# NTSB LAX92LA146: Hiller UH-12E, N93478, Huron, CA, March 21, 1992

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: March 21, 1992, 11:00 local (19:00 UTC)
- Place: Huron, CA
- Coordinates: 36.200187, -120.089965 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=36.2002&lon=-120.0900&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report August 26, 1993
- Report: Approved by Office Director
- Safety recommendations: Yes
- NTSB case key (mKey): 27578
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX92LA146
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27578/pdf
- Page: https://openairdocs.org/ntsb/LAX92LA146

## Probable cause

A SEPARATION OF THE CONTROL ROTOR CUFF DUE TO FATIGUE.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Airframe/component/system failure/malfunction, maneuvering
  - rotorcraft flight control - fatigue (cause)
  - rotorcraft flight control - separation (cause)
- Loss of control - in flight, maneuvering
- In flight collision with object, descent - emergency
  - object - tree(s)

## Analysis

THE PILOT EXPERIENCED A SUDDEN VIOLENT MAIN ROTOR VIBRATION WHILE ON A SPRAY RUN OVER AN ORCHARD.  WHILE MANEUVERING AT ABOUT 12 FEET ABOVE THE TREE TOPS, ONE OF THE CONTROL ROTOR BLADE ASSEMBLIES SEPARATED FROM THE ROTOR HUB.  AN EXAMINATION OF THE SEPARATED CONTROL ROTOR ASSEMBLY REVEALED A FATIGUE CRACK THAT ORIGINATED AT THE ROTOR CUFF RETAINING BOLT HOLE.  THE CONTROL ROTOR CUFF IS THE SUBJECT OF A 100-HOUR RECURRING INSPECTION AS A RESULT OF AN AIRWORTHINESS DIRECTIVE (AD).  THE AD WAS COMPLIED WITH DURING THE LAST 100-HOUR INSPECTION.  THE CUFF HAD ACCUMULATED 88.8 HOURS OF SERVICE SINCE THE LAST 100-HOUR INSPECTION.

## Aircraft

- Registration: [N93478](https://openairdocs.org/deregistered/N93478-2013-05-22), registration cancelled 2013-05-22, S/N 1608, built 1964 (OpenAirDocs)
- Reported make and model: HILLER UH-12E
- Registry model: [Hiller UH-12E](https://openairdocs.org/model/hiller-uh-12e) (registry code 4360122) (OpenAirDocs)
- Registry engine: [Lycoming VO-540 series](https://openairdocs.org/engine/lycoming-vo-540-series) (registry code 41534, reciprocating) (OpenAirDocs)
- Category: Helicopter
- Serial number: 1608
- Airframe hours: 5440
- Engines: LYCOMING VO-540-C2A 305 horsepower reciprocating
- Damage: Destroyed
- Flight: Aerial application, Part 137
- Operator: Huron Ag Helicopters Inc.
- Registered owner: Huron Ag Helicopters Inc.
- Airworthiness certificate: Special, Restricted (Special)
- Last inspection: 100 hour, September 22, 1991, 89 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 46; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: center; flight hours: 5,500 total, 4,000 in this make and model, 5,200 as pilot in command, 40 in the last 90 days, 40 in the last 30 days, 1 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 180° at 3 knots
- Visibility: 15 statute miles
- Lowest ceiling: none
- Temperature: 64 °F

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19920321007009A](https://openairdocs.org/incident/19920321007009A), Mar 21, 1992: Hiller UH12E, Huron, CA, Destroyed. Main rotor cuff failed due to fatigue cracking and corrosion. Helicopter settled into trees.

## Other investigations on N93478 (1)

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

- [NTSB LAX82FVG10](https://openairdocs.org/ntsb/LAX82FVG10), Dec 10, 1981: Hiller Acft UH-12E (N93478), Angels Camp, CA, substantial damage

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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