[Federal Register Volume 64, Number 113 (Monday, June 14, 1999)]
[Proposed Rules]
[Pages 31762-31764]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-14934]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-47-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 certain Boeing Model 737-100, -
200, -300, -400, and -500 series airplanes. For certain airplanes, this 
proposal would require installation of a transient suppression diode in 
the wiring circuit of the refueling valve-to-float switch of each fuel 
tank. For certain other airplanes, this proposal would require 
replacement of the existing transient suppression diode with an 
improved diode. This proposal also would require a functional test to 
verify proper installation of each diode, and corrective action, if 
necessary. This proposal is prompted by incidents of electrical fire 
during fueling of the airplane, due to a short circuit and overheating 
of a transient suppression diode. The actions specified by the proposed 
AD are intended to prevent such conditions, which could result in 
electrical arcing and ignition of fuel vapors at the refueling 
receptacle for the fuel tanks, and consequent fire during airplane 
fueling.

DATES: Comments must be received by July 29, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-47-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.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Dorr Anderson, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2684; 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 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 99-NM-47-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. 99-NM-47-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports indicating that electrical fires have 
been detected during fueling of two Boeing Model 737 series airplanes. 
The affected airplanes have transient suppression diodes installed in 
the wiring circuit of the refueling valve-to-float switch of the fuel 
tanks to prevent electrical transients from entering the fuel tanks.
    Investigation revealed that a short circuit in the transient 
suppression diode of the number 1 fuel tank caused electrical arcing, 
and consequent fire. The diode is located 17 inches from the P15 
pressure fueling panel. In the event

[[Page 31763]]

of a short circuit of a transient suppression diode and consequent 
electrical fire, the proximity of the diode to the pressure fueling 
panel could result in ignition of fuel vapors at the fueling receptacle 
during fueling. The fuel valve circuit, of which the diode is part, is 
powered only during pressure fueling on the ground; therefore, the 
diode is most likely to short circuit and overheat during airplane 
fueling.
    Inspection of production diodes by the manufacturer revealed that 
the manufacturing process may be the cause of the failure of the diodes 
during normal operation of the airplane. The failures appear to be 
caused by stresses on the internal leads and end caps of the diode by 
the placement of the wire crimps next to the glass body of the diode. 
The manufacturer replaced the deficient diodes with improved diodes 
during production of Model 737 series airplanes having line numbers 
3017 and subsequent.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 737-28-
1115, dated March 4, 1999, which describes procedures for installation 
of a transient suppression diode in the wiring circuit of the refueling 
valve-to-float switch of each fuel tank on certain airplanes, and 
replacement of the existing transient suppression diode with an 
improved diode, on certain other airplanes. The service bulletin also 
describes procedures for a functional test to verify proper 
installation of each diode. Accomplishment of the actions specified in 
the service bulletin is intended to adequately address the identified 
unsafe condition.

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 accomplishment of the actions specified in 
the service bulletin described previously, except as discussed below.

Differences Between Proposed Rule and Service Bulletin

    Operators should note that, although the service bulletin 
recommends installation of the improved diodes as soon as manpower and 
materials are available, the FAA has determined that a 12-month 
compliance time would address the identified unsafe condition in a 
timely manner. In developing an appropriate compliance time for this 
AD, the FAA considered not only the manufacturer's recommendation, but 
the degree of urgency associated with addressing the subject unsafe 
condition, the average utilization of the affected fleet, and the time 
necessary to perform the modification. In light of all of these 
factors, the FAA finds a 12-month compliance time for completion of the 
proposed replacement to be warranted, in that it represents an 
appropriate interval of time allowable for affected airplanes to 
continue to operate without compromising safety.
    Operators also should note that, although the service bulletin does 
not specify corrective action if any discrepancy is detected during the 
functional test of the transient suppression diode, this proposal would 
require replacement of the discrepant diode to be accomplished in 
accordance with the procedures specified in the service bulletin.

Cost Impact

    There are approximately 2,897 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 1,126 airplanes of U.S. 
registry would be affected by this proposed AD.
    For all airplanes, it would take approximately 7 work hours per 
airplane to accomplish the proposed replacement or installation (as 
applicable), and the functional test to verify proper installation, at 
an average labor rate of $60 per work hour. Required parts would cost 
approximately $50 per airplane. Based on these figures, the cost impact 
of the proposed AD on U.S. operators is estimated to be $529,220, or 
$470 per airplane.
    The cost impact figure discussed above is 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 99-NM-47-AD.

    Applicability: Model 737-100, -200, -300, -400, and -500 series 
airplanes, line numbers 1 through 3016 inclusive, 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 (e) 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 a short circuit and overheating of the transient 
suppression diode, which could result in electrical arcing and 
ignition of fuel vapors at the fueling receptacle for the fuel 
tanks, and consequent fire during airplane fueling, accomplish the 
following:

Corrective Action

    (a) For Group 1 airplanes, as identified in Boeing Service 
Bulletin 737-28-1115, dated March 4, 1999: Within 12 months after 
the

[[Page 31764]]

effective date of this AD, install a transient suppression diode, 
part number (P/N) 69-58806-4, in the wire bundle (W264) of the 
refueling valve-to-float switch of each fuel tank, in accordance 
with the service bulletin.
    (b) For Groups 2, 3, and 4 airplanes, as identified in Boeing 
Service Bulletin 737-28-1115, dated March 4, 1999: Within 12 months 
after the effective date of this AD, replace the existing transient 
suppression diode, P/N 69-58806-1 or 69-58806-3, installed in the 
wire bundle (W264) of the refueling valve-to-float switch of each 
fuel tank, with an improved diode, P/N 69-58806-4, in accordance 
with the service bulletin.
    (c) Prior to further flight following accomplishment of the 
actions requied by paragraph (a) or (b) of this AD, perform a 
functional test to verify proper installation of each diode in 
accordance with Boeing Service Bulletin 737-28-1115, dated March 4, 
1999. If any discrepancy is detected during any functional test, 
prior to further flight, replace the discrepant diode and repeat the 
functional test, in accordance with the service bulletin.

Spares Paragraph

    (d) As of the effective date of this AD, no person shall install 
a transient suppression diode having P/N 69-58806-1 or 69-58806-3 on 
any airplane.

Alternative Methods of Compliance

    (e) 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 Aircraft Certification 
Office (ACO), FAA, Transport Airplane Directorate.
    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.

Special Flight Permits

    (f) Special flight permits may be issued in accordance with 
Secs. 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 June 7, 1999.
John J. Hickey,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-14934 Filed 6-11-99; 8:45 am]
BILLING CODE 4910-13-P