WPR12LA039 · Williams Helicopter Corp UH-1H
Airwest Helicopters Williams Helicopter Corp UH-1H · Accident: system/component malfunction/failure (non-power) en route
From Valle Airport (40G) to Supai, AZ
Event
- NTSB case
- WPR12LA039
- 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
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- 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
Williams Helicopter Corp UH-1H
- Aircraft type
- Williams 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
- N502AW
- Operator
- Airwest Helicopters
- Onboard fatalities
- Unknown
- Route
- From Valle Airport (40G), Grand Canyon, AZTo Supai, AZ
- 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 91: General Aviation
- 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
- En route · cruise
- Defining eventThe 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
- System/component malfunction/failure (non-power)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Aircraft › Aircraft propeller/rotor
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
According to the pilot, the helicopter was about 500 ft above ground level (agl) when he saw the master caution warning light illuminate; he then saw that the low transmission oil pressure light was also illuminated. He immediately maneuvered away from power lines and set up an approach to land. While descending, the helicopter yawed left and right, and, about 10 ft agl with the airspeed almost at 0, the main rotor speed slowed and then stopped, and the helicopter subsequently fell to the ground. The pilot reported that the engine continued to operate for about 15 seconds after impact.
An on-scene examination revealed that both main rotor blades remained intact with no leading edge damage. Examination of the helicopter revealed a band of discoloration around the circumference of the transmission case near the main rotor reduction gear assembly; localized paint peeling was also noted. There were no oil stains or residue on the transmission case.
During the subsequent transmission disassembly, the mast was found coated in metal debris along its length, and the mast bearing was found coated in oil. Molten metal pieces were found in the upper planetary gears, ring gear, and sun gear, consistent with insufficient lubrication. The lower planetary gears sustained significant damage from the molten metal pieces. There was no damage to the transmission oil pump, oil was present in the oil pump cavity, and some debris and scoring were evident on the housing.
Examination of the passages within the transmission oil manifold revealed medium-to-high density particles in several of the passages, but none of the passages were blocked; particles were also found in the chip detector. The particles were identified as being generally composed of metals commonly used in gears, housings, and bushings. The damage to the transmission indicated that it likely seized as a result of an overtemperature condition due to a lack of lubrication. Due to the severity of the damage, the reason for the lack of lubrication could not be determined.
Probable cause
The loss of main rotor power due to a main rotor transmission failure from a lack of lubrication.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR12LA039
- Event ID
- 20111116X32140
- Case number
- WPR12LA039
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
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: 8503e82ab6d38de44dfaf73c338c9859a856c1ca92cb956bc92135105ff67bcd; retrieved 2026-09-15T16:56:25.112Z.