preamble attached >>>
ADs updated daily at www.Tdata.com
2020-18-13 THE BOEING COMPANY: Amendment 39-21234; Docket No. FAA-2016-6139; Product Identifier 2015-NM-061-AD.
(a) EFFECTIVE DATE

    This AD is effective October 29, 2020.

(b) AFFECTED ADS

    None.

(c) APPLICABILITY

    This  AD  applies  to  The Boeing Company  Model 737-600, -700, -700C,
    -800, -900, and -900ER series airplanes, certificated in any category,
    excluding airplanes  identified  in  paragraphs (c)(1) and (2) of this
    AD.

(1) Airplanes equipped  with a flammability reduction means (FRM) approved
    by  the  FAA  as compliant  with  the fuel tank flammability reduction
    (FTFR) requirements of 14 CFR 25.981(b) or 26.33(c)(1).

(2) Airplanes equipped with an ignition mitigation means (IMM) approved by
    the FAA as compliant with the FTFR requirements of 14 CFR 25.981(c) or
    26.33(c)(2).

(d) SUBJECT

    Air Transport Association (ATA) of America Code 28, Fuel.

(e) UNSAFE CONDITION

    This AD  was prompted  by the  FAA's analysis  of the  Model 737  fuel
    system reviews conducted by the manufacturer.  The FAA is issuing this
    AD to prevent ignition sources inside the center fuel tank, which,  in
    combination with flammable fuel vapors,  could  result in a  fuel tank
    explosion and consequent loss of the airplane.

(f) COMPLIANCE

    Comply with this AD within the compliance times specified,  unless al-
    ready done.

(g) MODIFICATION

    Within 72 months after the effective date of this AD,  modify the fuel
    quantity  indicating  system  (FQIS)  to  prevent  development  of  an
    ignition source inside  the center fuel  tank due to  electrical fault
    conditions, using a method approved in accordance with the  procedures
    specified in paragraph (i) of this AD.

(h) ALTERNATIVE ACTIONS FOR CARGO AIRPLANES

    For airplanes used exclusively for cargo operations: As an alternative
    to  the requirements  of paragraph  (g) of  this AD,  do  the  actions
    specified  in  paragraphs  (h)(1) and  (2) of  this AD,  using methods
    approved in accordance with the procedures specified in paragraph  (i)
    of this AD. To exercise  this alternative, operators must perform  the
    first inspection required under paragraph  (h)(1) of  this AD within 6
    months  after  the  effective  date  of  this  AD.  To  exercise  this
    alternative for airplanes returned to service after conversion of  the
    airplane from a passenger configuration to an all-cargo  configuration
    more than 6 months after the effective date of this AD, operators must
    perform the first inspection  required under paragraph (h)(1)  of this
    AD prior to further flight after the conversion.

(1) Within 6 months after the effective date of this AD, record the exist-
    ing fault codes stored in the FQIS processor and before further flight
    thereafter do a BITE check  (check of built-in test equipment)  of the
    FQIS.  If any nondispatchable fault code is 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 nondispatchable  faults found,  using a  method
    approved in accordance with the procedures specified  in paragraph (i)
    of this AD. Repeat these actions thereafter at intervals not to exceed
    750 flight hours.  Modification  as specified  in  paragraph (h)(2) of
    this AD does  not terminate the  repetitive BITE check  requirement of
    this paragraph.

(2) Within 72 months after the effective date of this AD,  modify the air-
    plane by separating FQIS wiring  that runs between the FQIS  processor
    and the  center tank  wing spar  penetrations, including  any circuits
    that might pass through a  main fuel tank, from other  airplane wiring
    that is not intrinsically  safe, using methods approved  in accordance
    with the procedures specified in paragraph (i) of this AD.

(i) ALTERNATIVE METHODS OF COMPLIANCE (AMOCS)

(1) The  Manager,  Seattle ACO Branch,  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
    certification  office,  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 in-
    spector,  or  lacking a principal inspector,  the manager of the local
    flight standards district office/certificate holding district office.

(3) An AMOC that provides an acceptable level of safety  may  be  used for
    any repair,  modification,  or alteration required by this AD if it is
    approved  by The Boeing Company Organization Designation Authorization
    (ODA) that has been authorized by the Manager, Seattle ACO Branch, FAA
    to make those findings.  To be approved,  the repair method, modifica-
    tion deviation,  or  alteration deviation  must meet the certification
    basis of  the airplane,  and the  approval must  specifically refer to
    this AD.

(j) RELATED INFORMATION

    For more information about this AD,  contact  Jon Regimbal,  Aerospace
    Engineer,  Propulsion  Section,  FAA,  Seattle ACO Branch,  2200 South
    216th St., Des Moines, WA 98198;  phone and fax: 206-231-3557;  email:
    Jon.Regimbal@faa.gov.

(k) MATERIAL INCORPORATED BY REFERENCE

    None.

Issued on August 26, 2020. Lance T Gant, Director, Compliance & Airworthi-
ness Division, Aircraft Certification Service.

FOR FURTHER INFORMATION CONTACT: Jon Regimbal, Aerospace Engineer, Propul-
sion Section, FAA, Seattle ACO Branch, 2200 South 216th St, Des Moines, WA
98198; phone and fax: 206-231-3557; email: Jon.Regimbal@faa.gov.
PREAMBLE 

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2016-6139; Product Identifier 2015-NM-061-AD; Amendment
39-21234; AD 2020-18-13]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: The FAA is adopting a new airworthiness directive (AD) for
certain The Boeing Company Model 737-600, -700, -700C, -800, -900, and
-900ER series airplanes. This AD was prompted by the FAA's analysis of
the Model 737 fuel system reviews conducted by the manufacturer. This
AD requires modifying the fuel quantity indicating system (FQIS) to
prevent development of an ignition source inside the center fuel tank
due to electrical fault conditions. This AD also provides alternative
actions for cargo airplanes.

The FAA is issuing this AD to address the unsafe condition on these
products.

DATES: This AD is effective October 29, 2020.

ADDRESSES:

Examining the AD Docket

You may examine the AD docket on the internet at https://www.regulations.gov
by searching for and locating Docket No. FAA-2016-
6139; or in person at Docket Operations between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays. The AD docket contains
this final rule, any comments received, and other information. The
address for Docket Operations is U.S. Department of Transportation,
Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200
New Jersey Avenue SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Jon Regimbal, Aerospace Engineer,
Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3557; email:
Jon.Regimbal@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 by adding an AD that would apply to certain The Boeing
Company Model 737-600, -700, -700C, -800, -900, and -900ER series
airplanes. The NPRM published in the Federal Register on May 3, 2016
(81 FR 26485). The NPRM was prompted by the FAA's analysis of the Model
737 fuel system reviews conducted by the manufacturer. The NPRM
proposed to require modifying the FQIS to prevent development of an
ignition source inside the center fuel tank due to electrical fault
conditions. The NPRM also proposed to provide alternative actions for
cargo airplanes.
The FAA is issuing this AD to address ignition sources inside the
center fuel tank, which, in combination with flammable fuel vapors,
could result in a fuel tank explosion and consequent loss of the
airplane.

Comments

The FAA gave the public the opportunity to participate in
developing this final rule. The following presents the comments
received on the NPRM and the FAA's response to each comment.

Support for the NPRM

The Air Line Pilots Association, International (ALPA) and National
Air Traffic Controllers Association (NATCA) supported the intent of the
NPRM. Additional comments from NATCA are addressed below.

Request To Withdraw NPRM: Unjustified by Risk

Airlines for America and the Cargo Airline Association, in
consolidated comments (A4A/CAA), and KLM Royal Dutch Airlines (KLM)
requested that the FAA withdraw the NPRM. A4A/CAA cited comments
submitted by Boeing to Docket No. FAA-2012-0187 in which Boeing stated
that the risk is ``less than extremely improbable'' and that Boeing
does not believe that an unsafe condition exists. A4A/CAA noted that
they consider the Boeing comments to be applicable to the airplane
models in the NPRM. KLM stated that the NPRM does not clarify the
necessity of additional actions beyond current requirements. KLM added
that it understands that Boeing is not able to explain or substantiate
the rationale behind the NPRM.
The FAA disagrees with the commenters' request. The FAA notes that
Boeing's comments were addressed in the supplemental NPRM (SNPRM) for
Docket No. FAA 2012-0187 (80 FR 9400, February 23, 2015) in the comment
response for ``Request To Withdraw NPRM (77 FR 12506, March 1, 2012):
Unjustified by Risk.'' As explained in that comment response, in
addition to examining average risk and total fleet risk, the FAA
examines the individual flight risk on the worst reasonably anticipated
flights. In general, the FAA issues ADs in cases where reasonably
anticipated flights with preexisting 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. The FAA
has determined that the current requirements, including airworthiness
limitations and critical design configuration control limitations
(CDCCLs) do not adequately address the unsafe condition identified in
this AD and therefore it is necessary to issue this final rule. The FAA
has not changed this AD regarding this issue.

Request To Withdraw NPRM: Probability Analysis Inconsistent With
Regulatory Requirements


A4A/CAA requested that the FAA withdraw the NPRM. A4A/CAA stated
that the assumption of a single failure regardless of probability is
inconsistent with 14 CFR part 25 regulatory requirements. A4A/CAA
referred to the phrase ``regardless of probability'' associated with
single failures. A4A/CAA acknowledged that the term is used with single
failures in FAA Advisory Circular (AC) 25.981-1C,\1\ ``Fuel Tank
Ignition Source Prevention Guidelines,'' but since that term does not
appear in 14 CFR 25.981(a)(3), the commenter considered its use
arbitrary, possibly introducing additional requirements not included in
that section. A4A/CAA stated that the ``worst reasonably anticipated
flight'' is a flight with a latent FQIS failure and a high-flammability
tank, and this ``latent plus one'' failure--regardless of probability
of a single failure--is not consistent with 14 CFR 25.981(a)(3).
---------------------------------------------------------------------------
\1\ https://www.faa.gov/documentLibrary/media/Advisory_Circular/
AC_25.981-1C.pdf.
---------------------------------------------------------------------------

The FAA disagrees with the commenter's request. The FAA notes that
the commenter's assertion about the intent of 14 CFR 25.981(a)(3) is
incorrect based on both the language of the rule and on the published
rulemaking documents. The absence of a probabilistic qualifier in both
the ``from each single failure'' clause and in the ``from each single
failure in combination with each latent failure not shown to be
extremely remote'' clause in 14 CFR 25.981(a)(3) in fact means just
that--there is no probabilistic qualifier intended by the regulation.
The intent for single failures in these two scenarios to be considered
regardless of probability of the single failure was explicitly stated
in the NPRM for 14 CFR 25.981, as amended by amendment 25-102 (66 FR
23085, May 7, 2001) (``amendment 25-102''). That NPRM stated, in
pertinent part, that it would also add a new paragraph (a)(3) to
require that a safety analysis be performed to demonstrate that the
presence of an ignition source in the fuel tank system could not result
from ``any single failure, from any single failure in combination with
any latent failure condition not shown to be extremely remote, or from
any combination of failures not shown to be extremely improbable.''
These new requirements would define three scenarios that must be
addressed in order to show compliance with the proposed paragraph
(a)(3). ``The first scenario is that any single failure, regardless of
the probability of occurrence of the failure, must not cause an
ignition source. The second scenario is that any single failure,
regardless of the probability occurrence, in combination with any
latent failure condition not shown to be at least
extremely remote (i.e., not shown to be extremely remote or extremely
improbable), must not cause an ignition source. The third scenario is
that any combination of failures not shown to be extremely improbable
must not cause an ignition source.''
The preamble to the final rule for amendment 25-102 made a nearly
identical statement, including the same uses of the phrase ``regardless
of probability.'' The FAA has determined that it is necessary to
proceed with issuance of this final rule as proposed. Further details
and a description of the FAA's risk assessment can be found in
responses to similar comments in a related SNPRM that addressed the
same unsafe condition for Model 757 airplanes, in Docket No. FAA-2012-
0187, and in the subsequently issued final rule, AD 2016-07-07,
amendment 39-18452 (81 FR 19472, April 5, 2016) (``AD 2016-07-07''). No
change to this AD was made in response to these comments.

Request To Withdraw NPRM: No New Data Since Fuel Tank Flammability
Reduction (FTFR) Rulemaking


A4A/CAA requested that the FAA withdraw the NPRM based on a lack of
new data since the issuance of the FTFR rule (73 FR 42444, July 21,
2008). A4A/CAA referred to the FTFR rule and decision to not require
flammability reductions means (FRM) for all-cargo airplanes, and the
FAA's intent to gather additional data and consideration of further
rulemaking if flammability of these airplanes is excessive. A4A/CAA
stated that since the FTFR rule, no additional data has been publicly
introduced that would support or justify the applicability of this
rulemaking to all-cargo aircraft. A4A/CAA also referred to the FAA's
response to comments in the preamble to the SNPRM for Docket No. FAA-
2012-0187, which documented the FAA's decision on applicability of FRM
and cost estimates. A4A/CAA stated that the FAA response was misleading
and not factual since manufacturers did not begin detailed designs to
address the proposed unsafe condition until after the FTFR rule was
published. A4A/CAA added that the FAA did not discuss other changes to
the FQIS system in the FTFR rule.
The FAA disagrees with the commenter's request. The FAA notes that
the FTFR rule and FQIS ADs are two different issues with separate FAA
actions. The intent of the FTFR rule was to provide an order of
magnitude reduction in the rate of fuel tank explosions for the
airplanes affected by that rule through adding a new airworthiness
standard for the flammability of fuel tanks. The FAA notes that the
FTFR rule was never intended to be a replacement for the issuance of
ADs to address identified unsafe conditions. An unsafe condition due to
the identified FQIS latent-plus-single failure issue in high-
flammability fuel tanks was determined to exist during the Special
Federal Aviation Regulation (SFAR) 88 AD Board held by the FAA in 2003
using the guidance in FAA Policy Memorandum ANM100-2003-112-15, ``SFAR
88--Mandatory Action Decision Criteria,'' dated February 25, 2003,\2\
for high-flammability fuel tanks, including the center fuel tank on
Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes.
That same issue was not considered to be an unsafe condition in low-
flammability wing fuel tanks based on that same policy memorandum. The
FAA has not changed this AD regarding this issue.
---------------------------------------------------------------------------
\2\ http://rgl.faa.gov/Regulatory_and_Guidance_Library/
rgPolicy.nsf/0/dc94c3a46396950386256d5e006aed11/$FILE/Feb2503.pdf.
---------------------------------------------------------------------------

Request To Withdraw NPRM: Arbitrary and Inconsistent Wire Separation
Standards


A4A/CAA requested that the FAA withdraw the NPRM based on a lack of
consistent design standards for FQIS wire separation. A4A/CAA assumed
that the approved standard for the retrofit is a 2-inch wire separation
minimum, which the commenter considered arbitrary and inconsistently
applied. A4A/CAA reported that the amount of wiring capable of meeting
that separation standard varies widely among airplane models. A4A/CAA
also acknowledged that other separation methods were used in areas not
meeting the 2-inch wire separation requirement.
The FAA does not agree with the commenter's request. The degree of
physical isolation of FQIS wiring from other wiring, whether provided
by physical distance or barrier methods, that is necessary to eliminate
the potential for hot shorts due to wiring faults is dependent on the
materials used, the wire securing methods, and the possible types of
wiring faults. The FAA relied on the manufacturer to assess the details
of the design and to propose the appropriate isolation measures. While
2 inches of physical separation may appear to be an arbitrary number,
it was the distance proposed by the manufacturer as appropriate for
their design based on analysis of the design details. The FAA has not
changed this AD regarding this issue.

Request To Withdraw NPRM: NPRM Arbitrary and Inconsistently Applied

A4A/CAA requested that the FAA withdraw the NPRM. A4A/CAA noted
that airplanes with FRM are not included in the applicability, and the
NPRM would therefore not fully address the unsafe condition. A4A/CAA
added that the distinction between high- and low-flammability exposure
time fuel tanks as used in the NPRM is arbitrary. A4A/CAA stated that
an arbitrary differentiation of high- versus low-flammability as
decisional criteria for the need for corrective action does not take
into account the actual probability of the impact of the difference in
flammability on the potential of catastrophic failure. A4A/CAA also
stated that allowing the proposed alternative actions for cargo
airplanes does not fully address the unsafe condition in the NPRM. A4A/
CAA referenced the FAA's response to comments in AD 2016-07-07
regarding this issue. The commenter summarized numerical analysis
showing no significant difference in risk between high- and low-
flammability fuel tanks. A4A/CAA concluded that the FAA's risk analysis
is arbitrary and an unsafe condition does not exist.
The FAA disagrees with the assertion that the NPRM is arbitrary and
inconsistent. The NPRM follows defined policy in FAA Policy Memorandum
ANM100-2003-112-15, and consistently applies the policy to several
airplane models with similar unsafe conditions, similar to AD 2016-07-
07. The FAA defined the difference between low- and high-flammability
exposure time fuel tanks based on recommendations from the Aviation
Rulemaking Advisory Committee Fuel Tank Harmonization Working Group
(FTHWG). The preamble to the final rule for amendment 25-102, which
amended 14 CFR 25.981, defined this difference as based upon comparison
of ``the safety record of center wing fuel tanks that, in certain
airplanes, are heated by equipment located under the tank, and unheated
fuel tanks located in the wing.'' The FTHWG concluded that the safety
record of fuel tanks located in the wings was adequate and that if the
same level could be achieved in center wing fuel tanks, the overall
safety objective would be achieved.
In the response to comments in the preamble to the final rule for
AD 2016-07-07 referenced by the commenter, the FAA described why FRM or
alternative actions for cargo airplanes provide an acceptable level of
safety, even if they do not completely eliminate the non-compliance
with 14 CFR 25.981(a)(3).

The fuel tank explosion history for turbojet/turbofan powered
transport airplanes fueled with kerosene type fuels, outside of
maintenance activity, has consisted of explosions of tanks that (1) are
not conventional aluminum wing tanks and (2) spend a considerable
amount of their operating time empty. The service history of
conventional aluminum wing tanks has been acceptable. The intent of the
difference in decision criteria in FAA Policy Memorandum ANM100-2003-
112-15 was intended to give credit for this satisfactory service
experience, and to differentiate between tanks with a level of
flammability similar to that of a conventional wing tank and those with
a significantly higher level of flammability.
The numerical analysis provided by the commenter is inconsistent
with the fuel tank explosion service history. There are at least three
identifiable physics-based reasons for that inconsistency. First, low-
flammability tanks on most types of airplanes are main tanks that are
the last tanks used. During a large portion of their operating time,
the systems and structural features that have the potential to be
ignition sources in the event of a failure condition are covered with
liquid fuel, and an ignition source, if it occurs, is likely to be
submerged. When a potential ignition source in a main tank is
uncovered, it is likely to be later in the flight when the tank is cool
and no longer flammable. The commenter's analysis does not account for
this significant effect. Second, the numerical analysis used by the
commenter assumes that any given ignition source has a random
occurrence in time at the estimated probability, and that, in order for
an explosion to occur, that random occurrence of an ignition source
needs to coincide with the tank being in a flammable state. In fact,
many of the identified ignition threats do not simply occur briefly and
then go away. Instead, a fault occurs that, until it is discovered and
corrected, repeatedly creates an ignition source, and repeatedly tests
whether flammable conditions exist.
Third, the flammability of low-flammability fuel tanks is typically
dependent on weather, and a low-flammability fuel tank may operate for
months without ever becoming flammable. This is not true of most high-
flammability fuel tanks, which typically have significant on-airplane
heat sources driving their temperature. This factor can mean that, on
some airplanes, an in-tank latent failure can occur and, after some
period of time, be detected and corrected without the low-flammability
tank ever having flammable conditions. The numerical analysis provided
by the commenter does not account for these significant factors. The
difference in likelihood of a failure that results in repeated ignition
source events causing a tank explosion is not simply proportional to
difference in the fleet average flammability of the tank for the
reasons stated above. The FAA has not changed this AD regarding this
issue.

Request To Withdraw NPRM: Overestimate of Fleet Average Flammability
Exposure for All-Cargo Fleet in Alaska


A4A/CAA requested that the FAA withdraw the NPRM. The commenter
stated that the FAA did not properly analyze the fleet average
flammability for the center wing tank on Model 737-700 airplanes. The
commenter stated that the known U.S. registered 737-700 all-cargo fleet
without FRM installed will be operated almost solely in the state of
Alaska for the foreseeable future. A4A/CAA noted that the mean average
ambient temperature in Alaska is much lower than that used in the FAA's
analysis. The commenter added that the air conditioning packs in an
all-cargo configuration generate significantly less heat transfer to
the center wing tank during normal operations than during the normal
operations assumed by the FAA's analysis. A4A/CAA concluded that these
factors reduce the fleet average flammability exposure for the all-
cargo Model 737-700 airplanes to the level of the main wing tanks, and
therefore, the unsafe condition does not exist.
The FAA does not agree to withdraw the NPRM. More than 1,100 Model
737-700 airplanes have been produced. The FAA foresees that, as these
airplanes are replaced in passenger service by newer airplanes, a
significant portion of them will be converted to all-cargo service and
will eventually fly throughout the U.S. and the world. Multiple cargo-
conversion designs for these airplanes have been approved, and other
conversion designs are in the approval process. The FAA does not agree
to base its decision about whether an AD is necessary for these
airplanes on a flammability analysis based solely on the initial cargo
conversions currently being largely operated in Alaska.
The FAA also does not agree that a new analysis considering
operation of only the initial cargo-converted airplanes would result in
a determination that the center fuel tank of those airplanes has a
level of flammability comparable to a wing tank of conventional
aluminum construction, and that the center fuel tank on those airplanes
could therefore legitimately be classified as a low-flammability fuel
tank. In addition, the FAA considers the unsafe condition determination
described in the SNPRM for Docket No. FAA-2012-0187, in the response to
comments section under, ``Request To Withdraw NPRM (77 FR 12506, March
1, 2012): Unjustified by Risk,'' to be applicable to these Model 737
airplanes.

Request To Remove Certain Business Jets From the Applicability

AMES Continuing Airworthiness Management Organization (AMES CAMO)
requested that the proposed AD be revised to exclude Boeing Business
Jets operated under 14 CFR part 91. AMES CAMO noted that the proposed
AD excludes airplanes modified by the nitrogen generation system (NGS)
system, but the NGS is mandated only on commercial airplanes operating
under 14 CFR part 121. AMES CAMO suggested the proposed AD should only
apply to airplanes operating under 14 CFR part 121.
The FAA disagrees with the commenter's request. Policy Memorandum
ANM100-2003-112-15 is applicable to large transport airplanes except
those specifically excluded by the Special Federal Aviation Regulation
(SFAR) No. 88 regulation (in 14 CFR part 21). The FAA did not exclude
non-air-carrier large transport airplanes from the other ADs determined
to be necessary as a result of SFAR 88, and included non-air-carrier
large transport airplanes in the FRM retrofit requirements added to 14
CFR part 125 in 2008. The unsafe condition addressed by this AD is
applicable to Model 737 airplanes operated as business jets, except as
specified in paragraph (c) of this AD. The FAA has not changed this AD
regarding this issue.

Request To Require Cargo Airplane Option for All Airplanes

Boeing and All Nippon Airways (ANA) requested that the NPRM be
revised to make the alternative actions for cargo airplanes specified
in paragraph (h) of the proposed AD applicable to all airplanes. Boeing
asked that the FAA provide a technical justification why the actions in
paragraph (h) of the proposed AD apply only to cargo airplanes. ANA
asked that the actions in paragraph (h) of the proposed AD be allowed
for passenger airplanes not subject to the FTFR rule, suggesting this
would provide more choices regarding how to comply with the proposed
AD.
The FAA disagrees with the commenters' requests. As discussed in
the comment response in the SNPRM
for Docket No. FAA-2012-0187, under the heading ``Requests To Withdraw
NPRM (77 FR 12506, March 1, 2012) Based on Applicability'' the FAA does
not consider the alternative action for cargo airplanes allowed by this
AD to provide an adequate level of safety for passenger airplanes. The
FAA is willing 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 not
changed this AD regarding this issue.

Request To Exclude Certain Airplanes

United Airlines (UAL) noted that the FRM required by 14 CFR
121.1117 will have been installed on all affected airplanes in
passenger configuration by December 26, 2018. The FAA infers UAL is
requesting that the FAA revise the proposed AD to exclude airplanes
that are affected by 14 CFR 121.1117. In addition, UAL suggested that
the FAA either delete paragraph (g) of the proposed AD or make
paragraph (g) of the proposed AD applicable only to airplanes in a
cargo configuration that do not have an FRM installed and non-U.S.-
registered airplanes that do not have to comply with FRM requirements.
The FAA disagrees with the commenter's request. There are other
passenger-carrying airplanes operated under 14 CFR part 91 that are not
required to install FRM. (The requirement to install FRM on all
passenger-carrying airplanes operated by air carriers is in 14 CFR
121.1117.) The FAA notes that foreign air carriers may not have to
comply with that requirement or similar requirements of their own civil
aviation authority. The European Union Aviation Safety Agency (EASA),
for example, has chosen not to require FRM to be retrofitted to in-
service airplanes. This AD is intended to require any Model 737-600, -
700, -700C, -800, -900, and -900ER series passenger airplane that does
not have FRM, regardless of the rules under which it is operated, to
address the FQIS latent-plus-one unsafe condition with a corrective
action that fully complies with the FAA's airworthiness standards. This
requirement fulfills the FAA's International Civil Aviation
Organization to address unsafe conditions on all of the aircraft
manufactured by the state of design, not just those aircraft whose
operation is under the jurisdiction of the state of design. The FAA has
not changed this AD regarding this issue.

Request To Clarify Certification Basis for Modification Requirements

NATCA recommended that the FAA revise paragraph (g) of the proposed
AD to clearly state that the required FQIS design changes must comply
with the fail-safe requirements of 14 CFR 25.901(c), as amended by
amendment 25-46 (43 FR 50597, October 30, 1978); and 14 CFR 25.981(a)
and (b), as amended by amendment 25-102; NATCA added that these
provisions are required by SFAR 88.
The FAA does not agree to change paragraph (g) of this AD. While
the FAA agrees that modifications to comply with paragraph (g) of this
AD should be required to comply with the referenced regulations, that
requirement already exists in 14 CFR part 21. No change to this AD is
necessary.

Request To Address Unsafe Condition on All Fuel Tanks

NATCA recommended that the FAA require design changes that
eliminate unsafe FQIS failure conditions on all fuel tanks on the
affected models, regardless of fuel tank location or the percentage of
time the fuel tank is flammable. NATCA referred to four fuel tank
explosions in low-flammability exposure time fuel tanks identified by
the FAA during FTFR rulemaking. NATCA stated that neither FRM nor
alternative actions for cargo airplanes (e.g., BITE checks (checks of
built-in test equipment) followed by applicable repairs before further
flight and modification of the center fuel tank FQIS wiring within 60
months) would bring the airplane into full regulatory compliance. NATCA
added that the combination of failures described in the NPRM meets the
criteria for ``known combinations'' of failures that require corrective
action in FAA Policy Memorandum ANM100-2003-112-15.
The FAA disagrees with the commenter's request. The FAA has
determined that according to Policy Memorandum ANM100-2003-112-15, the
failure condition for the airplanes affected by this AD should not be
classified as a ``known combination.'' While the FQIS design
architecture is similar to that of the early Boeing Model 747
configuration that is suspected of contributing to the TWA Flight 800
fuel tank explosion, significant differences exist in the design of
FQIS components and wire installations between the affected Boeing
models and the early Model 747 airplanes such that the intent of the
``known combinations'' provision for low-flammability fuel tanks in the
policy memorandum is not applicable. Therefore, this AD affects only
the identified Boeing airplanes with high-flammability exposure time
fuel tanks, as specified in paragraph (c) of this AD. The FAA provided
a detailed response to similar comments in the preamble of the final
rule for AD 2016-07-07. The FAA has not changed this final rule
regarding this issue.

Request To Require Modification on All Production Airplanes

NATCA recommended that the FAA require designs that comply with 14
CFR 25.901(c) and 25.981(a)(3) on all newly produced transport
airplanes. NATCA stated that continuing to grant exemptions to 14 CFR
25.901(c), as amended by amendment 25-40 (42 FR 15042, March 17, 1977);
and 14 CFR 25.981(a)(3), as amended by amendment 25-102; has allowed
continued production of thousands of airplanes with this known unsafe
condition.
The FAA disagrees with the commenter's request. The recommendation
to require production airplanes to fully comply with 14 CFR 25.901(c)
and 14 CFR 25.981(a)(3) is outside the scope of this rulemaking. In
addition, the FAA has implemented requirements for all large transport
airplanes produced after September 2010 to include flammability
reduction methods for tanks that would otherwise be high-flammability
fuel tanks. Boeing incorporated this change into the Model 737 series
airplanes that are still in production and the FAA has excluded those
models from the applicability of this AD. The FAA has not changed this
final rule regarding this issue.

Request To State That an Exemption is Required

Boeing requested that paragraph (h) of the proposed AD be revised
to state that an exemption is required to accomplish the specified
actions. Boeing stated that the FAA has identified that the BITE
procedure and wire separation design changes specified in the proposed
AD are not sufficient for compliance to 14 CFR 25.981(a) at the FQIS
level. Boeing stated that an exemption is therefore needed prior to
approval of the related design change.
The FAA agrees to clarify. The BITE check is not a type design
change or alteration, so no exemption from the airworthiness standards
is required for that action. The design data approval of any partial
wire separation modification would require an exemption. That exemption
would be obtained by the party seeking approval of the alteration data,
and no further exemption would be required for the party using that
data to alter an aircraft. Obtaining such an exemption would be part of the
certification process for such a change, so, the FAA does not find it
necessary to include such information in paragraph (h) of this AD. In
addition, some parties may choose to comply with the AD using a design
change that fully complies with the airworthiness standards. The FAA
also notes that the commenter appears to misunderstand why an exemption
is needed for the required modification. The exemption is needed
because, even with the modification, the FQIS does not comply with 14
CFR 25.901(c) and 14 CFR 25.981(a). The exemption does not authorize
evaluation of a partial system for compliance with the system level
requirement. The FAA has not changed this AD regarding this issue.

Request To Exclude Airplanes That Have Installed an Ignition Mitigation
Means (IMM) or Flammability Impact Mitigation Means (FIMM)


AerSale stated that the Costs of Compliance section of the NPRM
only cites the requirements in 14 CFR 121.1117 to install FRM, but 14
CFR 121.1117 paragraph (d)(1) states that IMM, FRM, or FIMM may be
installed. AerSale suggested that all IMM, FRM, or FIMM installations
with the approval of the FAA Oversight Office would meet the
requirements of 14 CFR 121.1117. The FAA infers AerSale is requesting
that the proposed AD be revised to exclude airplanes on which IMM or
FIMM has been installed.
The FAA partially agrees with the commenter's request. The FAA
agrees that IMM provides a level of risk reduction at least as great as
that provided by FRM. The FAA does not agree that airplanes should be
excluded from paragraph (c) of this AD based on the installation of
FIMM alone. FIMM is applicable to design changes only, and is intended
to ensure that, if a fuel tank design change would otherwise have
increased the flammability of a fuel tank, the associated FIMM would
ensure that the flammability of that tank is not increased by the
design change. Therefore, FIMM itself does not address the need for FRM
for the original tank design. The FAA has revised paragraph (c) of this
AD to clarify that airplanes with an IMM approved by the FAA as
compliant with certain regulations are excluded from this AD. This
revision includes adding paragraphs (c)(1) and (2) of this AD.

Request To Record Only Certain Codes

Boeing requested that paragraph (h)(1) of the proposed AD be
revised to only require corrective actions if a nondispatchable fault
code pertaining to the center wing tank is recorded (as opposed to any
nondispatchable fault code being recorded). Boeing stated that all FQIS
wire separation changes in the proposed AD are limited to the center
wing tank, therefore only built-in test equipment (BITE) check messages
pertaining to the center wing tank are applicable to the proposed AD.
In addition, Boeing stated that a final rule should be postponed until
the FAA develops a list of ``nondispatchable fault codes'' in
conjunction with Boeing.
The FAA agrees that the unsafe condition addressed by this AD is
limited to the center wing tank. However, the FAA does not agree that
the AD should be changed as proposed by Boeing. It is not clear to the
FAA whether there may be FQIS BITE fault codes that are not clearly
identified as related to the center wing tank but that may impact
center tank circuits. Therefore, the FAA has determined that all
nondispatchable fault codes recorded prior to the BITE check or as a
result of the BITE check required by paragraph (h)(1) of this AD must
be addressed. Operators or Boeing may request an alternative method of
compliance (AMOC) under the provisions of paragraph (i) of this AD if
they can provide sufficient data that a particular fault code does not
pertain to the unsafe condition addressed by this AD.
Regarding the requirement to record and address fault codes read
immediately prior to running the BITE check procedure, the FAA notes
that the normal Boeing procedure for performing an FQIS BITE check is
to first erase all of the existing fault codes, then perform the BITE
check and troubleshoot any resulting new fault codes. For this AD, the
FAA did not want any already stored fault codes to be potentially
ignored due to erasure at the first step because some of the failures
of concern can be intermittent. This AD therefore requires operators to
record the existing codes before doing the BITE check, then do the BITE
check and record the new codes that result from that BITE check, and
then do the appropriate troubleshooting and corrective action for both
sets of codes per the manufacturer's guidance. The FAA has not changed
this AD regarding this issue.
Finally, the FAA does not agree to delay the final rule while
Boeing proposes and obtains FAA agreement on a list of nondispatchable
fault codes. The FAA requested service information from Boeing in 2016
to support the option for all-cargo airplanes on all of the Boeing
models for which similar FQIS ADs were planned. Boeing chose at that
time to develop service information only for the Model 747-400, 757,
and 767 airplanes because at that time only those airplanes had
affected cargo configuration for which Boeing was the design approval
holder. The FAA agreed at that time to not require Boeing to develop a
BITE check service bulletin for the Model 737 airplanes because Boeing
had not yet developed a cargo conversion service bulletin or
supplemental type certificate (STC) for the Model 737 airplanes. The
FAA also considered that, because the BITE check instructions already
existed in the Model 737 AMM, a BITE check service bulletin could be
developed quickly at a later date if needed. In addition, the process
for obtaining FAA agreement on a list of nondispatchable fault codes
for the models Boeing chose to support took less than 30 days. If any
service information is developed to support compliance with paragraph
(h) of this AD it will be evaluated for approval using the AMOC process
specified in paragraph (i) of this AD.

Request To Clarify Required Modification

ANA and Thomson Airways requested that the FAA provide
clarification regarding how to accomplish the modification specified in
paragraph (g) of the proposed AD. ANA noted that paragraph (h) of the
proposed AD provides clear alternative actions for cargo airplanes. ANA
stated that it could not identify how to modify the FQIS in passenger
airplanes not subject to the FTFR rule. ANA noted that it contacted
Boeing for clarification and Boeing stated that the FRM (which Boeing
calls NGS) retrofit is the method of compliance for these airplanes.
ANA asked that the FAA either clarify how to modify the FQIS system or
accept an FRM retrofit as terminating action. Thomson Airways asked if
the intent of the proposed AD is to install an NGS on affected
airplanes. Thomson Airways also asked for clarification regarding the
FQIS modification, stating that the proposed AD does not provide detail
regarding modifying the FQIS itself, only the FQIS wiring.
The FAA agrees to clarify. As noted in paragraph (c) of this AD,
airplanes on which FRM or IMM that meets certain FAA airworthiness
standards is installed are excluded from this AD. Paragraph (g) of this
AD requires modification of the FQIS on passenger airplanes to prevent
development of an ignition source inside the center fuel tank due to
electrical fault conditions. The specifics of this modification may
vary as long as the modification addresses the unsafe condition
identified in this AD and the procedures specified in paragraph (i) of
this AD are used to approve the modification method. Operators may
choose to install an FRM or IMM that meets the criteria specified in
paragraph (c), which would then remove that airplane from the
applicability of this AD, negating the need to do the modification
specified in paragraph (g) of this AD. Otherwise, operators must obtain
an AMOC as specified in paragraph (i) of this AD and modify their
airplane accordingly. The FAA has not changed this AD regarding this
issue.

Request To Provide a Detailed Cost-Effective Method of Compliance

Korean Air Lines (KAL), KLM, AMES CAMO, and Duco Schiere requested
that the FAA provide a detailed and cost-effective method of compliance
for passenger airplanes. KAL, AMES CAMO, and Duco Schiere noted that
the proposed AD does not provide a clear means of compliance for the
modification, such as a Boeing service bulletin. AMES CAMO noted that
without a clear method of compliance, it is difficult to determine the
extent of the required work. KAL and KLM noted that the majority of
non-FAA operators are not required to retrofit the NGS system. KLM
stated that since 2008 the level of fuel tank safety has been improved
by the implementation of several costly SFAR 88 service bulletins,
implementation of airworthiness limitations into the maintenance
program and implementation of CDCCLs into maintenance documents. KLM
mentioned that the modification would require an airplane to be out of
service for a lengthy time. KLM added that the modification would add
weight to the airplane and require additional fuel usage. KAL and KLM
requested that the FAA encourage Boeing to develop an acceptable cost-
effective method of compliance that does not require installation of an
NGS.
The FAA agrees that the lack of service information for FQIS
modifications makes it difficult to assess the required work to modify
the FQIS, and acknowledges the high cost of NGS. However, the FAA
disagrees with the commenters' requests. For passenger-carrying
airplanes, the cost per airplane of providing a modification of the
FQIS that fully complies with the airworthiness standards was estimated
by Boeing and their FQIS vendor (Goodrich) prior to the issuance of the
NPRM to be comparable to the cost of installing NGS. Based on that cost
estimate, Boeing proposed that they not be required to develop a fully
compliant FQIS modification for passenger airplanes because it would
not provide significant savings to operators and NGS would provide a
greater safety benefit. The FAA agreed.
The FAA's understanding is that Boeing's current position is the
same, and that they do not plan to develop a fully compliant FQIS
modification for passenger airplanes to address paragraph (g) of this
AD. However, if service information is developed, approved, and
available in the future, operators may request approval under the
provisions of paragraph (i) of this AD to use approved service
instructions as an AMOC for the requirements of this AD, or the FAA may
approve the service information as a global AMOC for this AD.

Request To Clarify Intent of Different Requirements in Paragraphs (g)
and (h) of the Proposed AD


Boeing asked that the FAA clarify the intent of the differences
between the requirements in paragraphs (g) and (h) of the proposed AD.
Boeing stated that it is unclear what change is expected for compliance
with paragraph (g) of the proposed AD versus paragraph (h) of the
proposed AD. Boeing suggested that one possibility is that paragraph
(g) of the proposed AD is intended to cover development of transient
suppression, while paragraph (h) of the proposed AD is intended to
cover compliance via FQIS wire separation and BITE checks.
The FAA agrees to clarify. Paragraph (g) of this AD is intended to
require, for passenger airplanes that are subject to this AD, a
modification to the FQIS that makes it fully compliant with 14 CFR
25.981(a), as amended by amendment 25-102. A fully compliant FQIS
modification might include wire separation or transient suppression
devices, but due to the system design, either option would likely
require changes to the FQIS processor.
Paragraph (h) of this AD is intended to allow, as an optional
method of compliance for all-cargo airplanes only, a change that
isolates the center fuel tank circuit wiring between the FQIS processor
and the fuel tanks from other wiring that is connected to a sufficient
power source to create an ignition source in the event of a hot short
between the wiring. Such a change would not be fully compliant with the
airworthiness regulations (hence the requirement to obtain a partial
exemption from 14 CFR 25.901(c) and 14 CFR 25.981(a) for any such
design change), but would provide a level of risk reduction that the
FAA considers acceptable for all-cargo airplanes and would
significantly reduce the costs relative to a fully compliant
modification.

Request To Change Compliance Time

A4A/CAA and Thomson Airways requested that the FAA extend the
compliance time for the modifications specified in paragraphs (g) and
(h)(2) of the proposed AD to 72 months. A4A/CAA stated that the
compliance time should match that of AD 2016-07-07 because the unsafe
condition and corrective actions are similar. A4A/CAA stated that
although service information was not yet available, the compliance time
should align with major maintenance schedules, but should be not less
than 72 months after service information is available. Thomson Airways
noted that 72 months would provide operators a better opportunity to
work within existing maintenance program schedules.
Conversely, NATCA recommended that the FAA reject requests for a
compliance time longer than 5 years as proposed in the NPRM. Assuming
final rule issuance in 2016, NATCA estimated that a 5-year compliance
time would result in required compliance by 2021-25 years after the TWA
Flight 800 fuel tank explosion that led to the requirements in SFAR 88,
and 20 years after issuance of SFAR 88.
The FAA agrees with Thomson Airways and A4A/CAA's request to extend
the compliance time, and disagrees with NATCA's request. The FAA
received similar requests to extend the compliance time from several
commenters regarding the NPRMs for the FQIS modification on other
airplanes. The FAA disagrees with establishing a compliance time based
on issuance of any service information that is not yet approved or
available. The FAA has determined that a 72-month compliance time is
appropriate and will provide operators adequate time to prepare for and
perform the required modifications without excessive disruption of
operations. The FAA has determined that the requested moderate increase
in compliance time will continue to provide an acceptable level of
safety. The FAA has changed paragraphs (g) and (h)(2) of this AD
accordingly.

Request To Change Compliance Time Relative to Receipt of Exemption

Boeing requested that the FAA revise the compliance time for the
proposed AD to ``60 months after an exemption from [14 CFR
25.981(a)(3)] is FAA-approved.'' Boeing suggested that it would take 6
months to develop an exemption petition and 6 months for the FAA to
approve that exemption. Boeing added that the FAA has previously identified
that the BITE checks procedure and wire separation design were not
sufficient for compliance with 14 CFR 25.981(a)(3).
The FAA disagrees with the commenter's request. An AD typically
does not include a compliance time that is based on an optional action
that an operator or manufacturer might choose to take. In addition, the
FAA notes that Boeing has already received exemptions for the Model
747-400, 757, and 767 airplanes, and could quickly petition for and
obtain approval of a similar exemption for the Model 737 airplanes
using an almost identical petition. The FAA's flow time to disposition
such a petition would be approximately 90 days, during which time
Boeing could still proceed with development of the modification. In
addition, as noted above, the compliance time for paragraph (h)(2) of
this AD has been extended to 72 months, giving additional time for
operators or manufacturers to obtain an exemption.

Request To Extend Repetitive BITE Check Interval

Boeing requested that paragraph (h)(1) of the proposed AD be
revised to extend the repetitive check interval for the BITE checks.
Boeing requested that the repetitive interval be extended to 750 flight
hours to match the repetitive intervals specified in the service
information for a related AD.
The FAA agrees for the reason provided, and because 750 flight
hours better aligns with most operators' maintenance programs. The FAA
intended to propose a 750 flight hour interval, but inadvertently
specified 650 flight hour intervals in the proposed AD. The FAA has
revised paragraph (h)(1) of this AD to specify repetitive intervals of
750 flight hours.

Request To Revise Costs of Compliance Section To Account for Cargo
Conversions


A4A/CAA noted that the Costs of Compliance section in the NPRM
stated all U.S.-registered airplanes are currently operated as
passenger airplanes and that ``because of the requirement in 14 CFR
121.1117 to install FRM on U.S. air-carrier passenger airplanes by the
end of 2017, it is likely that no U.S. airplanes would actually be
affected by this proposed AD.'' A4A/CAA noted that 14 CFR 121.1117 does
not require FRM to be installed on all-cargo airplanes. The commenter
stated that U.S.-registered Model 737-700 all-cargo airplanes without
FRM installed will be operated by 2017. The FAA infers that A4A/CAA is
requesting that the Costs of Compliance section be revised to reflect
the number of all-cargo U.S.-registered airplanes.
The FAA agrees that there are currently U.S.-registered Model 737-
700 all-cargo airplanes operating without FRM installed. The FAA has
revised the Costs of Compliance section of this AD to reflect these
airplanes.

Request To Acknowledge Impacts on Intrastate Aviation in Alaska

A4A/CAA stated that the proposed AD will interrupt aviation
transportation to remote Alaskan communities not serviced by other
modes of transportation, contrary to the statement that the proposed AD
``will not affect intrastate aviation in Alaska.'' A4A/CAA noted that,
beginning in 2017, Model 737-700 airplanes in an all-cargo
configuration and without FRM installed will provide transportation to
remote Alaskan communities. A4A/CAA added that these airplanes would be
required to be removed from service for an extended time while
accomplishing the proposed modification, which the FAA estimates would
take 1,200 work-hours.
The FAA acknowledges that, since the NPRM was issued, at least one
major operator began using converted Model 737-700 cargo airplanes for
intrastate flights in Alaska. The few remote communities in Alaska that
have airports suitable for a Model 737-700 are unlikely to be served
solely by Model 737-700 airplanes. The FAA has considered the potential
for impact to these communities due to Model 737-700 airplanes being
temporarily out of service for the required modification actions, and
considers the safety concern to outweigh those potential impacts. This
AD was developed with regard to minimizing the economic impact on
operators to the extent possible, consistent with the safety objectives
of this AD. In any event, the Federal Aviation Regulations (14 CFR part
39) require operators to correct an unsafe condition identified on an
airplane to ensure operation of that airplane in an airworthy
condition. The FAA has determined in this case that the requirements
are necessary and the indirect costs would be outweighed by the safety
benefits of the AD. The FAA considers the 72 month compliance adequate
time for operators to schedule the required modifications without
excessive disruption of service to those communities. However, if an
operator considers that a moderate delay in the incorporation of the
required modification would significantly reduce the impact on their
operations or the impact on service to a remote community in Alaska
while still providing an acceptable level of safety, that operator can
use the procedures in paragraph (i) of this AD to explain those impacts
and request approval of an extension of the compliance time.

Request To Require Design Changes From Manufacturers

NATCA recommended that the FAA follow the agency's compliance and
enforcement policy to require manufacturers to develop the necessary
design changes soon enough to support operators' ability to comply with
the proposed requirements. NATCA noted that SFAR 88 required
manufacturers to develop all design changes for unsafe conditions
identified by their SFAR 88 design reviews by December 2002, or within
an additional 18 months if the FAA granted an extension.
The FAA acknowledges the commenter's concerns. However, any
enforcement action is outside the scope of this rulemaking. The FAA has
not changed this final rule regarding this issue.

Request To Clarify the Applicability

Duco Schiere stated the NPRM is not clear about which
configurations (passenger/cargo, with/without NGS installed) of Model
737 airplanes are applicable to the AD. The FAA infers the commenter is
requesting the FAA clarify the applicability.
The FAA agrees to clarify. This AD applies to The Boeing Company
Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes
(including passenger and cargo airplanes) except for airplanes having
configurations identified in paragraphs (c)(1) and (2) of this AD.
Airplanes with an installed NGS that meets the criteria specified in
paragraph (c)(1) of this AD are excluded from this AD. Airplanes with
an installed IMM such as fuel tank explosion suppression foam that
meets the criteria specified in paragraph (c)(2) of this AD are also
excluded from this AD.

Clarification of BITE Check Compliance Time

The FAA has revised paragraph (h)(1) of this AD to clarify the
compliance time for the BITE check relative to the requirement to
record the fault codes. The FAA recognized that operators might
interpret the proposed requirements for alternative actions for cargo
airplanes as allowing additional flights prior to performing the BITE
check after first recording the fault codes. The FAA intended for
operators to perform the BITE check immediately after recording the
fault codes to address both the fault codes that exist prior to performing
the BITE check and any new codes that are identified during the BITE check.

Clarification of Costs of Compliance

The FAA had previously determined, as specified in the NPRM, that
the work involved for the cargo airplane wire separation modification
would take 230 work-hours. Boeing has since provided an updated
estimate of 74 work-hours for the alternative modification for cargo
airplanes. The FAA has revised the cost estimate for the modification
accordingly in this final rule.

Conclusion

The FAA reviewed the relevant data, considered the comments
received, and determined that air safety and the public interest
require adopting this final rule with the changes described previously
and minor editorial changes. The FAA has determined that these minor
changes:
Are consistent with the intent that was proposed in the
NPRM for addressing the unsafe condition; and
Do not add any additional burden upon the public than was
already proposed in the NPRM.
The FAA also determined that these changes will not increase the
economic burden on any operator or increase the scope of this final
rule.

Costs of Compliance

There are approximately 1,393 U.S.-registered Model 737-600, -700,
-700C, -800, -900, and -900ER series airplanes in service. Several of
those airplanes are currently operated as cargo airplanes. Beginning
with line number 2620, however, Boeing has delivered airplanes with
FRM/NGS installed. The FAA estimates that 831 affected airplanes on the
U.S. Register were delivered without FRM installed, but the agency does
not know the number of airplanes that have had FRM installed post-
production. Because of the requirement in 14 CFR 121.1117 to install
FRM on U.S. air-carrier passenger airplanes by the end of 2017, it is
likely that no U.S. passenger airplanes would actually be affected by
this AD. However, U.S.-registered cargo airplanes may be affected by
this AD. For any affected airplane, the FAA estimates the following
costs to comply with this AD:

Estimated Costs: Required Actions

Action
Labor cost
Parts cost
Cost per product
Modification 1,200 work-hours x $85 per hour = $102,000
$200,000
$302,000

Estimated Costs: Alternative Actions

Action
Labor cost
Parts cost
Cost per product
BITE check 1 work-hour x $85 per hour = $85 per check $0 $85 per check (4 checks per year, $340 per year)
Wire separation 74 work-hours x $85 per hour = $6,290 10,000 16,290

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.
The FAA is 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

This AD will not have federalism implications under Executive Order
13132. This AD will 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 that this AD:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Will not affect intrastate aviation in Alaska, and
(3) 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.

Adoption of the Amendment

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

PART 39--AIRWORTHINESS DIRECTIVES

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]

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