[Federal Register Volume 63, Number 77 (Wednesday, April 22, 1998)]
[Proposed Rules]
[Pages 19852-19854]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-10590]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-50-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, 
and -500 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to all Boeing Model 737-100, -200, -
300, -400, and -500 series airplanes. This proposal would require 
installation of components for the suppression of electrical 
transients, and/or installation of components to provide shielding and 
separation to the fuel system wiring that is routed to the fuel tanks 
from adjacent wiring. The proposal also would require installation of 
flame arrestors and pressure relief valves in the fuel vent system. 
This proposal is prompted by testing results, obtained in support of an 
accident investigation, and by re-examination of possible causes of a 
similar accident. The actions specified by the proposed AD are intended 
to prevent possible ignition of fuel vapors in the fuel tanks, and 
external ignition of the fuel vapor exiting the fuel vent system and 
consequent propagation of a flame front into the fuel tanks.

DATES: Comments must be received by June 8, 1998.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-50-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal 
holidays.

FOR FURTHER INFORMATION CONTACT: Chris Hartonas, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, telephone (425) 227-2864; or 
Dorr Anderson, Aerospace Engineer, Propulsion Branch, ANM-140S, 
telephone (425) 227-2684; FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address

[[Page 19853]]

specified above. All communications received on or before the closing 
date for comments, specified above, will be considered before taking 
action on the proposed rule. The proposals contained in this notice may 
be changed in light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 98-NM-50-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 98-NM-50-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On July 17, 1996, a Boeing Model 747 series airplane was involved 
in an accident shortly after takeoff from John F. Kennedy International 
Airport in Jamaica, New York. In support of the subsequent accident 
investigation, the FAA participated in testing of the fuel quantity 
indication system (FQIS). Results of that testing revealed that higher 
than expected energy levels could be induced by high transient voltage 
levels in the electrical wiring and probes of the fuel system. These 
energy levels occurred when the wiring of the FQIS was subjected to 
electromagnetic interference (EMI) testing. EMI or electrical 
transients may be generated in the airplane when switching electrical 
loads in the wiring adjacent to the FQIS wiring.
    As part of this testing, conductive debris, such as steel wool and 
lockwire, was used to bridge the FQIS probes to simulate debris that 
has been found in fuel tanks during inspections of transport category 
airplanes. Results of the tests indicated that higher than expected 
transient voltage levels in the FQIS wiring and probes could be 
induced, and the resulting energy levels in the FQIS wiring and probes 
could be greater than the energy required to ignite fuel vapor inside a 
fuel tank.
    In addition, recent inspections of the fuel probe wiring in Model 
747 fuel tanks revealed damaged wiring insulation, which exposed the 
conductors inside the fuel tanks. This condition, together with the 
introduction of induced transients or short circuit conditions, may 
result in potential ignition sources in a fuel tank.
    Although the testing and inspections evaluated FQIS wiring, the 
same conditions can be generated with other wiring that is routed to 
the fuel tanks. The conditions described above, if not corrected, could 
result in excessive levels of energy in fuel system wiring that is 
routed to the fuel tanks and a potential source of ignition in the fuel 
tanks.
    The fuel system wire installation on Model 737-100, -200, -300, -
400, and -500 series airplanes is similar to that on the Model 747 
series airplane involved in the 1996 accident. Therefore, those Model 
737-100, -200, -300, -400, and -500 series airplanes may be subject to 
the same unsafe condition revealed on the Model 747-100, -200, and -300 
series airplanes.
    The accident investigation has included a review of previous fuel 
tank explosions, including a Model 737-300 series airplane accident on 
May 11, 1990, in the Philippines. One possible scenario which may have 
caused the 1990 accident is an external ignition of the fuel vapor 
exiting the fuel vent system and consequent propagation of a flame 
front into the wingtip vent scoop and through the vent system into the 
center tank. The Model 737-300 vent system does not include flame 
arrestors and pressure relief valves and would allow a flame front to 
travel unimpeded into the vent system through the wingtip vent scoop. 
The conditions described above, if not corrected, could result in a 
potential source of ignition in a fuel tank.
    The fuel vent system on Model 737-100, -200, -400, and -500 series 
airplanes is identical to that on the Model 737-300 series airplane. 
Therefore, those Model 737-100, -200, -400, and -500 series airplanes 
may be subject to the same unsafe condition revealed on the Model 737-
300 series airplanes.

FAA's Conclusions

    While none of the above conditions have been identified at this 
time as the cause of the accidents discussed previously, the FAA 
concludes that results of the tests and inspections that have been 
performed indicate that modifications are required to limit the energy 
level induced in the fuel system wiring and FQIS probes. Furthermore, 
the FAA has determined that installation of components for the 
suppression of electrical transients, and/or installation of components 
to provide shielding and separation to the fuel system wiring that is 
routed to the fuel tanks from adjacent wiring is necessary to provide 
protection from wire-to-wire electrical short circuit conditions. Such 
conditions are a potential source of ignition in the fuel tanks. In 
addition, the FAA has determined that installation of flame arrestors 
and pressure relief valves in the fuel vent system is necessary to 
prevent a flame front from propagating through the fuel vent system and 
igniting vapors present in the fuel tanks.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require installation of components for the 
suppression of electrical transients, and/or installation of components 
to provide shielding and separation of the fuel system wiring that is 
routed to the fuel tanks from adjacent wiring. The proposed AD also 
would require installation of flame arrestors and pressure relief 
valves in the fuel vent system. The actions would be required to be 
accomplished in accordance with a method approved by the FAA.

Cost Impact

    There are approximately 2,781 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 1,140 airplanes of U.S. 
registry would be affected by this proposed AD.
    Since the manufacturer has not yet developed a modification 
commensurate with the requirements of this proposal, the FAA is unable 
at this time to provide specific information as to the number of work 
hours or the cost of parts that would be required to accomplish the 
proposed modifications. A further problem in developing a specific cost 
estimate is the fact that proposed modification costs are expected to 
vary from operator to operator and from airplane to airplane depending 
upon airplane configuration. The proposed compliance time of 12 months 
should provide ample time for the development, approval, and 
installation of an appropriate modification.
    However, based on similar modifications accomplished previously on 
other airplane models, the FAA can reasonably estimate that the 
proposed

[[Page 19854]]

modification to the fuel system wiring would require 40 work hours to 
accomplish, at an average labor rate of $60 per work hour. The cost of 
required parts is estimated to be $10,000 per airplane. Based on these 
figures, the cost impact of this proposed modification on U.S. 
operators is estimated to be $14,136,000, or $12,400 per airplane.
    In addition, based on similar modifications accomplished previously 
on other airplane models, the FAA can reasonably estimate that the 
proposed modification to the fuel vent system would require 48 work 
hours to accomplish, at an average labor rate of $60 per work hour. The 
cost of required parts is estimated to be $20,400 per airplane. Based 
on these figures, the cost impact of this proposed modification on U.S. 
operators is estimated to be $26,539,200, or $23,280 per airplane.
    As indicated earlier in this preamble, the FAA specifically invites 
the submission of comments and other data regarding the economic aspect 
of this proposal.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would not have substantial direct 
effects 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. Therefore, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, 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. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (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. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: Docket 98-NM-50-AD.

    Applicability: All Model 737-100, -200, -300, -400, and -500 
series airplanes, certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (c) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent possible ignition of fuel vapors in the fuel tanks, 
and/or external ignition of the fuel vapor exiting the fuel vent 
system and subsequent propagation of a flame front into the fuel 
tanks, accomplish the following:
    (a) Within 12 months after the effective date of this AD, 
install components for the suppression of electrical transients, 
and/or install components to provide shielding and separation to the 
fuel system wiring that is routed to the fuel tanks from adjacent 
wiring, in accordance with a method approved by the Manager, Seattle 
Aircraft Certification Office (ACO), FAA, Transport Airplane 
Directorate.
    (b) Within 12 months after the effective date of this AD, 
install flame arrestors and pressure relief valves in the fuel vent 
system, in accordance with a method approved by the Manager, Seattle 
ACO.
    (c) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle ACO. Operators shall submit 
their requests through an appropriate FAA Principal Maintenance 
Inspector, who may add comments and then send it to the Manager, 
Seattle ACO.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (d) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on April 14, 1998.
John J. Hickey,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-10590 Filed 4-21-98; 8:45 am]
BILLING CODE 4910-13-U