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NTSB Report
August 25, 1991 · Hiller UH12D · N100HH
Sparks, NV
Overview
Report Status
Probable Cause
Event Type
Accident
Date
August 25, 1991
Injury Outcomes
No injuries (1 uninjured)
Location
Sparks, NV
Aircraft
Hiller UH12D
Tail Number
N100HH
Operator
Pathfinder Technology
Injuries
None
Aircraft Damage
Substantial
NTSB Number
LAX91LA369
THE CERTIFICATED PRIVATE HELICOPTER PILOT, THE SOLE OCCUPANT, WAS ON A LOCAL AREA FLIGHT WHEN A STRONG, MEDIUM TO HIGH FREQUENCY VIBRATION DEVELOPED IN THE TAIL SECTION OF HIS HELICOPTER. THE PILOT ELECTED TO MAKE A PRECAUTIONARY LANDING IN AN OPEN DIRT AREA, AND EXECUTED AN AUTOROTATION. AFTER TOUCHDOWN THE HELICOPTER SLID ON ROUGH, ROCKY TERRAIN, CAUSING THE MAIN ROTOR BLADES TO CONTACT THE TAIL BOOM. THREE FEET OF THE TAIL BOOM INCLUDING THE TAIL ROTOR GEAR BOX AND BLADES, AND THE TAIL ROTOR DRIVE SHAFT WERE SEVERED. AN EXAMINATION OF THE TAIL ROTOR DRIVE SHAFT AT THE POSITION WHERE A SUPPORT BEARING IS MOUNTED, REVEALED SIGNS OF HEAT AND WEAR. DURING THE IMPACT SEQUENCE, THE DRIVE SHAFT SUPPORT BEARING DEPARTED THE HELICOPTER AND WAS NOT RECOVERED.
NTSB Probable Cause
THE ENCOUNTER WITH ROUGH, UNSUITABLE TERRAIN DURING A PRECAUTIONARY LANDING. CONTRIBUTING TO THE ACCIDENT WAS THE PILOT'S DECISION TO MAKE AN AUTOROTATION AFTER ENCOUNTERING AN AIRFRAME VIBRATION.
Full Narrative
THE CERTIFICATED PRIVATE HELICOPTER PILOT, THE SOLE OCCUPANT, WAS ON A LOCAL AREA FLIGHT WHEN A STRONG, MEDIUM TO HIGH FREQUENCY VIBRATION DEVELOPED IN THE TAIL SECTION OF HIS HELICOPTER. THE PILOT ELECTED TO MAKE A PRECAUTIONARY LANDING IN AN OPEN DIRT AREA, AND EXECUTED AN AUTOROTATION. AFTER TOUCHDOWN THE HELICOPTER SLID ON ROUGH, ROCKY TERRAIN, CAUSING THE MAIN ROTOR BLADES TO CONTACT THE TAIL BOOM. THREE FEET OF THE TAIL BOOM INCLUDING THE TAIL ROTOR GEAR BOX AND BLADES, AND THE TAIL ROTOR DRIVE SHAFT WERE SEVERED. AN EXAMINATION OF THE TAIL ROTOR DRIVE SHAFT AT THE POSITION WHERE A SUPPORT BEARING IS MOUNTED, REVEALED SIGNS OF HEAT AND WEAR. DURING THE IMPACT SEQUENCE, THE DRIVE SHAFT SUPPORT BEARING DEPARTED THE HELICOPTER AND WAS NOT RECOVERED.
Flight
Event TypeAccident
Event Time19:50 PDT
Nearest Airport0nm N
Runway0
Flight Plan FiledNone
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftHiller UH12D
Tail NumberN100HH
Aircraft CategoryHeli
DamageSubstantial
OperatorPathfinder Technology
Operating RulePart 91
Engines1
Engine TypeReciprocating
Engine DetailsLycoming · VO-435-AIC · Reciprocating · 250
Seats3
People & Injuries
Injury SummaryNo injuries (1 uninjured)
Fatal0
Serious0
Minor0
Uninjured1
Total1
Crew 1Age 50 · Second Class
Conditions
ConditionsVMC
LightDusk
Wind270° @ 5 kt
Visibility10 sm
CeilingNone
Temperature / Dew Point0 C
Altimeter0
Weather SourcePILO