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NTSB Report
March 21, 1992 · Hiller UH-12E · N93478
Huron, CA
Overview
Report Status
Probable Cause
Event Type
Accident
Date
March 21, 1992
Injury Outcomes
No injuries (1 uninjured)
Location
Huron, CA
Aircraft
Hiller UH-12E
Tail Number
N93478
Operator
Huron Ag Helicopters
Injuries
None
Aircraft Damage
Destroyed
NTSB Number
LAX92LA146
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.
NTSB Probable Cause
A SEPARATION OF THE CONTROL ROTOR CUFF DUE TO FATIGUE.
Full Narrative
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.
Flight
Event TypeAccident
Event Time11:00 PST
Nearest Airport0nm N
Runway0
Flight Plan FiledNone
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftHiller UH-12E
Tail NumberN93478
Aircraft CategoryHeli
DamageDestroyed
OperatorHuron Ag 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 46 · Second Class
Conditions
ConditionsVMC
LightDaylight
Wind180° @ 3 kt
Visibility15 sm
CeilingNone
Temperature / Dew Point64 F / 0 C
Altimeter0
Weather SourcePILO