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

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 737-300, -400, and -500 series airplanes.

This proposal would require repetitive inspections of certain connectors located in the main wheel wells to detect discrepancies; and corrective action, if necessary. This action is necessary to detect and correct such discrepancies, which could result in electrical arcing of the connectors, uncommanded closure of the engine fuel shut-off valves, and consequent in-flight loss of thrust or engine shutdown from lack of fuel. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by October 12, 2000.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-39-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. Comments may be submitted via fax to (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 2000-NM-39-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text.

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:

Stephen Oshiro, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2793; 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.

Submit comments using the following format:

• Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
• For each issue, state what specific change to the proposed AD is being requested.
• Include justification (e.g., reasons or data) for each request.

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 2000-NM-39-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. 2000-NM-39-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received reports indicating engine shutdown during flight due to uncommanded movement of the engine shutoff valve on three Model 737 series airplanes. Investigation revealed that connectors located in certain disconnect panels had burned and were damaged, and the printed circuit cards located in the fuel system module were also damaged. Examination of connectors and cards returned to the manufacturer indicated that a short occurred between the contacts for the outboard landing lights and the contacts for the fuel shut-off valve mounted on the wing rear spar. In one incident the spare contacts and filler rods normally installed in the unused cavities of the connectors were not installed, creating a path for contamination to enter the connectors through the open, unused cavities. However, the absence of spare contacts and filler rods cannot be verified as the single cause of the contamination. Therefore, the FAA has determined that the contamination also could occur when the connectors are properly fitted with spare contacts and filler rods. Such conditions, if not detected and corrected, could result in electrical arcing of the connectors, uncommanded closure of the engine fuel shut-off valves, and consequent in-flight loss of thrust or engine shutdown from lack of fuel.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Service Letter 737-SL-24-138, dated May 24, 1999, which describes procedures for inspections of certain connectors (connectors are linked to the fuel shut-off valves and outboard landing lights) located in the main wheel wells, to detect discrepancies including missing spare contacts and filler rods, improper plugs or filler rods, or contamination or corrosion of the connectors. If any discrepancies are found, the service letter references Boeing Standard Wiring Practices Manual D6-54446, Subject 20-60-01, for cleaning corroded or contaminated wiring; Subject 20-61-11, for installing spare contacts in the connectors; and Subject 20-60-08, for installing filler rods in the connectors.

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 letter described previously, except as discussed below.

Differences Between Service Letter and This Proposed AD

Operators should note that, although the service letter does not specify the type of inspection of the connectors to detect contamination or missing spare contacts and filler rods, this proposed AD would require a detailed visual inspection for accomplishment of the actions. A note has been included in this proposed rule to define that inspection.

Operators also should note that this proposed AD would require the detailed visual inspection be accomplished within 12 months after the effective date of the AD, and repeated at 18-month intervals thereafter. The service letter identifies a one-time inspection at “the next convenient maintenance opportunity.” In developing an appropriate compliance time for this proposed AD, the FAA considered 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 inspection (approximately 1 hour). In light of all of these factors, the FAA finds a 12-month compliance time for the initial inspection, and an 18-month repetitive inspection interval, to be warranted, in that those times represent appropriate intervals for affected airplanes to continue to operate without compromising safety.

While Boeing Service Letter 737-SL-24-138 limits its effectivity to Model 737-300, -400, and -500 series airplanes having line numbers prior to 3095, this proposed AD would be applicable to all Model 737-300, -400, and -500 series airplanes. In light of the fact that the exact cause of the contamination entering the connectors for the engine fuel shut-off valves mounted on the wing rear spar and for the outboard landing lights is as yet undetermined, and may be caused by spare contacts and filler rods that fall out or leak during service or by connectors that are properly fitted with spare contacts and filler rods, the FAA has determined that all airplanes, as stated above, must accomplish the requirements of this proposed AD.

Cost Impact

There are approximately 1,974 Model 737 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 755 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 1 work hour per airplane to accomplish the proposed inspection, and that the average labor rate is $60 per work hour. The cost of required parts would be negligible. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $45,300, or $60 per airplane, per inspection cycle.

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 proposed AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions.

Regulatory Impact

The regulations proposed herein would 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. Therefore, it is determined that this proposal would not have federalism implications under Executive Order 13132.

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.