NTSB Identification: LAX92LA214.
The docket is stored on NTSB microfiche number 46126.
Accident occurred Friday, May 22, 1992 in GLENDALE, AZ
Probable Cause Approval Date: 09/28/1993
Aircraft: COBB INTL EXEC 90, registration: N7656T
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.

THE FLIGHT DEPARTED THE AIRPORT ON A LOCAL INSTRUCTIONAL FLIGHT. WHEN THE FLIGHT RETURNED TO THE AIRPORT THE CFI INSTRUCTED THE NONCERTIFICATED STUDENT PILOT TO EXECUTE A SIMULATED ENGINE OUT AUTOROTATION. THE STUDENT PILOT ENTERED THE AUTOROTATION AT A LOW MAIN ROTOR RPM, BUT DURING THE DESCENT THE RPM INCREASED TO THE LOW SIDE OF ITS NORMAL OPERATING RANGE. THE CFI ATTEMPTED TO TERMINATE THE AUTOROTATION AT 200 FEET AGL BECAUSE OF THE MARGINAL LOW ROTOR RPM, BUT WHEN HE APPLIED RAPID FULL THROTTLE THE ENGINE FALTERED AND THEN FAILED. THE CFI EXECUTED AN EMERGENCY AUTOROATIVE LANDING. ON TOUCHDOWN THE HELICOPTER BOUNCED, THE SKIDS DUG INTO THE SOFT DIRT ON THE SECOND TOUCHDOWN AND THE HELICOPTER CAME TO AN ABRUPT STOP AND ROLLED OVER. THE POST ACCIDENT ENGINE EXAMINATION DISCLOSED THAT THE ENGINE OPERATED NORMALLY THROUGHOUT ITS NORMAL OPERATIONAL PARAMETERS BUT WHEN THE THROTTLE WAS RAPIDLY APPLIED AFTER A PROLONGED IDLE THE ENGINE FALTERED. THE IDLE RPM WAS MARGINAL AND THE CARBURETOR HAD RECENTLY BEEN REPLACED.

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

THE IMPROPER CARBURETOR IDLE ADJUSTMENT BY COMPANY MAINTENANCE PERSONNEL. CONTRIBUTING TO THIS ACCIDENT WAS THE CFI'S INABILITY TO ATTAIN ADEQUATE RPM AND THE SOFT DIRT.

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