ASN Wikibase Occurrence # 295644
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| Date: | Wednesday 25 June 2003 |
| Time: | 08:00 LT |
| Type: |  Mcdonnell Douglas 369E |
| Owner/operator: | U.S. Department of Agriculture APHIS |
| Registration: | N1502 |
| MSN: | 0324E |
| Year of manufacture: | 1989 |
| Total airframe hrs: | 7866 hours |
| Engine model: | Allison 250-C20B |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Big Timber, MT -
 United States of America
|
| Phase: | Unknown |
| Nature: | Unknown |
| Departure airport: | Big Timber, MT (6S0) |
| Helena Airport, MT (HLN/KHLN) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
While operating at an altitude of about 40 feet and 40 knots airspeed on a low level coyote predation flight the pilot of the (Hughes) McDonnell Douglas 369E helicopter heard a loud bang and observed both the "Engine Out" and "Auto Relight" warning lights illuminate. The pilot reduced collective and immediately transitioned to a forced landing onto uneven terrain during which the helicopter touched down hard and the right skid separated. Post-crash examination of the Rolls Royce (Allison) 250-C20B turboshaft engine revealed that the compressor coupling adapter had fractured circumferentially resulting in the disconnection of the compressor from the turbine assembly. Further examination revealed that the Rolls Royce (Allison) manufactured compressor adapter coupling had been installed approximately 1,005 hours earlier and that the separation had been the result of multiple fatigue fractures in the coupling associated with severe fretting on the adapter's outer diameter where it inserts into the spur adapter gearshaft.
Probable Cause: Fretting on the outside diameter of the compressor coupling adapter which resulted in fatigue and subsequent fracture of the adapter, and ultimately the disconnection of the compressor from the turbine assembly. Contributing factors were low rotor RPM, uneven terrain and collapse of the right skid on landing.
Accident investigation:
 |
|
Sources:
NTSB SEA03TA116
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 13-Oct-2022 11:00 | ASN Update Bot | Added |
| 12-Nov-2022 02:11 | Ron Averes | Updated [Operator, Location, Narrative] |
Corrections or additions? ... Edit this accident description
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