# AD 76-17-08 R1: Main Rotor Shaft - Type: Airworthiness directive - Status: Historical - Products: Enstrom Helicopter Corporation, The 280, F-28 and F-28A - Effective: October 4, 1977 - Superseded by: [AD 2001-22-01](https://openairdocs.org/ad/2001-22-01) - Product type: Aircraft, Rotorcraft - Amendment: 39-3043 - Registered aircraft: 45 may be affected, by airframe or engine model (OpenAirDocs) - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/21EB70C9139B645486256A38004DA186.0001 - DRS record last changed: August 7, 2025 - Page: https://openairdocs.org/ad/76-17-08-R1 ## The airworthiness directive 76-17-08 ENSTROM: Amendment 39-2700 as amended by Amendment 39-3043. Applies to Models F-28, F-28A, and 280 helicopters certificated in all categories, except for those helicopters which have the following main rotor shaft gear box serial numbers. 032FS 07-012-74PS 39-002-13PS 041PS 08-001-72S 44-011-76PS 067PS 10-002-72PS 44-019-76PS 070PS 19-024-74PS 53-003-73PS 091 34-029-75PS To detect tool marks, surface irregularities, and cracks which may develop into failure of the Main Rotor Shaft (Enstrom Part Number 28-13104) accomplish the following: A. Before further flight visually inspect the main rotor shaft in the area of the radius beneath the rotor hub shoulder, using an eight power or greater magnifying glass and report to the Enstrom Helicopter Corporation, Menominee County Airport, P.O. Box 277, Menominee, Michigan, Phone 906-863-9971, any evidence of circumferentially disposed tool marks or surface irregularities. B. Before further flight, unless previously accomplished within the last 20 hours time in service or one month, and every 20 hours or one month thereafter, whichever occurs first, inspect the main rotor shaft for cracks in the area of the radius beneath the rotor hub shoulder using a 3-step dye-penetrant method. The inspections are to be performed by maintenance personnel familiar with the dye-penetrant inspection method. C. Within 10 hours time in service or 15 days, whichever occurs first after each dye- penetrant inspection, visually check the main rotor shaft for cracks in the area of the radius beneath the rotor hub shoulder using an eight power or greater magnifying glass. D. Before further flight remove from service any main rotor shaft found to contain cracks or other evidence of damage and replace with an airworthy shaft of the same part number or later FAA approved part number. E. Immediately check in accordance with Paragraph B above any helicopter which develops unusual once-per-rotor-revolution vibration. Such vibrations serve as warning of imminent failure. F. Within the next 200 hours time in service or six months after the effective date of this amendment, whichever occurs first, remove main rotor shaft from service or return gearbox and shaft to Enstrom Helicopter Corporation for modification in accordance with Enstrom Service Directed Bulletin No. 0036. G. Repetitive inspections of paragraphs B and C above may be discontinued after main rotor shaft modification in accordance with Enstrom Service Directed Bulletin No. 0036. The manufacturer's specifications and procedures identified and described in this directive are incorporated herein and made a part hereof pursuant to 5 U.S.C. 552(a)(1). All persons affected by this directive who have not already received these documents from the manufacturer may obtain copies upon request to the Enstrom Helicopter Corporation, Menominee County Airport, P.O. Box 277, Menominee, Michigan 49858. These documents may also be examined at the FAA Great Lakes Region, Engineering and Manufacturing Branch, AGL-210, 2300 East Devon Avenue, Des Plaines, Illinois. A historical file on this AD which includes the incorporated material in full is also maintained at that office. Amendment 39-2700 superseded Amendment 39-2472 (40 F.R. 59197), AD 75-26-19. Amendment 39-2700 became effective September 1, 1976 and was effective immediately for all recipients of the airmail letters dated August 6, 1976 which contained this amendment. This amendment 39-3043 becomes effective October 4, 1977. ## Affected data sheets (1) (OpenAirDocs) The type certificate data sheets whose models the AD names. - [TCDS H1CE](https://openairdocs.org/tcds/H1CE): The Enstrom Helicopter Corporation; names 3 of 14 models: 280, F-28, F-28A ## 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: 45 (45 by airframe model, 0 by engine model) - Makers: Enstrom 44, Enstrom Helicopter 1 Models with the most aircraft: - [Enstrom F-28A](https://openairdocs.org/model/enstrom-f-28a): 38 aircraft (airframe model) - [Enstrom 280](https://openairdocs.org/model/enstrom-280): 5 aircraft (airframe model) - [Enstrom Helicopter F-28A](https://openairdocs.org/model/enstrom-helicopter-f-28a): 1 aircraft (airframe model) - [Enstrom F-28](https://openairdocs.org/model/enstrom-f-28): 1 aircraft (airframe model) All 4 models: https://openairdocs.org/ad/76-17-08-R1/models.md Every aircraft: https://openairdocs.org/ad/76-17-08-R1/aircraft.md ## Related documents - [AD 2001-22-01](https://openairdocs.org/ad/2001-22-01) (historical): Main Rotor Shaft ยท Enstrom Helicopter Corporation, The 280, 280C, 280F and 8 more. Effective Nov 13, 2001. Supersedes this AD Its text cites no advisory circulars or STCs. ## NTSB investigations that cite this AD (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB IAD01LA031](https://openairdocs.org/ntsb/IAD01LA031), Feb 3, 2001: Enstrom F28A (N98PM), Napoleon, OH, substantial damage. Probable cause: The fatigue failure in the fillet radius of the mast, which resulted in the separation of the main rotor system. --- 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.