# NTSB LAX91LA249: Hiller UH-12E, N507HA, Huron, CA, June 7, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: June 6, 1991, 20:45 local (Jun 7, 1991, 03:45 UTC)
- Place: Huron, CA
- Coordinates: 36.200508, -120.090522 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=36.2005&lon=-120.0905&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report May 27, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 27237
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX91LA249
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27237/pdf
- Page: https://openairdocs.org/ntsb/LAX91LA249

## Probable cause

THAT UNKNOWN PILOT(S) IMPOPERLY USED THE THROTTLE CONTROL WHICH CAUSED AN OVERSPEED CONDITION.  CONTRIBUTING TO THIS ACCIDENT WAS THE CONNECTING ROD BOLT FATIGUE FAILURE.

## Sequence of events

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

- Loss of engine power, cruise
  - single engine aircraft
  - engine assembly,connecting rod bolt - failure,total (contributing factor)
  - engine assembly,connecting rod bolt - fatigue (contributing factor)
  - powerplant - overspeed (cause)
  - throttle/power control - improper use of, unknown (cause)
- Forced landing, descent - emergency
  - autorotation - performed, pilot in command
- In flight collision with object, descent - emergency
  - object - tree(s)

## Analysis

THE PILOT COMPLETED AN AERIAL APPLICATION FLIGHT AND WAS RETURNING TO THE LOADING AREA WHEN THE HELICOPTER SUSTAINED A TOTAL LOSS OF POWER.  DURING THE SUBSEQUENT AUTOROTATION THE PILOT ATTEMPTED TO SIDESLIP THE HELICOPTER BETWEEN THE ALMOND TREES BUT WAS UNABLE TO DO SO.  THE ENGINE AND SUBSEQUENT METALLURGICAL EXAMINATION DISCLOSED THE NO. 3 CYLINDER CONNECTING ROD BOLT FAILED DUE TO FATIGUE.  COMPANY MAINTENANCE PERSONNEL REPORTED THAT THE FATIGUE WAS CAUSED BY CONSISTENT ENGINE OVERSPEED POWER SETTINGS BY THE PILOTS FLYING THE HELICOPTER.

## Aircraft

- Registration: [N507HA](https://openairdocs.org/deregistered/N507HA-2013-03-21), registration cancelled 2013-03-21, S/N 5007, built 1976 (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: 5007
- Airframe hours: 3112
- Engines: LYCOMING VO-540-C2A 305 horsepower reciprocating
- Damage: Substantial damage
- Flight: Aerial application, Part 137
- Operator: San Joaquin Helicopters
- Registered owner: San Joaquin Helicopters
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, February 25, 1991, 114 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 43; commercial; airplane ratings: multi-engine land, single-engine land; medical: class 2, valid medical--no waivers/lim.; seat: center; flight hours: 15,000 total, 15,000 as pilot in command

## Weather

- Conditions: Visual (VMC), Night/bright
- Visibility: 20 statute miles
- Lowest ceiling: none
- Temperature: 70 °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 19910606020509A](https://openairdocs.org/incident/19910606020509A), Jun 6, 1991: Hiller UH12E, Huron, CA, Substantial damage. Returning to base after spraying. Engine failed at low altitude crashed into trees. Found broken connecting rod.

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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