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NTSB Report
November 1, 1990 · Bell 47J-2 · N49DA
Gatlinburg, TN
Overview
Report Status
Probable Cause
Event Type
Accident
Date
November 1, 1990
Injury Outcomes
3 injuries (1 serious injury, 2 minor injuries)
Location
Gatlinburg, TN
Aircraft
Bell 47J-2
Tail Number
N49DA
Operator
Pigeon Forge Helicopters
Injuries
Serious
Aircraft Damage
Destroyed
NTSB Number
ATL91FA013
THE TWO PASSENGERS REPORTED THAT THEY HEARD A 'POP' SOUND, FOLLOWED BY THE HELICOPTER STARTING A CLOCKWISE SPIN TO THE RIGHT. THE HELICOPTER DESCENDED INTO THE TREES ON THE SIDE OF A STEEP SLOPE. INVESTIGATION REVEALED THAT THE TAIL ROTOR DRIVE SHAFT FAILED IMMEDIATELY FORWARD OF THE TAILBOOM EXTENSION TUBE. THE DRIVE SHAFT FAILED FROM FATIGUE CRACKING, PROPAGATING AT A HIGH RATE, SUGGESTING HIGH LOADS. THE T/R DRIVE SHAFT FORWARD BEARING HOUSING OUTER DIAMETER DIMENSION AND THE INNER DIAMETER OF THE TAILBOOM EXTENSION TUBE WERE WORN BEYOND REPLACEMENT LIMITS AND SHOULD HAVE BEEN REPLACED ACCORDING TO THE BELL MAINTENANCE AND OVERHAUL MANUAL. THE PASSENGER THREE-PLACE BENCH SEAT HAD BEEN ALTERED SO THAT THE INDIVIDUAL SEAT BELTS HAD BEEN MODIFIED INTO ONE SINGLE LONG BELT. THE BELT COULD BE OPENED ONLY ON THE LEFT SIDE OF THE BELT; THE BUCKLE ON THE RIGHT SIDE OF THE BELT WAS TAPED CLOSED WITH SILVER DUCT TAPE.
NTSB Probable Cause
THE ACCIDENT WAS INADEQUATE MAINTENANCE OF THE HELICOPTER, ALLOWING A TAIL ROTOR DRIVE SHAFT BEARING TO EXCEED WEAR LIMITS. THIS RESULTED IN HIGH LOADS ON THE TAIL ROTOR DRIVE SHAFT, AND THE RESULTING FATIGUE FAILURE OF THE DRIVE SHAFT.
Full Narrative
THE TWO PASSENGERS REPORTED THAT THEY HEARD A 'POP' SOUND, FOLLOWED BY THE HELICOPTER STARTING A CLOCKWISE SPIN TO THE RIGHT. THE HELICOPTER DESCENDED INTO THE TREES ON THE SIDE OF A STEEP SLOPE. INVESTIGATION REVEALED THAT THE TAIL ROTOR DRIVE SHAFT FAILED IMMEDIATELY FORWARD OF THE TAILBOOM EXTENSION TUBE. THE DRIVE SHAFT FAILED FROM FATIGUE CRACKING, PROPAGATING AT A HIGH RATE, SUGGESTING HIGH LOADS. THE T/R DRIVE SHAFT FORWARD BEARING HOUSING OUTER DIAMETER DIMENSION AND THE INNER DIAMETER OF THE TAILBOOM EXTENSION TUBE WERE WORN BEYOND REPLACEMENT LIMITS AND SHOULD HAVE BEEN REPLACED ACCORDING TO THE BELL MAINTENANCE AND OVERHAUL MANUAL. THE PASSENGER THREE-PLACE BENCH SEAT HAD BEEN ALTERED SO THAT THE INDIVIDUAL SEAT BELTS HAD BEEN MODIFIED INTO ONE SINGLE LONG BELT. THE BELT COULD BE OPENED ONLY ON THE LEFT SIDE OF THE BELT; THE BUCKLE ON THE RIGHT SIDE OF THE BELT WAS TAPED CLOSED WITH SILVER DUCT TAPE.
Flight
Event TypeAccident
Event Time14:00 EST
Nearest Airport0nm N
Runway0
Flight Plan FiledNone
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftBell 47J-2
Tail NumberN49DA
Aircraft CategoryHeli
DamageDestroyed
OperatorPigeon Forge Helicopters
Operating RulePart 91
Engines1
Engine TypeReciprocating
Engine DetailsLycoming · VO-540-B1B3 · Reciprocating · 260
Seats4
People & Injuries
Injury Summary3 injuries (1 serious injury, 2 minor injuries)
Fatal0
Serious1
Minor2
Uninjured0
Total3
Crew 1Age 43 · Second Class
Conditions
ConditionsVMC
LightDaylight
WindCalm
Visibility15 sm
CeilingNone
Temperature / Dew Point43 C
Altimeter30.00 inHg
Observation Time18:50
Weather SourceWFAC