# AD 91-14-22: Crankshaft Gear Retaining Bolt - Type: Airworthiness directive - Status: Historical - Products: Textron Lycoming, AVCO --All engine models - Effective: August 19, 1991 - Superseded by: [AD 2004-10-14](https://openairdocs.org/ad/2004-10-14) - Product type: Engine - Amendment: 39-6916 - Docket: 89-ANE-10 - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/58250015E75110778625684F006DAFC8.0001 - DRS record last changed: August 7, 2025 - Page: https://openairdocs.org/ad/91-14-22 ## The airworthiness directive 91-14-22 TEXTRON LYCOMING: Amendment 39-6916. Docket No. 89-ANE-10. Applicability: Textron Lycoming (formerly Avco Lycoming) direct drive piston aircraft engines (except: O-320-H, O-360-E, LO-360-E, TO-360-E, LTO-360-E and TIO-541 series engines). Compliance: Required at each engine overhaul, after a propeller strike, sudden stoppage, or whenever gear train repair is required. A propeller strike for the purpose of this AD, is defined as a sudden engine stoppage, or loss of a propeller blade or tip. NOTE: Avco Lycoming Service Letter No. L163B dated December 23, 1977, "Recommendations Regarding Accidental Engine Stoppage, Loss of Propeller Blade or Tip," contains additional information on the subject. To prevent loosening or failure of the crankshaft gear retaining bolt, which may cause sudden engine failure, accomplish the following: (a) Inspect the crankshaft counterbored recess, the alignment dowel, the retaining bolt and lock plate, the bolt hole threads, and the crankshaft gear for wear, galling, corrosion, and fretting in accordance with Sections 1 through 7, including all tables and figures in Textron Lycoming Service Bulletin (SB) No. 475, Revision A, dated July 16, 1990. (b) Prior to further flight, repair, rework, or replace damaged or worn parts as identified in paragraph (a) of this AD. (1) Repair and rework crankshaft pilot diameter in accordance with Textron Lycoming SB 475, Revision A, dated July 16, 1990, and replace dowel pin with appropriate size dowel as shown in Table 1 of the service bulletin. (2) Insure that the tapped threads in the gear retaining bolt hole of the crankshaft are clean and undamaged. If threads are damaged, replace crankshaft with a serviceable unit, or have threads repaired by an FAA approved facility specifically approved to do that repair. (3) Inspect the counterbored gear mounting face of the crankshaft to ensure there is no damage due to fretting or galling, as damageof this nature is unrepairable. (4) Repair crankshaft counterbore pilot diameter, if necessary, in accordance with Section 3 of Textron Lycoming SB No. 475, Revision A, dated July 16, 1990. (5) Verify that the crankshaft gear incorporates three .75 inch radius scallops on the flange as shown in Figure 5 of Textron Lycoming SB No. 475, Revision A, dated July 16, 1990. Assemble gear onto crankshaft using a new retaining bolt and lockplate and insure fit of mating parts as described in Section 6 and Figure 6 of the Textron Lycoming Service Bulletin No. 475, Revision A, dated July 16, 1990. (c) Aircraft maybe ferried in accordance with the provisions of FAR 21.197 and 21.199 to a base where the AD can be accomplished. (d) Upon submission of substantiating data by an owner or operator through an FAA Inspector (maintenance, avionics, or operations, as appropriate), an alternate method of compliance with the requirements of this AD or adjustments to the compliance schedule specified in this AD may be approved by the Manager, New York Aircraft Certification Office, Engine and Propeller Directorate, Aircraft Certification Service, FAA, 181 South Franklin Avenue, Room 202, Valley Stream, New York 11581. The inspection procedures shall be done in accordance with the following Textron Lycoming document: DOCUMENT NO. PAGE NO. ISSUE/REV. DATE SB 475 1-4 A 07/16/90 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 Textron Lycoming, Oliver Street, Williamsport, Pennsylvania 17701. Copies may be inspected at the FAA, New England Region, Office of the Assistant Chief Counsel, 12 New England Executive Park, Burlington, Massachusetts 01803, or at the Office of the Federal Register, 1100 L Street, NW, Room 8401, Washington, DC. This amendment (39-6916, AD 91-14-22) becomes effective on August 19, 1991. ## Registered aircraft it may apply to (OpenAirDocs) No registered aircraft matched the models it names. ## Related documents - [AD 2004-10-14](https://openairdocs.org/ad/2004-10-14): Crankshaft gear · Lycoming Engines AEIO-320-D1B, AEIO-320-D2B, AEIO-320-E1A and 642 more. Effective Jun 25, 2004. Supersedes this AD Its text cites no advisory circulars or STCs. ## NTSB investigations that cite this AD (6) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB LAX01LA179](https://openairdocs.org/ntsb/LAX01LA179), May 17, 2001: Piper PA-32RT-300T (N22467), Paulden, AZ, substantial damage. Probable cause: Catastropic engine failure due to oil depletetion caused by an oil filter gasket failure. - [NTSB LAX99LA029](https://openairdocs.org/ntsb/LAX99LA029), Nov 12, 1998: Piper PA-28-150 (N991PK), Gila Bend, AZ, substantial damage. Probable cause: The crankshaft gear attach bolt loosening and backing out of its crankshaft bore, which led to the fatigue failure of the crankshaft gear dowel pin due to excessive working of the gear. The sequence… - [NTSB FTW99LA017](https://openairdocs.org/ntsb/FTW99LA017), Oct 29, 1998: Grumman American AA-5A (N9956U), Scott, AR, substantial damage. Probable cause: The disengagement of the crankshaft gear due to the maintenance personnel not installing the gear lockplate at the last engine overhaul, resulting in the loosening of the gear retaining bolt, and the… - [NTSB LAX97FA047](https://openairdocs.org/ntsb/LAX97FA047), Nov 21, 1996: Piper PA-28-236 (N8447B), Lost Hills, CA, destroyed, 1 fatal. Probable cause: The pilot's continued VFR flight into instrument meteorological conditions, which led to spatial disorientation and loss of aircraft control, and the pilot exceeding the aircraft's design stress… - [NTSB FTW95LA117](https://openairdocs.org/ntsb/FTW95LA117), Feb 17, 1995: Cessna 172RG (N5096U), Plano, TX, substantial damage. Probable cause: THE DISENGAGEMENT OF THE CRANKSHAFT GEAR DUE TO THE LOOSENING OF THE GEAR RETAINING BOLT AND THE SUBSEQUENT FRACTURE OF THE GEAR ALIGNMENT DOWEL. A FACTOR WAS THE LACK OF SUITABLE TERRAIN AVAILABLE… - [NTSB FTW94FA300](https://openairdocs.org/ntsb/FTW94FA300), Sep 18, 1994: Piper PA-24-260 (N9159P), Tennesse Colony, TX, substantial damage, 2 fatal. Probable cause: THE PILOT'S FAILURE TO MAINTAIN AIRSPEED AND THE RESULTANT INADVERTENT STALL/SPIN. A FACTOR WAS THE LOSS OF ENGINE POWER FOR UNDETERMINED REASONS. --- 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.