NTSB Identification: LAX91LA320.
The docket is stored on NTSB microfiche number 45292.
Accident occurred Sunday, July 21, 1991 in DAGGETT, CA
Probable Cause Approval Date: 04/08/1993
Aircraft: SIKORSKY SK-58, registration: N58WH
Injuries: 3 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

WHILE RETURNING FROM AN EXTERNAL LOAD OPERATION, THE HELICOPTER'S ENGINE STARTED VIBRATING AND THEN STARTED BACK FIRING. THE PILOT REPORTED HEARING A LOUD 'BANG' AND THEN NOTED A DECREASE IN ENGINE POWER. HE PERFORMED NECESSARY EMERGENCY PROCEDURES AND ENTERED AN AUTOROTATION. HE SAID THAT HE TOUCHED DOWN WITH SOME FORWARD SPEED. THE HELICOPTER HIT A DIRT BERM. THE ROTOR BLADES CONTACTED THE GROUND AND THE AIRCRAFT ROLLED OVER. AN ENGINE TEARDOWN WAS PERFORMED UNDER THE SUPERVISION OF AN FAA AIRWORTHINESS INSPECTOR. A BROKEN ROD WAS FOUND DURING THE TEARDOWN. THE TEARDOWN WAS TERMINATED AT THAT POINT AND THE REASON FOR THE BROKEN ROD WAS NOT DETERMINED.

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

THE FAILURE OF AN ENGINE CONNECTING ROD CAUSING A REDUCTION OF ENGINE POWER TO THE POINT WHERE LEVEL FLIGHT COULD NOT BE MAINTAINED. A FACTOR IN THE ACCIDENT WAS THE DARK NIGHT CONDITIONS WHICH RESTRICTED THE PILOT'S ABILITY TO SELECT THE BEST LANDING SITE.

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