# AD 91-09-14 R1: Engine Mount - Type: Airworthiness directive - Status: Historical - Products: Boeing 737-100 Series, 737-200 Series and 737-200C Series - Effective: May 18, 1994 - Superseded by: [AD 99-26-07](https://openairdocs.org/ad/99-26-07) - Product type: Aircraft, Large airplane - Amendment: 39-8876 - Docket: 93-NM-170-AD - Registered aircraft: 10 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/AD5BE91A2FECCF8586256A18006C2B49.0001 - DRS record last changed: August 7, 2025 - Page: https://openairdocs.org/ad/91-09-14-R1 ## The airworthiness directive 91-09-14 R1 BOEING: Amendment 39-8876. Docket 93-NM-170-AD. Revises AD 91-09-14, Amendment 39-6972. Applicability: All Model 737-100, -200, and -200C series airplanes, certificated in any category. Compliance: Required as indicated, unless accomplished previously. To prevent failure of the secondary support to sustain engine loads, in the event of failure of the aft engine mount cone bolt, which could result in engine separation from the wing, accomplish the following: (a) Within the next 45 landings after May 20, 1991 (the effective date of AD 91-09-14, amendment 39-6972), accomplish the following: (1) Inspect the aft mount cone bolt indicator for proper alignment. Improper alignment indicates a broken aft cone bolt. Broken cone bolts must be replaced, prior to further flight, with bolts that have been inspected in accordance with Boeing Alert Service Bulletin 737-71A1212, dated December 22, 1987, using magnetic particle inspection techniques. Repeat the inspection of the indicator at intervals thereafter not to exceed 45 landings. (2) Unless previously accomplished within the last 255 landings, inspect the aft mount cone bolt improved secondary support for missing nuts, evidence of bolt wear, and disbonded honeycomb core in accordance with Boeing Service Bulletin 737-71-1250, dated June 14, 1990. Except as provided in paragraph (b) of this AD, missing nuts, bolts worn outside the limits specified in the service bulletin, or disbonded honeycomb core must be replaced, prior to further flight, with new or repaired identical parts. Repeat the inspection at intervals not to exceed 300 landings. (b) Perform the following inspections if discrepant hardware is found during the inspections required by paragraph (a)(2) of this AD, and replacement hardware is not immediately available: (1) Prior to further flight, and thereafter at intervals not to exceed 300 landings, inspect for cracks in the aft engine mount cone bolt, in accordance with Boeing Alert Service Bulletin 737-71A1212, dated December 22, 1987, using ultrasonic inspection techniques. Replace cracked cone bolts, prior to further flight, with bolts that have been inspected in accordance with the above service bulletin, using magnetic particle inspection techniques. Replacement (newly installed) cone bolts must be ultrasonically inspected for internal cracking in accordance with the provisions of this paragraph at intervals not to exceed 300 landings. (2) At the next ultrasonic inspection, as required by paragraph (b)(1) of this AD, unless previously accomplished within 150 to 300 landings after cone bolt installation, accomplish a torque check to verify that the cone bolt is torqued to the proper torque limit specified in the appropriate Boeing maintenance manual. This check is to be accomplished without loosening the bolt. After every cone bolt installation, accomplish the torque check procedure required by this paragraph, between150 landings and 300 landings following installation. Replacement of discrepant hardware in accordance with paragraph (a)(2) of this AD constitutes terminating action for the requirements of this paragraph. (i) If the cone bolt torque is below one-half the specified torque, remove the cone bolt and replace it with a serviceable bolt. (ii) If the cone bolt torque is equal to, or above one-half the specified torque, but below the specified torque, re-torque to the specified level and re-check the torque within the next 150 to 300 landings. If, at that time, the torque is below 90 percent of the specified torque, replace the cone bolt with a serviceable bolt. (c) Replacement of the existing aft engine mount secondary support with a new, modified secondary support, Kit Number 65C37057-1, in accordance with Boeing Service Bulletin 737-71-1289, dated August 19, 1993, constitutes terminating action for the inspections required by paragraphs (a)(2), (b), (b)(1), and (b)(2) of this AD. (d) 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: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. (e) Special flight permits may be issued in accordance with Federal Aviation Regulations (FAR) 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished. (f) The optional replacement shall be done in accordance with Boeing Service Bulletin 737-71-1289, dated August 19, 1993. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. (g) This amendment becomes effective on May 18, 1994. ## Affected data sheets (1) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS A16WE](https://openairdocs.org/tcds/A16WE): The Boeing Company; names 3 of 17 models: 737-100 Series, 737-200C Series, 737-200 Series ## Registered aircraft it may apply to (OpenAirDocs) Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment. - Aircraft: 10 (10 by airframe model, 0 by engine model) - Makers: Boeing 10 Models with the most aircraft: - [Boeing 737-205](https://openairdocs.org/model/boeing-737-205): 3 aircraft (airframe model) - [Boeing 737-200](https://openairdocs.org/model/boeing-737-200): 1 aircraft (airframe model) - [Boeing 737-201](https://openairdocs.org/model/boeing-737-201): 1 aircraft (airframe model) - [Boeing 737-210C](https://openairdocs.org/model/boeing-737-210c): 1 aircraft (airframe model) - [Boeing 737-242C](https://openairdocs.org/model/boeing-737-242c): 1 aircraft (airframe model) - [Boeing 737-290C](https://openairdocs.org/model/boeing-737-290c): 1 aircraft (airframe model) - [Boeing 737-209](https://openairdocs.org/model/boeing-737-209): 1 aircraft (airframe model) - [Boeing 737-275C](https://openairdocs.org/model/boeing-737-275c): 1 aircraft (airframe model) All 8 models: https://openairdocs.org/ad/91-09-14-R1/models.md Every aircraft: https://openairdocs.org/ad/91-09-14-R1/aircraft.md ## Related documents - [AD 99-26-07](https://openairdocs.org/ad/99-26-07): Aft Engine Mount Cone Bolt ยท Boeing 737-100 Series, 737-200 Series and 737-200C Series. Effective Jan 24, 2000. Supersedes this AD Its text cites no advisory circulars or STCs. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.