LAX99FA057 · Bell UH-1H
Bell UH-1H · Accident: total loss of engine power (mechanical failure) while maneuvering
Event
- NTSB case
- LAX99FA057
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 1 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Bell UH-1H
- Aircraft type
- Bell UH-1
- Category
- Helicopter
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N4590
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From not recordedTo not recorded
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 133: Rotorcraft Ext. Load
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Maneuvering · hover out of ground effect
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Total loss of engine power (mechanical failure)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Destroyed
Cause areas
- Engine instruments, egt/tot gage › Output low
- Pilot in command › Rotor RPM, not maintained
- Turboshaft engine, free(power) turbine › Disintegrated
- Turboshaft engine, free(power) turbine › Overtemperature
- Turboshaft engine, gas generator turbine › Disintegrated
- Turboshaft engine, gas generator turbine › Overtemperature
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
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.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record LAX99FA057
- Event ID
- 20001211X11576
- Case number
- LAX99FA057
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 1ff56fa8cc57faef14eb3000c5d8ab1d32c8ef751d6350af024ce93269872d09; retrieved 2026-09-20T22:17:22.542Z.