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NTSB Report
June 7, 1991 · Hiller UH-12E · N507HA
Huron, CA
Overview
Report Status
Probable Cause
Event Type
Accident
Date
June 7, 1991
Injury Outcomes
No injuries (1 uninjured)
Location
Huron, CA
Aircraft
Hiller UH-12E
Tail Number
N507HA
Operator
San Joaquin Helicopters
Injuries
None
Aircraft Damage
Substantial
NTSB Number
LAX91LA249
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.
NTSB 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.
Full Narrative
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.
Flight
Event TypeAccident
Event Time20:45 PDT
Nearest Airport0nm N
Runway0
Flight Plan FiledNone
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftHiller UH-12E
Tail NumberN507HA
Aircraft CategoryHeli
DamageSubstantial
OperatorSan Joaquin Helicopters
Operating RulePart 137
Engines1
Engine TypeReciprocating
Engine DetailsLycoming · VO-540-C2A · Reciprocating · 305
Seats3
People & Injuries
Injury SummaryNo injuries (1 uninjured)
Fatal0
Serious0
Minor0
Uninjured1
Total1
Crew 1Age 43 · Second Class
Conditions
ConditionsVMC
LightBright Night
WindCalm
Visibility20 sm
CeilingNone
Temperature / Dew Point70 F / 0 C
Altimeter0
Weather SourcePILO