Document ID: FAA-2016-9072-0007
Agency: faa
Document Type: Rule
Title: Airworthiness Directives: The Boeing Company Airplanes
Posted Date: 2019-12-31T05:00Z

[Federal Register Volume 84, Number 250 (Tuesday, December 31, 2019)]
[Rules and Regulations]
[Pages 72227-72230]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2019-27885]

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 Rules and Regulations
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  Federal Register / Vol. 84, No. 250 / Tuesday, December 31, 2019 / 
Rules and Regulations  

[[Page 72227]]

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2016-9072; Product Identifier 2015-NM-110-AD; Amendment 
39-19797; AD 2019-23-04]
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 727 airplanes. This AD was prompted by 
the FAA's analysis of the Model 727 fuel system review conducted by the 
manufacturer. This AD requires modifying the fuel quantity indicating 
system (FQIS) to prevent development of an ignition source inside the 
body-mounted auxiliary fuel tanks due to electrical fault conditions. 
As an alternative to the modification, this AD allows deactivating the 
body-mounted auxiliary fuel tanks. The FAA is issuing this AD to 
address the unsafe condition on these products.

DATES: This AD is effective February 4, 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-
9072; 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, the regulatory evaluation, 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:

Background

    The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 
CFR part 39 by adding an AD that would apply to certain Boeing Model 
727 airplanes equipped with Boeing body-mounted auxiliary fuel tanks. 
The NPRM published in the Federal Register on September 23, 2016 (81 FR 
65579). The NPRM was prompted by the FAA's analysis of the Model 727 
fuel system review conducted by the manufacturer. The NPRM proposed to 
require modifying the FQIS to prevent development of an ignition source 
inside the body-mounted auxiliary fuel tanks due to electrical fault 
conditions. As an alternative to the modification, the NPRM proposed to 
allow deactivating the body-mounted auxiliary fuel tanks.
    The FAA is issuing this AD to address ignition sources inside the 
body-mounted auxiliary fuel tanks, 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.

Request To Withdraw NPRM: No Unsafe Condition

    Boeing requested that the FAA withdraw the NPRM. Boeing reported 
that its system safety assessment determined that the FQIS on the Model 
727 airplane does not have an unsafe condition.
    The FAA disagrees with the request. Boeing did not provide specific 
details about the type of assessment that was performed (total fleet 
risk, average risk per flight hour, peak individual flight risk, etc.). 
Based on Boeing's fuel system safety assessment submitted in response 
to Special Federal Aviation Regulation No. 88 (``SFAR 88'') of 14 CFR 
part 21, the FAA has determined that there is an unsafe condition due 
to the potential for a fuel tank ignition source to occur from the FQIS 
due to its design architecture, component design details, and 
installation design details. The FAA's determination was made in 
accordance with the guidance contained in FAA Policy Memorandum ANM100-
2003-112-15, ``SFAR 88--Mandatory Action Decision Criteria,'' dated 
February 25, 2003.\1\ Under that policy, an ignition source that can 
occur in a high-flammability fuel tank, due to a combination of a 
preexisting failure that can exist undetected for multiple flights and 
one additional failure, is an unsafe condition requiring corrective 
action. High-flammability fuel tanks are defined in the policy as fuel 
tanks with a fleet average flammability greater than 7 percent as 
calculated in accordance with 14 CFR Appendix N of part 25. At the time 
of the unsafe condition determination in April 2003, Boeing 
acknowledged that the Model 727 body-mounted auxiliary fuel tanks are 
high-flammability fuel tanks. The Boeing SFAR 88 report for the Model 
727 showed that a combination of an in-tank wire fault or contamination 
condition (which can remain latent for multiple flights) and a hot 
short outside of the tank between the affected FQIS tank circuit and 
other aircraft power wiring cobundled with FQIS tank circuit wiring 
could result in an ignition source in the fuel tank. That combination 
of failures was classified by the FAA as a ``known combination of 
failures'' under the criteria in the policy memo due to the similarity 
of the Model 727 FQIS system architecture and design details to those 
of the Boeing Model 747 airplane involved in the TWA Flight 800 
catastrophic fuel tank explosion accident in 1996. The National 
Transportation Safety Board (NTSB) concluded that an FQIS failure 
combination as described above was the most likely cause of that 
accident.\2\ The FAA has therefore determined that it is necessary to 
issue this final rule.
---------------------------------------------------------------------------

    \1\ http://rgl.faa.gov/Regulatory_and_Guidance_Library/
rgPolicy.nsf/0/dc94c3a46396950386256d5e006aed11/$FILE/Feb2503.pdf.
    \2\ NTSB Aviation Accident Report AAR-00-03 https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0003.pdf.

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

[[Page 72228]]

Request To Withdraw NPRM: Limited Vulnerability to Unsafe Condition

    Boeing requested that the FAA withdraw the NPRM. Boeing stated that 
272 airplanes were manufactured with body-mounted auxiliary fuel tanks, 
but only six were operated under FAA jurisdiction when the comment was 
submitted, and that the fleet exposure continues to decrease due to 
airplane aging and retirements. Boeing stated that its safety 
assessment, using methodologies ``recognized by the FAA,'' shows that 
the vulnerability of the Model 727 FQIS latent failure plus single 
failure does not present an unsafe condition. Boeing concluded that 
requiring the proposed actions will not promote air safety and instead 
will add unnecessary cost to operators.
    The FAA disagrees with the request. The FAA has determined that an 
unsafe condition exists. The FAA assumes that, in citing assessment 
methodologies recognized by the FAA, Boeing is referring to having 
performed its assessment of the total fleet risk for the Model 727 
fleet that showed a very low likelihood of a fuel tank ignition event 
in the remaining life of that fleet. Boeing mentioned the number of 
airplanes operated under U.S. jurisdiction. The FAA, as the civil 
aviation authority of the state of design, is obligated, under the 
Convention on International Civil Aviation (the Treaty), to inform all 
affected aircraft of continuing safety issues regardless of where they 
are operated. Issuance of airworthiness directives is the accepted 
method by which the FAA notifies aviation authorities of other 
countries of an unsafe condition as required by Annex 8 of the Treaty.
    The FAA's unsafe condition determination was made using the 
decision criteria in FAA Policy Memorandum ANM100-2003-112-15. This 
determination was not driven by a fleet risk assessment. A latent in-
tank failure that provides a conductive path or reduces dielectric 
strength of the tank wiring or components, combined with an external 
wiring system failure that conducts power onto the tank wiring, could 
create an ignition source in the fuel tank of the Boeing Model 727 
airplane. That combination of failures was classified as a ``known 
combination of failures'' under the criteria in the policy memorandum 
due to the similarity of the Model 727 FQIS system architecture and 
design details to those of the Model 747 airplane involved in the 
catastrophic fuel tank explosion. The NTSB concluded that an FQIS 
failure combination as described above was the most likely cause of 
that accident. The FAA therefore considers it necessary to address this 
unsafe condition. The per-airplane cost for modification is expected to 
be approximately the same as the cost of the similar actions required 
for Model 737 and 747 airplanes specified in AD 99-03-04, Amendment 39-
11018 (64 FR 4959, February 2, 1999) (``AD 99-03-04''); and AD 98-20-
40, Amendment 39-10808 (63 FR 52147, September 30, 1998) (``AD 98-20-
40''). If an operator chooses to deactivate or remove the auxiliary 
tanks as allowed by the AD, the cost would be significantly lower. 
Therefore, the FAA made no changes in this final rule as a result of 
this comment.

Request To Withdraw NPRM: Extremely Remote Likelihood of Unsafe 
Condition

    Boeing requested that the FAA withdraw the NPRM. Boeing considered 
the likelihood of an undetected latent electrical fault condition of 
the FQIS to be extremely remote, due to the FQIS architecture. Boeing 
added that the existing Model 727 FQIS design uses a three-wire system 
that goes directly from the fuel tank to the flight deck indication. 
Boeing stated that an electrical fault of an in-tank component causes 
the FQIS to provide a fault indication to the flight crew, so the 
failure is not latent.
    The FAA disagrees with the request. The agency contacted Boeing to 
resolve the apparent conflict between this comment and the company's 
previously submitted SFAR 88 reports. In the SFAR 88 reports for Model 
727 airplanes, Boeing stated that a latent in-tank failure condition 
could not be claimed to be extremely remote, and acknowledged that the 
system does not comply with the requirements of 14 CFR 25.981(a)(3) 
related to a latent failure plus a single failure. (Extremely remote 
qualitatively means that the condition would occur no more than a few 
times in the total fleet life. In numerical probability analysis, a 
condition that has a probability on the order of 1 in 10 million flight 
hours or less is considered extremely remote.) However, the comment 
that Boeing submitted to the NPRM stated that a latent in-tank failure 
was extremely remote.
    A meeting with representatives from the FAA and Boeing was held 
February 15, 2019, to clarify Boeing's position. (A record of that 
meeting has been posted to the AD docket.) Boeing explained that it had 
intended to convey in its comment that the estimated probability for 
the initial failure that creates a latent in-tank loss of dielectric 
strength, resistive current path, or short condition is extremely 
remote. Boeing acknowledged that when the estimated probability of that 
failure initiation is multiplied by the average latency period, the 
probability of a latent in-tank failure existing in any given flight 
hour is not extremely remote.
    Given this clarification, Boeing's comment was consistent with the 
conclusions of its SFAR 88 reviews. The FQIS does not provide a fault 
indication to the flight crew other than unusual readings or a zero 
reading provided by a tank gage if a hard short to ground or power 
occurs. In addition, even if such a fault is noted by the flight crew, 
the approved Master Minimum Equipment List for the Model 727 airplane 
allows operators to fly for up to ten days in that condition, without 
disconnecting the FQIS for the affected tank, with provisions for 
extending beyond the ten days. The FAA therefore does not agree that a 
latent failure of in-tank wiring or components, such that an ignition 
source could occur if an external hot short occurs, is extremely 
remote. No changes were made to this final rule as a result of this 
comment.

Request To Extend Compliance Time

    Boeing requested that the FAA revise the proposed 12-month 
compliance time, which it asserts will require Model 727 operators to 
``develop the solution on their own (under 14 CFR part 121).'' Boeing 
stated that it had no plans to create service action to modify the FQIS 
or deactivate the auxiliary tank(s), as no operators have contacted 
Boeing requesting this support.
    The FAA disagrees with the request. Boeing did not propose a 
specific compliance time, and after consideration, the agency still 
considers 12 months to be adequate to allow operators to deactivate 
their auxiliary tanks using existing information in the airplane 
maintenance manual to develop alteration data and obtain FAA approval 
of an alternative method of compliance (AMOC). A compliance time of 12 
months or less is required for the deactivation of other after-market 
body-mounted auxiliary fuel tanks on Model 727 airplanes in other ADs: 
AD 2008-07-07, Amendment 39-15448 (73 FR 15880, March 26, 2008); AD 
2008-07-09, Amendment 39-15450 (73 FR 16515, March 28, 2008); AD 2008-
12-03, Amendment 39-15546 (73 FR 31749, June 4, 2008); and AD 2009-20-
01, Amendment 39-16024 (74 FR 48007, September 21, 2009). The FAA has 
not changed this AD regarding this issue. Under the provisions of 
paragraph (h) of this AD, however, the FAA will consider requests for 
approval of an extension to the compliance time if

[[Page 72229]]

sufficient data are submitted to substantiate that the new compliance 
time would provide an acceptable level of safety.

Request To Revise Cost Estimate

    Boeing requested that if the NPRM is not withdrawn, the FAA revise 
the cost estimate to reflect the cost of developing an FQIS design 
solution for the body-mounted auxiliary tanks. Boeing expected that 
only six airplanes would actually be modified, so the cost of 
developing a design solution would be spread over a small number of 
airplanes, resulting in a significant per-airplane cost. Boeing did not 
provide any specific cost information or describe the modifications for 
which they provided cost comments.
    The FAA disagrees with the request to revise the cost estimate 
based on this comment. The agency based its cost estimate for Model 727 
passenger airplanes on the inflation-adjusted estimated costs for 
installation of transient suppression devices on the Model 747 airplane 
as required by AD 98-20-40. The FAA considers that the transient 
suppression design solutions, if not the actual parts, developed for 
Model 737 and 747 airplanes in response to AD 99-03-04 and AD 98-20-40 
will be applicable to the Model 727 airplane due to the similarity of 
those models' FQIS designs. The FAA agrees that the nonrecurring design 
development costs associated with any necessary model-specific design 
activity will be spread over fewer airplanes, resulting in higher per-
airplane costs if the operator decides not to deactivate the subject 
tanks. However, the FAA increased the cost estimate in the NPRM to 
reflect that increased cost to the existing fleet. Boeing did not 
propose any specific alternative cost figures to be substituted for the 
FAA estimate. The FAA did not change this final rule as a result of 
this comment.

Conclusion

    The FAA reviewed the relevant data as previously discussed, 
considered the comments received, and determined that air safety and 
the public interest require adopting this final rule as proposed, 
except for 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.

Costs of Compliance

    The FAA estimates that this AD affects 6 airplanes of U.S. 
registry. The FAA estimates the following costs to comply with this AD:

                                        Estimated Costs: Required Actions
----------------------------------------------------------------------------------------------------------------
                                                                                    Cost per       Cost on U.S.
               Action                        Labor cost           Parts cost        product         operators
----------------------------------------------------------------------------------------------------------------
Modification........................  300 work-hours x $85           $100,000         $125,500         $753,000
                                       per hour = $25,500.
----------------------------------------------------------------------------------------------------------------

                                      Estimated Costs: Alternative Actions
----------------------------------------------------------------------------------------------------------------
                                                                                                     Cost per
                    Action                                Labor cost               Parts cost        product
----------------------------------------------------------------------------------------------------------------
Tank deactivation............................  10 work-hours x $85 per hour =               $0             $850
                                                $850.
----------------------------------------------------------------------------------------------------------------

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.
    This AD is issued in accordance with authority delegated by the 
Executive Director, Aircraft Certification Service, as authorized by 
FAA Order 8000.51C. In accordance with that order, issuance of ADs is 
normally a function of the Compliance and Airworthiness Division, but 
during this transition period, the Executive Director has delegated the 
authority to issue ADs applicable to transport category airplanes and 
associated appliances to the Director of the System Oversight Division.

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

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):

2019-23-04 The Boeing Company: Amendment 39-19797; Docket No.

[[Page 72230]]

FAA-2016-9072; Product Identifier 2015-NM-110-AD.

(a) Effective Date

    This AD is effective February 4, 2020.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to The Boeing Company Model 727, 727-100, 727C, 
727-100C, 727-200, and 727-200F series airplanes; certificated in 
any category; equipped with Boeing body-mounted auxiliary fuel 
tanks.

(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 727 fuel 
system review conducted by the manufacturer. The FAA is issuing this 
AD to address ignition sources inside the body-mounted auxiliary 
fuel tanks, 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 already done.

(g) Modification

    Within 12 months after the effective date of this AD, do the 
actions specified in either paragraph (g)(1) or (2) of this AD, 
using a method approved in accordance with the procedures specified 
in paragraph (h) of this AD.
    (1) Modify the fuel quantity indicating system (FQIS) to prevent 
development of an ignition source inside the body-mounted auxiliary 
fuel tanks due to electrical fault conditions.
    (2) Deactivate the body-mounted auxiliary fuel tanks.

(h) 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 (i) 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.
    (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, modification deviation, or alteration deviation must meet 
the certification basis of the airplane and the approval must 
specifically refer to this AD.

(i) 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.

(j) Material Incorporated by Reference

    None.

    Issued in Des Moines, Washington, on November 27, 2019.
Michael Kaszycki,
Acting Director, System Oversight Division, Aircraft Certification 
Service.
[FR Doc. 2019-27885 Filed 12-30-19; 8:45 am]
BILLING CODE 4910-13-P