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NTSB Report
August 12, 1987 · Bell 206B · N33PW
Pledger, TX
Overview
Report Status
Preliminary report
Event Type
Accident
Date
August 12, 1987
Injury Outcomes
No injuries (4 uninjured)
Location
Pledger, TX
Aircraft
Bell 206B
Tail Number
N33PW
Operator
Houston Helicopters
Injuries
None
Aircraft Damage
Substantial
NTSB Number
FTW87FA198
WHILE CRUISING AT 900' AGL, THE PLT NOTED A HVY SHUDDER FLWD BY A GRINDING NOISE, LOUD 'BANG' & A LOW ROTOR RPM SIGNAL. HE MADE AN AUTOROTATION TO A ROAD, BUT DRG TOUCHDOWN, THE MAIN ROTOR BLADES FLEXED DWN & SEVERED THE TAIL BOOM. AN EXAM REVEALED THE MAIN PWR (SHORT) SHAFT HAD FAILED DUE TO MISALIGNMENT & HI TEMPS RESULTING FROM THE MISALIGNMENT. FURTHER INV SHOWED THAT THE MISALIGNMENT WAS THE RESULT OF A FAILURE OF THE PYLON ISOLATOR MOUNT DUE TO DEBONDING BETWEEN THE UPPER PLATE & THE RUBBER DAMPER ELEMENT. DEBONDING OCCURRED AFTER PROLONGED EXPOSURE OF THE ISOLATOR MOUNT TO OIL & GREASE WHICH CHEMICALLY DETERIORATED THE BOND. THERE WAS EVIDENCE THE DETERIORATION HAD OCCURRED OVER A LONG PERIOD OF TIME. THE UNIT HAD BEEN INSPECTED PERIODICALLY, BUT THE IMPENDING FAILURE OF THE BOND HAD NOT BEEN DETECTED.
Full Narrative
WHILE CRUISING AT 900' AGL, THE PLT NOTED A HVY SHUDDER FLWD BY A GRINDING NOISE, LOUD 'BANG' & A LOW ROTOR RPM SIGNAL. HE MADE AN AUTOROTATION TO A ROAD, BUT DRG TOUCHDOWN, THE MAIN ROTOR BLADES FLEXED DWN & SEVERED THE TAIL BOOM. AN EXAM REVEALED THE MAIN PWR (SHORT) SHAFT HAD FAILED DUE TO MISALIGNMENT & HI TEMPS RESULTING FROM THE MISALIGNMENT. FURTHER INV SHOWED THAT THE MISALIGNMENT WAS THE RESULT OF A FAILURE OF THE PYLON ISOLATOR MOUNT DUE TO DEBONDING BETWEEN THE UPPER PLATE & THE RUBBER DAMPER ELEMENT. DEBONDING OCCURRED AFTER PROLONGED EXPOSURE OF THE ISOLATOR MOUNT TO OIL & GREASE WHICH CHEMICALLY DETERIORATED THE BOND. THERE WAS EVIDENCE THE DETERIORATION HAD OCCURRED OVER A LONG PERIOD OF TIME. THE UNIT HAD BEEN INSPECTED PERIODICALLY, BUT THE IMPENDING FAILURE OF THE BOND HAD NOT BEEN DETECTED.
Flight
Event TypeAccident
Event Time16:20 CDT
Nearest Airport0nm N
Runway0
Runway Length0
Runway Width0
Flight Plan FiledCvfr
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftBell 206B
Tail NumberN33PW
Aircraft CategoryHeli
DamageSubstantial
OperatorHouston Helicopters
Operating RulePart 135
Engines1
Engine TypeTurboshaft
Engine DetailsAllison · 250-C20B · Turboshaft · 317
Seats5
People & Injuries
Injury SummaryNo injuries (4 uninjured)
Fatal0
Serious0
Minor0
Uninjured4
Total4
Crew 1Age 45 · Second Class
Conditions
ConditionsVMC
LightDaylight
Wind180° @ 6 kt
Visibility10 sm
CeilingNone
Temperature / Dew Point70 F
Altimeter29.00 inHg
Observation Time20:52
Weather SourceWFAC