THE PLT STATED THAT HE WAS FLYING STRAIGHT & LEVEL AT APRX 700 FT AGL, WHEN THE ENG-OUT LIGHT ILLUMINATED. HE BEGAN AN AUTOROTATION TO A RIDGELINE. DURING THE LANDING, THE MAIN ROTOR BLADES CONTACTED THE TAIL BOOM & SEVERED IT FROM THE MAIN FUSELAGE. AN INVESTIGATION REVEALED THAT THE ENG BURNER DRAIN VALVE HAD AN AIR LEAKAGE OF 3000 CC/MIN. THE MAX ALLOWABLE OHM LIMIT WAS 800 CC/MIN (AT 20 PSI). THE COMBUSTION LINER HAD EXCESSIVE HEAT DISTORTION ADJACENT TO THE LARGE DIAMETER HOLE ON THE RIGHT SIDE OF THE SKIRT. THE 1ST STAGE TURBINE NOZZLE HAD SEVERE HEAT DISTRESS ON 14 TRAILING EDGE VANES & 11 LEADING EDGE VANES. THE FUEL NOZZLE HAD HEAVY CARBON DEPOSITS ON THE SPRAY TIP & AIR SHROUD. ALSO, A WHITE RESIDUE WAS FOUND IN THE ENG & A FUEL SAMPLE REVERSED 425 PARTS PER MILLION OF PHOSPHORUS.

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

Contributing Factors

TERRAIN CONDITION..MOUNTAINOUS/HILLY

Contributing Factors

COMBUSTION ASSEMBLY,COMBUSTION LINER..DISTORTED

Contributing Factors

TURBINE ASSEMBLY,NOZZLE..OVERTEMPERATURE

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