NTSB Identification: ANC95LA075.
The docket is stored in the Docket Management System (DMS). Please contact Records Management Division
Accident occurred Monday, June 12, 1995 in KETCHIKAN, AK
Probable Cause Approval Date: 02/08/1996
Aircraft: HUGHES 500D, registration: N549SW
Injuries: 4 Minor.

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

THE HELICOPTER PILOT WAS IN CRUISE FLIGHT ABOUT 250 FEET ABOVE THE GROUND, TRANSPORTING LOGGING PERSONNEL TO A REMOTE AREA. THE ENGINE SUDDENLY LOST POWER, AND THE PILOT BEGAN AN AUTOROTATION TO A GRAVEL PIT. DURING TOUCHDOWN, THE TAILBOOM WAS SEVERED, AND THE HELICOPTER ROLLED ONTO ITS RIGHT SIDE. DURING RECOVERY OF THE HELICOPTER, THE LIFTING CABLE BROKE, AND THE HELICOPTER DESCENDED TO THE GROUND FROM ABOUT 400 FEET. POSTACCIDENT EXAMINATION OF THE ENGINE FUEL CONTROL AND POWER TURBINE GOVERNOR DID NOT REVEAL ANY MALFUNCTION. EXAMINATION OF THE PNEUMATIC PC TUBE (AIR LINE) FROM THE PC FILTER TO THE GOVERNOR REVEALED AN AIR LEAK AT THE 'B' NUT ATTACHMENT TO THE GOVERNOR 'T' FITTING. LABORATORY TESTING REVEALED THAT A TORQUE OF 300 INCH POUNDS WOULD HAVE BEEN REQUIRED TO STOP THE AIR LEAK. THE MANUFACTURER'S SPECIFIED TORQUE VALUE WAS 100 INCH POUNDS. RECORDS SHOWED THAT ON 6/7/95, MAINTENANCE HAD BEEN PERFORMED TO REPLACE THE GOVERNOR AND TO CLEAN AND REINSTALL THE P2 AIR LINE; AND ON 6/11/95 (DAY BEFORE THE ACCIDENT), THE ENGINE SPEED HAD BEEN ADJUSTED. THE MAINTENANCE MANUAL FOR THE ENGINE WARNED THAT AIR LEAKS IN THE PNEUMATIC SENSING SYSTEM COULD RESULT IN FLAME-OUT, POWER LOSS, OR OVERSPEED.

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

AN AIR LEAK AT A 'B' NUT FITTING ON A PNEUMATIC PC TUBE TO THE POWER TURBINE GOVERNOR. COMPANY MAINTENANCE PERSONNEL DID NOT DETECT A LEAK AFTER PERFORMING MAINTENANCE ON THE GOVERNER AND P2 AIR LINE.

Full narrative available

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