ERA21LA386 · Hiller UH-12E
Hiller UH-12E · Accident: system/component malfunction/failure (non-power) en route
From Metter, GA to an unrecorded destination
Event
- NTSB case
- ERA21LA386
- 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
- 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
Hiller UH-12E
- Aircraft type
- Hiller UH-12
- 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
- N430NR
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Metter, GATo not recorded
- Aircraft age
- About 60 years (built 1961)
- 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
- 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
- Personnel issues › Task performance
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
During cruise flight, the pilot heard a “pop” sound followed by the engine accelerating to a high rpm. According to the pilot, the helicopter began spinning counterclockwise at a high rate; the cyclic stick would not move; and collective and pedal control inputs had no effect. The pilot continued his attempts to counteract the helicopter’s rotation as it descended to ground impact. Postaccident examination of the wreckage revealed that airframe damage was consistent with ground impact and that main rotor blade deformation and damage were consistent with powered impact with terrain. Damage to the tail rotor blades was consistent with the tail rotor not being under power at impact, and the tail rotor gearbox input pinion bevel gear was found fractured from its gear shaft. Metallurgical examination of the input pinion gear shaft revealed that it had fractured from fatigue. The fatigue cracking initiated at gouge marks on the outer surface of the cylindrical shaft and propagated through nearly the entirety of the shaft cross-section. The length of the fatigue cracks and the fine spacing of the striations were indicative of high cycle fatigue crack propagation. Review of maintenance records revealed that the tail rotor gearbox was disassembled, visually inspected, and reassembled about 330.3 hours before the accident. Based on the high cycle fatigue crack propagation and the presence of fatigue cracking on the majority of the fracture cross-section, it is likely the gouge marks on the input pinion gear shaft were created during reassembly of the tail rotor gearbox during this maintenance action. A loss of drive to the tail rotor would result in a clockwise, nose-right yaw of the helicopter due to the torque effect on the fuselage of the counterclockwise rotation of the main rotor. The sudden loss of tail rotor drive due to the fracture of the input pinion bevel gear would unload the powertrain of the power being used by the tail rotor, leading to a temporary increase of rotor rpm as well as engine rpm, consistent with the pilot’s report. Although the pilot reported that the helicopter began to spin counterclockwise, it is likely he misidentified the direction of yaw.
Probable cause
The improper reassembly of the tail rotor gearbox following maintenance, which resulted in fatigue failure of the input pinion gear shaft, and the subsequent loss of tail rotor drive.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ERA21LA386
- Event ID
- 20210929103994
- Case number
- ERA21LA386
- 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, cause areas. 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: e1a5df7c983bdfb468f7b03b0fcf25f8888a265ccaf3130941ef18bf41371c30; retrieved 2026-09-16T14:36:02.671Z.