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 replacement of the existing autothrottle computer with a new, improved autothrottle computer. This proposal is prompted by reports of asymmetric thrust conditions during flight caused by irregular autothrottle operation in which the thrust levers slowly move apart causing the airplane to bank excessively and go into a roll. The actions specified by the proposed AD are intended to prevent such conditions, which could result in loss of control of the airplane.

DATES:

Comments must be received by July 27, 2000.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-107-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:

Thanh Truong, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2552; 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 2000-NM-107-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-107-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received reports on certain Boeing Model 737-300, -400, and -500 series airplanes indicating an asymmetric thrust condition caused by irregular autothrottle operation, in which the thrust levers slowly move apart causing the airplane to bank and roll. This thrust condition exceeds the autopilot roll authority and results in a bank angle of more than 30 degrees. In one incident, the airplane rolled more than 46 degrees without crew recognition. Without pilot intervention, an airplane that has asymmetric thrust can bank excessively and go into a roll. Such conditions, if not corrected, could result in loss of control of the airplane.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletin 737-22A1130, dated September 24, 1998, which describes procedures for replacement of the existing autothrottle computer with a new, improved autothrottle computer. The improved autothrottle computer disengages the autothrottle if an asymmetric thrust condition is detected, and prevents the airplane from rolling to an excessive bank angle.

Accomplishment of the actions specified in the alert service bulletin is intended to adequately address the 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 alert service bulletin described previously, except as discussed below.

Differences Between Proposed Rule and Alert Service Bulletin

Operators should note that this proposed AD would require replacement of the autothrottle computer to be accomplished within one year after the effective date of this AD. The alert service bulletin recommends that this replacement should be accomplished “as soon as manpower and materials are available.” However, in developing an appropriate compliance time for the proposed replacement, the FAA considered not only the degree of urgency associated with addressing the subject unsafe condition, but also the number of proposed requirements and the availability of required parts. The FAA has determined that one year represents an appropriate interval of time allowable wherein all of these actions can be accomplished during scheduled airplane maintenance and an ample number of required parts will be available for modification of the U.S. fleet within the proposed compliance period. The FAA also finds that such a compliance time will not adversely affect the safety of the affected airplanes.

Cost Impact

There are approximately 1,974 airplanes of the affected design in the worldwide fleet. The FAA estimates that 799 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 replacement, and that the average labor rate is $60 per work hour. Required parts would cost between $1,400 and $4,200 per airplane. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be between $1,460 and $4,260 per airplane.

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 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.