ASN Wikibase Occurrence # 354575
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| Date: | Monday 20 April 1998 |
| Time: | 21:30 LT |
| Type: |  Bell 206L-1 |
| Owner/operator: | Helinet |
| Registration: | N87WC |
| MSN: | 45201 |
| Total airframe hrs: | 3738 hours |
| Engine model: | Allison 250-C28B |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Los Angeles, CA -
 United States of America
|
| Phase: | Approach |
| Nature: | Unknown |
| Departure airport: | Ontario, CA (KONT) |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The helicopter lost engine power while on approach to a rooftop helipad, approximately 50 feet high and 50 feet short of the building. The pilot landed the helicopter on the roof, severing the tail boom at the horizontal stabilizer. The Safety Board conducted a teardown examination of the engine. Disassembly of the gas producer turbine support from the power turbine support revealed a fractured first stage turbine wheel, which displayed a nine airfoil chordal segment of the rim separated from the larger portion of the wheel. According to the Allison metallurgist, both the first and second stage turbine wheel blades exhibited evidence of operation of temperatures in excess of 2,200 degrees Fahrenheit. Both primary and secondary rim crack fractures exhibited evidence of exposure to extreme temperatures during the engine start sequence. No evidence of engine oil fire was observed on the gas producer turbine components. Chemical analysis of the affected gas producer turbine components indicated conformance to the specified material types. The Allison metallurgist reported that an overtemperature event occurred as a result of a hot start when both wheels were not at operating temperature; an overtemperature event occurring when the engine was at operating temperatures would have melted the first stage turbine wheel blades. The size of the gamma prime at the altered locations indicated the event occurred approximately within the last 10 hours of engine operation. No hot start or overtemperature event was reported to the maintenance facility.
Probable Cause: An overtemp of the engine during start within 10 hours of the accident, and the failure to report the event to the maintenance facility.
Accident investigation:
 |
|
Sources:
NTSB LAX98LA140
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 11-Mar-2024 16:00 | ASN Update Bot | Added |
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