NTSB Identification: LAX90LA137.
The docket is stored on NTSB microfiche number 44520.
Accident occurred Wednesday, April 04, 1990 in LA VERNE, CA
Probable Cause Approval Date: 03/12/1993
Aircraft: BELL 47G, registration: N739B
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.

ACCORDING TO THE INSTRUCTOR PILOT, THE AIRCRAFT BEGAN TO VIBRATE DURING TERMINATION OF A POWER RECOVERY AUTOROTATION. HE STATED THAT WHEN THE COMMERCIALLY RATED STUDENT PILOT APPLIED POWER, THE ENGINE DEVELOPED POWER, BUT THE ROTOR RPM DECAYED. THE AIRCRAFT COLLIDED WITH THE RUNWAY. THE INSTRUCTOR PILOT WAS LATE IN TAKING THE CONTROLS AND RECOVERING THE AIRCRAFT. AN FAA AIRWORTHINESS INSPECTOR EXAMINED THE HELICOPTER AND FOUND NO PRE-IMPACT MECHANICAL MALFUNCTIONS OR FAILURES.

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

THE HELICOPTER'S ROTOR SYSTEM BEING ALLOWED TO UNDERSPEED AS A RESULT OF IMPROPER USE OF FLIGHT CONTROLS BY THE DUAL STUDENT; IMPROPER SUPERVISION BY THE CERTIFIED FLIGHT INSTRUCTOR; AND DELAYED REMEDIAL ACTION BY THE CERTIFIED FLIGHT INSTRUCTOR WHICH ALLOWED THE IN FLIGHT COLLISION WITH THE RUNWAY.

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