[Federal Register Volume 85, Number 29 (Wednesday, February 12, 2020)]
[Rules and Regulations]
[Pages 7868-7871]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-02667]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2016-9073; Product Identifier 2015-NM-062-AD; Amendment 
39-19836; AD 2020-03-11]
RIN 2120-AA64


Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for 
certain Boeing Model 707 airplanes and Model 720 and 720B series 
airplanes. This AD was prompted by the FAA's analysis of the Model 707 
and 720 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. The FAA is issuing this AD to 
address the unsafe condition on these products.

DATES: This AD is effective March 18, 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-
9073; 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

[[Page 7869]]

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: 
[email protected].

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 Boeing Model 
707 airplanes and Model 720 and 720B series airplanes. The NPRM 
published in the Federal Register on September 23, 2016 (81 FR 65577). 
The NPRM was prompted by the FAA's analysis of the Model 707 and 720 
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 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.

Request To Withdraw NPRM: No Unsafe Condition

    Boeing requested that the FAA withdraw the NPRM. Boeing reported 
that its safety analysis indicated that the FQIS on the Model 707/720 
airplane does not have an unsafe condition. Boeing noted that three 
fuel-tank safety-related actions, including changes to the lightning 
shielding of the FQIS wires in the wing leading edge area, are required 
by AD 2007-23-12, Amendment 39-15258 (72 FR 63800, November 13, 2007; 
corrected January 10, 2008 (73 FR 1816)) (``AD 2007-23-12''). Boeing 
pointed out that AD 2007-23-12 requires operators to perform a survey 
of the fuel system wiring configurations on its airplanes. (That AD 
also requires operators to report the results of the surveys and 
discrepancies found.) Boeing stated that no operator has reported any 
discrepancy, and no operator has requested service information to 
support any changes related to fuel tank safety.
    The FAA disagrees with the commenter's 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 to 
part 25. At the time of the unsafe condition determination in April 
2003, Boeing acknowledged that the Model 707/720 center fuel tank was a 
high-flammability fuel tank. The Boeing SFAR 88 report for the Model 
707/720 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 memorandum 
due to the similarity of the Model 707/720 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 addition of lightning shields required by AD 
2007-23-12 is unrelated to the unsafe condition that prompted this AD, 
and was instead driven by a concern that a critical lightning strike 
could cause an ignition source in the tank via FQIS wiring. The FAA has 
therefore determined that it is necessary to issue this final rule as 
proposed.
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    \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.
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Request To Withdraw NPRM: No Passenger Airplanes Affected

    Boeing requested that the FAA withdraw the NPRM because none of the 
four affected U.S.-registered airplanes are passenger airplanes, and 
the world fleet size and fleet operational exposure for these airplanes 
continue to decline with time. Boeing stated that its safety 
assessment, using methodologies ``recognized by the FAA,'' shows that 
the vulnerability of the Model 707/720 FQIS to a latent failure plus a 
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 commenter's request. The FAA has not 
limited its actions related to fuel tank safety to passenger airplanes. 
The FAA has determined that an unsafe condition exists using the 
decision criteria in FAA Policy Memorandum PS-ANMl00-2003-112-15. The 
FAA assumes that in citing assessment methodologies recognized by the 
FAA, Boeing is referring to having performed an assessment of the total 
fleet risk for the Model 707/720 fleet that showed a very low 
likelihood of a fuel tank ignition event in the remaining life of that 
fleet. However the FAA's unsafe condition determination was calculated 
using the decision criteria in FAA Policy Memorandum ANMl00-2003-112-
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. That 
combination of failures was classified as a ``known combination of 
failures'' under the criteria in the policy memo due to the similarity 
of the Model 707/720 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 is expected to be similar to the cost of the actions 
required for Model 737 and 747 airplanes in AD 99-03-04, Amendment

[[Page 7870]]

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''). Therefore, the FAA has made no changes to 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 707/720 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 commenter's 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 707/720 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 707/720 
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. Therefore, the FAA has made no changes to this final 
rule as a result of this comment.

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 a design solution 
for the center wing tank FQIS. Boeing expected that a small number of 
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 actual modifications for 
which they provided cost comments.
    The FAA disagrees with the commenter's request to revise the cost 
estimate. The FAA based the cost estimate for Model 707/720 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 707/720 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. 
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 one affected U.S. passenger airplane in operation at the 
time the NPRM was published has been removed from service. The 
remaining U.S. airplanes are an experimental research airplane and 
privately owned military contract aerial refuelers. For those 
airplanes, the operators have the potential to use the Alternative 
Methods of Compliance (AMOC) approval process to propose alternative 
approaches to address the unsafe condition using operational or 
utilization restrictions. The FAA has made no changes to this final 
rule as a result of this comment.

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 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 three airplanes of U.S. 
registry: two cargo/tanker airplanes and one experimental airplane. The 
FAA estimates the following costs to comply with this AD:

                                      Estimated Costs for Required Actions
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                                                                                     Cost per      Cost on U.S.
                Action                         Labor cost           Parts  cost       product        operators
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Modification..........................  600 work-hours x $85 per        $150,000        $201,000        $603,000
                                         hour = $51,000.
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[[Page 7871]]

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

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):

2020-03-11 The Boeing Company: Amendment 39-19836; Docket No. FAA-
2016-9073; Product Identifier 2015-NM-062-AD.

(a) Effective Date

    This AD is effective March 18, 2020.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to The Boeing Company Model 707-100 long body, -
200, -100B long body, -100B short body, -300, -300B, -300C, and -400 
series airplanes; and Model 720 and 720B series airplanes; 
certificated in any category; excluding 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 14 CFR 26.33(c)(1).

(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 707/720 
fuel system reviews conducted by the manufacturer. 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.

(f) Compliance

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

(g) Modification

    Within 60 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 (h) of this AD.

(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: [email protected].
    (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: [email protected].

(j) Material Incorporated by Reference

    None.

    Issued on February 3, 2020.
Lance T. Gant,
Director, Compliance & Airworthiness Division, Aircraft Certification 
Service.
[FR Doc. 2020-02667 Filed 2-11-20; 8:45 am]
BILLING CODE 4910-13-P