NTSB Identification: ANC93FA061.
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Accident occurred Saturday, May 08, 1993 in THORNE BAY, AK
Probable Cause Approval Date: 09/30/1994
Aircraft: BELL 214B1, registration: N314CR
Injuries: 2 Minor.
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.
THE HELICOPTER WAS BEING USED TO MOVE LOGS IN A LONG-LINE LIFT OPERATION. THE PILOT REPORTED THAT AS HE INCREASED COLLECTIVE TO LIFT A LOG, HE HEARD A LOUD NOISE, WHICH WAS FOLLOWED BY A LOSS OF POWER. AN AUTOROTATION WAS MADE TO A LANDING ON ROUGH, DOWNHILL TERRAIN, DOWNSLOPE FROM WHERE THE LOG WAS BEING LIFTED. A TEARDOWN OF THE ENGINE REVEALED EVIDENCE OF FOREIGN OBJECT DAMAGE AT THE 6TH AND 7TH STAGES OF THE N1 (GAS PRODUCER) COMPRESSOR. SELF-LOCKING NUTS (PN STD3064-4) WERE MISSING FROM 2 COMPRESSOR CASE BOLTS (PN MS9566-36), WHICH WERE LOCATED OVER A BLEED PORT, LEADING TO THE 6TH STAGE OF THE GAS PRODUCER. METALLURGICAL EXAM REVEALED NUT FRAGMENTS OF A CHEMICAL COMPOSITION, CONSISTENT WITH THE MATERIAL SPECIFIED IN STD3064-4 NUTS. THE ENGINE HAD BEEN IN OPERATION ABOUT 283 HOURS, AFTER BEING REASSEMBLED WITH A NEW COMPRESSOR SECTION.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: FOREIGN OBJECT DAMAGE TO THE COMPRESSOR ASSEMBLY, PROBABLY DUE TO LOOSE NUTS FROM THE COMPRESSOR CASE AFTER IMPROPER MAINTENANCE (INSTALLATION) BY MAINTENANCE PERSONNEL. Full narrative available
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