NTSB Identification: ANC89FA069.
The docket is stored on NTSB microfiche number 40054.
Nonscheduled 14 CFR
Accident occurred Saturday, May 06, 1989 in GIRDWOOD, AK
Probable Cause Approval Date: 08/02/1990
Aircraft: BELL 412, registration: N524EH
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.

WHILE IFR AT 10,000 FEET OVER MOUNTAINOUS TERRAIN, THE HELCIOPTER EXPERIENCED VIOLENT VERTICAL VIBRATIONS, WHICH CONTINUED UNTIL THE CRASH-LANDING ABOUT FIVE MINUTES LATER. ON BOARD WEATHER RADAR WAS USED TO GUIDE THE HELICOPTER AROUND THE MOUNTAIN TOPS, WHICH WERE IN THE CLOUDS. AT ABOUT 200 FEET ABOVE THE GROUND, THE HELICOPTER CAUGHT FIRE, TAIL ROTOR CONTROL WAS LOST, BOTH ENGINES QUIT, AND CYCLIC CONTROL BECAME UNRESPONSIVE. THE HELICOPTER WAS DESTROYED BY POST-CRASH FIRE. ABOUT ONE HOUR OF FLT TIME EARLIER, THE HELICOPTER HAD UNDERGONE AN INSPECTION, DURING WHICH THE MAIN ROTOR FLIGHT CONTROL SYSTEM BOLTS HAD BEEN RETORQUED. ALL BUT ONE OF THESE BOLTS WERE FOUND IN THE WRECKAGE. HOWEVER, THE ROD END FOR THE MISSING BOLT WAS FOUND.

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

A MAIN ROTOR FLIGHT CONTROL BOLT (PART NUMBER 20-057-6-38D) CAME OUT OF ITS ROD END BEARING WHILE IN FLIGHT DUE TO THE BOLT BEING IMPROPERLY TORQUED DURING MAINTENANCE.

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