TOLEDO, WA, USA
N8169J
BELL 47G3B2
WHILE LIFTING CHRISTMAS TREES UNDER EXTERNAL LOAD CONDITIONS THE PILOT HEARD A CLUNK AND EXPERIENCED A LOSS OF POWER. HE ATTEMPTED AN AUTOROTATION FROM 40 TO 50 FEET INTO THE CHRISTMAS TREE FARM, STRIKING AND BENDING THE TAIL BOOM WHEN IT IMPACTED A TREE. INVESTIGATION REVEALED THAT THE TRANSMISSION SHEAR BOLTS, PN 47-620-485-9, HAD SHEARED. THE PILOT ATTRIBUTED THE FAILURE OF THE SHEAR BOLTS TO POWER IMPULSES FROM REPEATED COMPRESSOR STALLS.
On November 9, 1993, at 0930, a Bell B-47G3B2, N8169J, operated by Farm & Forest Helicopter Service, impacted terrain at Toledo, Washington, during an emergency forced landing. There was no flight plan filed for the local external load flight, conducted under 14 CFR 133, that was on takeoff from a field site when the accident occurred. The commercial certificated pilot was not injured in the accident. The aircraft was substantially damaged. There was no fire. The pilot reported he was on takeoff with an external load of Christmas trees when he heard a grinding sound and the main rotor RPM began to decrease. He initiated an autorotation from about 40 to 50 feet into the christmas trees. On landing, the tair boot hit a tree and bent. An examination of the wreckage revealed fractured main transmission shear bolts. The pilot attributed the failure to power impulses after repeated compressor stalls or partial flame-outs of the turbine engine.
TRANSMISSION SHEAR BOLTS FAILED CAUSING A LOSS OF POWER TO THE ROTOR SYSTEM, AND THE PILOT ENCOUNTERED UNSUITABLE TERRAIN DURING HIS AUTOROTATION ATTEMPT.
Source: NTSB Aviation Accident Database
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