# 61 FR 48435: Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes > Federal · Regulations · In force URL: https://www.frixlaw.com/law-library/statutes/FR_PRORULE_96-23444 ## Section - **Citation:** 61 FR 48435 - **Heading:** Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes - **Jurisdiction:** Federal - **Kind:** Regulations - **Status:** In force - **Text as of:** August 14, 2026 - **Source:** Compiled text - **Location:** Federal Register / Vol. 61 / 61 FR 48435 ## Text 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: Kristin Larson, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-1760; fax (206) 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 96-NM-156-AD.'' The postcard will be date stamped and returned to the commenter. Availability of NPRMs th 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 96-NM-156-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-103, Attention: Rules Docket No. 96-NM-156-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Discussion The FAA has received reports of a discrepancy identified in the system that detects a loss of tension in the cable controlling the flaps (hereinafter called ``the detection system''), which is installed on certain Boeing Model 737-300, -400 and -500 series airplanes. Should an uncontained engine failure result in severing of the cable, this system detects the resultant loss of tension in the cable and turns off the hydraulic power that operates the flaps. Consequently, the flaps remain in the position in which they had been set prior to engine failure. A loss of tension in the cable causes a pulley arm mechanism in the detection system to move a magnet away from the proximity switch. This enables the switch to provide a ground to the relay that supplies electrical power for closing a bypass valve. When this valve is closed, hydraulic power to the flap power unit is turned off. An analysis of the detection system, performed by the manufacturer, showed that the pulley arm mechanism may not have sufficient clearance to move the magnet far enough from the proximity switch to activate the system. This condition, if not corrected, could cause movement of the flaps without action by the pilot, and ultimately could reduce the pilot's ability to control the airplane. Explanation of Relevant Service Information erformed by the manufacturer, showed that the pulley arm mechanism may not have sufficient clearance to move the magnet far enough from the proximity switch to activate the system. This condition, if not corrected, could cause movement of the flaps without action by the pilot, and ultimately could reduce the pilot's ability to control the airplane. Explanation of Relevant Service Information The FAA has reviewed and approved Boeing Alert Service Bulletin 737-27A1199, dated June 20, 1996, which describes procedures for removing a shim, if installed, from behind the proximity switch; and trimming the bracket for the proximity switch. These modifications will enable the pulley arm mechanism to move the magnet the distance necessary for activating the detection system. 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 removal of the shim behind the proximity switch, if installed; and trimming of the bracket for the proximity switch. The actions would be required to be accomplished in accordance with the service bulletin described previously. Cost Impact There are approximately 1,619 Model 737-300, -400, and -500 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 685 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 7 work hours per airplane to accomplish the proposed actions, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $287,700, or $420 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 Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $287,700, or $420 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] 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 96-NM-156-AD. Applicability: Model 737-300, -400 and -500 series airplanes having line production numbers 1001 through 2765, 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 otherwise 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 (b) 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 movement of the flaps from their last set position without action by the pilot, which could reduce controllability of the airplane, accomplish the following: e 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 movement of the flaps from their last set position without action by the pilot, which could reduce controllability of the airplane, accomplish the following: (a) Within 18 months or 3,200 hours time-in-service after the effective date of this AD, whichever occurs first, remove the shim, if installed, from behind the bracket of the proximity switch in the system which detects a loss of tension in the cable controlling the flaps; and trim this bracket; in accordance with Boeing Alert Service Bulletin 737-27A1199, dated June 20, 1996. (b) 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. (c) 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 September 6, 1996. James V. Devany, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. 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Check the current official text before relying on it. Not legal advice.