NTSB Identification: CHI89DEM09.
The docket is stored on NTSB microfiche number 41841.
Accident occurred Thursday, September 28, 1989 in HUDSONVILLE, MI
Probable Cause Approval Date: 06/30/1992
Aircraft: HILLER UH-12E, registration: N4028T
Injuries: 1 Minor.

APPROXIMATELY 10 MINUTES AFTER TAKEOFF AT AN ALTITUDE OF 300 FT AGL AND AN AIRSPEED OF 60 KTS, THE PILOT EXPERIENCED A SEVERE VIBRATION AND A DECREASE IN RESPONSE TO CONTROL INPUTS. THE PILOT ENTERED AN AUTOROTATION AND WHEN APPROXIMATELY 10 - 15 FT AGL, THE TAIL BOOM WAS SEPARATED BY THE MAIN ROTOR. THE HELICOPTER THEN DESCENDED, NOSE FIRST, TO TERRAIN IMPACT. INSPECTION REVEALED A TENSION-TORSION PIN HAD FAILED AT THE DRAG BRACE BOLT HOLE. PRE-EXISTING CRACKS WERE FOUND EXTENDING FROM THE PIN SHANK TO THE BOLT HOLE.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

THE FATIGUE FAILURE OF ONE OF THE TENSION-TORSION PINS.

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