorded prior to the BITE check or as a result of the BITE check, 
before further flight, do all applicable repairs and repeat the BITE 
check until a successful test is performed with no faults found, in 
accordance with Boeing Service Bulletin 757-28-0136, dated June 5, 
2014. Repeat these actions thereafter at intervals not to exceed 750 
flight hours.
    (2) Within 72 months after the effective date of this AD, modify 
the airplane by separating FQIS wiring that runs between the FQIS 
processor and the center fuel tank, including any circuits that 
might pass through a main fuel tank, from other airplane wiring that 
is not intrinsically safe.

(i) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Seattle Aircraft Certification Office (ACO), 
FAA, has the authority to approve AMOCs for this AD, if requested 
using the procedures found in 14 CFR 39.19. In accordance with 14 
CFR 39.19, send your request to your principal inspector or local 
Flight Standards District Office, as appropriate. If sending 
information directly to the manager of the ACO, send it to the 
attention of the person identified in paragraph (j) of this AD. 
Information may be emailed to: 9-ANM-Seattle-ACO-AMOC-Requests@faa.gov.
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the local flight standards district office/certificate holding 
district office.

(j) Related Information

    For more information about this AD, contact Jon Regimbal, 
Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle 
Aircraft Certification Office (ACO), 1601 Lind Avenue SW., Renton, 
Washington 98057-3356; phone: 425-917-6506; fax: 425-917-6590; 
email: jon.regimbal@faa.gov.

    Issued in Renton, Washington, on December 18, 2014.
Jeffrey E. Duven,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2015-03540 Filed 2-20-15; 8:45 am]
BILLING CODE 4910-13-P