NTSB Identification: SEA84LA153.
The docket is stored on NTSB microfiche number 25452.
Accident occurred Monday, July 02, 1984 in MT. ST. HELENS, WA
Probable Cause Approval Date: 03/04/1988
Aircraft: HUGHES 269C, registration: N58397
Injuries: 2 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.

THIS ACCIDENT OCCURRED AT THE 5500 FT LEVEL ON MT. ST. HELENS. DENSITY ALT AT THE TIME WAS 7500 FT. AT APRX 40-50 FT AGLENGINE AND ROTOR RPM BEGAN TO DECAY RAPIDLY. THE ACFT LANDED HARD ON A ROCK LEDGE WITH ONE SKID PARTIALLY OFF THE LEDGE.AS ROTOR RPM CONTINUED TO DECAY THE ROTOR DISC COULD NO LONGER SUPPORT THE HELICOPTER AND IT ROLLED 100 FT DOWN THE MOUNTAIN SUSTAINING SUBSTANTIAL DAMAGE. MAINTENANCE INVESTIGATION REVEALED THAT ALL SPARK PLUGS WERE SEVERLY WORN. WHEN TESTED, FOUR OUT OF EIGHT PLUGS FIRED INTERMITTENTLY. THE LEFT MAGNETO ALSO HAD BURNED POINTS.

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

IGNITION SYSTEM,SPARK PLUG..WORN

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

MAINTENANCE,INSPECTION..INADEQUATE..COMPANY MAINTENANCE PERSONNEL

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

IGNITION SYSTEM,MAGNETO..OUTPUT LOW



Contributing Factors

TERRAIN CONDITION..ROUGH/UNEVEN




Contributing Factors

TERRAIN CONDITION..DOWNHILL

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