# AD 72-21-06: Crankcase Bearings

- Type: Airworthiness directive
- Status: Current
- Products: Lycoming Engines IGSO-540-A1A, IGSO-540-A1C, IGSO-540-A1D, IGSO-540-A1E, IGSO-540-A1F, IGSO-540-B1A and IGSO-540-B1C
- Effective: October 17, 1972
- Superseded by: Nothing supersedes this AD
- Product type: Engine
- Amendment: 39-1535
- Registered aircraft: 48 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/A9D01E1D9F0F13228625682A00547252.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/72-21-06

## The airworthiness directive

72-21-06 AVCO LYCOMING: Amendment 39-1535. Applies to IGSO-540-A series engines except S/N 2537-50 and subsequent; and IGSO-540-B series engines except S/N 2541-50 and subsequent; and IGSO-540-A and -B engines S/N 747-50, 844-50, 852-50, 947-50, 1184-50, 1240-50, 1361-50, 1402-50, 1453-50, 1544-50, 1767-50, 1773-50, 1794-50, 1799-50, 1933-50 overhauled (also known as remanufactured) by Lycoming after 26 January 1970. To prevent shifting and possible failures of the crankcase bearings perform the following: (a) Engines that have accumulated less than 500 hours in service since new or overhaul must have the lubrication system inspected for metal contaminants within the next 10 hours in service after the effective date of this AD and every 25 hours in service thereafter. Further, at the accumulation of 525 hours in service compliance with (d) or (f) is required. (b) Engines that have accumulated 500 hours or more in service since new or overhaul must have the lubrication system inspected for metal contaminants within the next 10 hours in service after the effective date of this AD, and every 25 hours in service thereafter. Further, compliance with (d) or (f) is required within 25 hours in service after the effective date of this AD. (c) Compliance with (d) or (f) is required if metal contaminants are detected during the above inspections. (d) Remove number four cylinder and examine visually the position of number three main bearing for shifting in accordance with Part II of Avco Lycoming Service Bulletin No. 327B. Should shifting be detected, comply with paragraph (f). (e) Unless already accomplished, compliance with paragraph (f) is required within 50 hours in service after the effective date of this AD on engines that have accumulated 1200 hours or more in service since new or last overhaul. (f) Repair the crankcase as described in Lycoming Service Instructions No. 1112C and install straight crankcase bearing dowels per Lycoming Service Bulletin No. 326 or equivalent repair and alteration approved by Chief, Engineering and Manufacturing Branch, FAA, Eastern Region. Compliance with the provisions of this paragraph eliminates the inspection requirements of this AD. This amendment is effective October 17, 1972.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS 1E7](https://openairdocs.org/tcds/1E7): Lycoming Engines; names 7 of 8 models: IGSO-540-A1F, IGSO-540-B1A, IGSO-540-A1C, IGSO-540-A1A, IGSO-540-B1C, IGSO-540-A1D, IGSO-540-A1E

## 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: 48 (0 by airframe model, 48 by engine model)
- Makers: Beech 18, Aero Commander 17, Piper 7, Cessna 2, Mooney 2, Dornier 1, Hiller 1

Models with the most aircraft:

- [Lycoming IGSO-540-B1A](https://openairdocs.org/engine/lycoming-igso-540-b1a): 48 aircraft (engine model)

All 1 models: https://openairdocs.org/ad/72-21-06/models.md
Every aircraft: https://openairdocs.org/ad/72-21-06/aircraft.md

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.