NTSB Identification: LAX94LA075.
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Accident occurred Friday, December 10, 1993 in FLAGSTAFF, AZ
Probable Cause Approval Date: 10/20/1994
Aircraft: BELL 206B-III, registration: N2773R
Injuries: 2 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.

FOLLOWING AN ANNUAL INSPECTION, THE HELICOPTER HAD EXPERIENCED AN INTERMITTENT ILLUMINATION OF THE 'ENGINE OUT' ANNUNCIATOR LIGHT. THE PILOT CONTINUED FLYING AND MONITORED THE ENGINE INSTRUMENTS, PARTICULARLY THE N2 POWER TURBINE GAUGE. DURING THE ACCIDENT FLIGHT, THE ANNUNCIATOR AGAIN FLICKERED AND THEN STAYED ON. IN ADDITION, THE 'ENGINE OUT' HORN ALSO SOUNDED; HOWEVER, THE ENGINE PARAMETERS REMAINED NORMAL. THE ANNUNCIATOR LIGHT AND HORN WILL ACTIVATE IF THE N1 GAS PRODUCER FALLS BELOW 55 PERCENT. THE PILOT REPORTED THAT DURING A TURN, THE N2 BEGAN DECREASING AND HE ENTERED AN AUTOROTATION. THE HELICOPTER ROLLED OVER FOLLOWING A HARD LANDING. POSTACCIDENT TESTS REVEALED THAT THE ENGINE OPERATED WITHIN NORMAL SPECIFICATIONS. THE N2 TACH GENERATOR OPERATED NORMAL. THE N1 TACH GENERATOR FAILED.

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

The pilot's improper initiation of an emergency autorotation into unsuitable terrain and subsequent hard landing and rollover. A false annunciator indication, a failure of the N1 tach generator, the pilot's continued flight with a known aircraft defect, and the pilot's improper identification of the failed N1 gauge were factors in this accident.

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