NTSB Identification: SEA85FA134.
The docket is stored on NTSB microfiche number 30541.
Accident occurred Tuesday, June 11, 1985 in JUNEAU, AK
Aircraft: BELL UH-1B, registration: N99676
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

WHILE ENGAGED IN A LOG SLINGING OPERATION OVER MOUNTAINOUS, DENSELY FORESTED TERRAIN THE ROTOR CRAFT SUFFERED A TOTAL POWER LOSS FORCING THE PILOT TO EXECUTE AN AUTOROTATIVE LANDING INTO HIGH CONIFER TREES. DISASSEMBLY OF THE ENGINE REVEALED EVIDENCE THAT THE SPACER BETWEEN THE NO. 5 COMPRESSOR AND THE IMPELLER HAD NOT BEEN POSITION SEATED DURING THE LAST OVERHAUL AND THAT DURING THE ACCIDENT FLIGHT THE SPACER SLIPPED INTO ITS PROPER POSITION THUS RELEASING THE COMPRESSIVE TORQUE LOAD UNDER WHICH THE ASSEMBLY HAD BEEN SUFJECTED DURING BUILDIP. THE COMPRESSOR ASSEMBLY SUBSEQUENTLY BECAME UNCOUPLED FORCING THE IMPELLER FORWARD INTO ITS MAGNESIUM HOUSING. THIS ACTION RESULTED IN AN OVERTEMPERATURE CONDITION AND BREAKUP WITHIN THE TURBINE ASSEMBLY BROUGHT ON BY THE COMBUSTION OF MAGNESIUM PARTICLES.

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

COMPRESSOR ASSEMBLY..UNDERTORQUED

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

OBJECT..TREE(S)

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

MAINTENANCE,OVERHAUL..IMPROPER..OTHER MAINTENANCE PERSONNEL

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

COMPRESSOR ASSEMBLY,ROTOR DISC..UNLOCKED

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

COMPRESSOR ASSEMBLY,IMPELLER..DISCONNECTED


Contributing Factors

TERRAIN CONDITION..NONE SUITABLE

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