WPR17LA002 · Tamarack Helicopters Inc UH-1H
Farm Ag Enterprises Tamarack Helicopters Inc UH-1H · Accident: part(s) separation from aircraft while maneuvering
From Gila Bend, AZ to Gila Bend, AZ
Event
- NTSB case
- WPR17LA002
- 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
Tamarack Helicopters Inc UH-1H
- Aircraft type
- Tamarack 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
- N175SF
- Operator
- Farm Ag Enterprises
- Onboard fatalities
- Unknown
- Route
- From Gila Bend, AZTo Gila Bend, AZ
- Aircraft age
- About 47 years (built 1969)
- 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 137: Agricultural
- 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 · low-altitude flying
- 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
- Part(s) separation from aircraft
- 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
While the helicopter was maneuvering at low altitude after an agricultural application, its 90° tail rotor gearbox separated. The commercial pilot performed an autorotation, and the helicopter rolled over on impact.
The gearbox had been installed about 300 flight hours before the accident. Postaccident examination revealed that the gearbox separation was the result of fatigue fracturing of its six attaching studs, which, once failed, liberated the gearbox from the input quill sleeve. Fatigue is typically the result of insufficient preload in the fastener often due to insufficient torque during installation or by the loss of preload after installation. Fretting wear on the studs and in the holes indicated that there were small amounts of relative movement between these components and thereby also indicated insufficient preload. However, the interface between the input quill housing and the vertical fin showed no significant fretting or wear.
The locations of the main fatigue origins in the studs and the fretting location between the studs and fin holes were both consistent with normal torsional loads in the tail rotor drive system. The studs exhibited a large percentage of fatigue penetration before final stud separation and relatively small overstress zones. These signatures are indicative of a low mean stress and a large number of small tail rotor inputs (loads) consistent with repetitive aerial application flight profiles.
The helicopter, which was originally designed and manufactured for the military, was never made commercially available. As such, individual owners and companies were responsible for certification and continued airworthiness of this and other surplus military aircraft.
A review of National Transportation Safety Board records indicated two accidents involving similar failures on this helicopter type. Both were surplus military helicopters flying in the restricted category and used in highly repetitive cycle work that would require significant tail rotor inputs.
Probable cause
The separation of the 90° tail rotor gearbox assembly as a result of fatigue to the tail rotor gearbox input quill assembly attachment studs due to the helicopter experiencing highly repetitive agricultural flight profiles for which it was not designed.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR17LA002
- Event ID
- 20161005X45137
- Case number
- WPR17LA002
- 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: 71a3281e5d0c681577b9513f6726499c2b51874f73f4214fc0134285d9f99166; retrieved 2026-09-16T04:21:24.718Z.