ASN Wikibase Occurrence # 42578
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| Date: | Wednesday 23 December 1998 |
| Time: | 13:51 LT |
| Type: |  Bell UH-1H |
| Owner/operator: | Westwind Helicopters, Inc. |
| Registration: | N4590 |
| MSN: | 65-09986 |
| Year of manufacture: | 1965 |
| Total airframe hrs: | 6774 hours |
| Engine model: | Lycoming T53-L-13B |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | Quincy, CA -
 United States of America
|
| Phase: | Unknown |
| Nature: | Unknown |
| Departure airport: | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
While conducting external load operations, the pilot radioed that the engine had failed. Witnesses reported visually observing the main rotor slowing and the individual blades becoming visible before the helicopter descended steeply into a reservoir from about 200 feet agl. The main rotor driveshaft, main rotor blades, and the tail rotor blades exhibited signatures consistent with low rotor rpm at impact. Engine examination revealed that the gas producer and power turbine assembly had failed as a result of the cumulative effects of thermal stress due to over-temperature operation. Further examination revealed that the exhaust gas temperature harness on the engine had a low signal output resulting in a low EGT indication in the cockpit which caused the company pilots to unknowingly operate the engine in excess of maximum EGT. According to other company pilots who flew this helicopter on typical external load operations, the engine would reach its EGT limit before the maximum torque was achieved. The operator did not routinely perform health indicator tests (HIT checks) which were developed by the U.S. Army to detect changes in engine power output. Review of the helicopter's FAA Type Certificate Data Sheet (H15NM) revealed the requirement for HIT checks to be accomplished prior to each takeoff and recorded in a log record.
Probable Cause: An inaccurate exhaust gas temperature gauge, that allowed the engine to be run over-temperature unknowingly by the pilot, which resulted in the subsequent failure of the turbine sections. Also causal was the pilot's failure to maintain rotor RPM during the autorotation. A factor in the accident was the operator's failure to adequately perform engine health indicator tests.
Accident investigation:
 |
|
Sources:
NTSB LAX99FA057
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 24-Oct-2008 10:30 | ASN archive | Added |
| 21-Dec-2016 19:24 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 22-Jul-2020 18:59 | harro | Updated [Narrative] |
| 04-Apr-2024 11:40 | ASN Update Bot | Updated [Time, Operator, Other fatalities, Phase, Nature, Source, Narrative, Category, Accident report] |
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