NTSB Identification: LAX95LA158.
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Accident occurred Tuesday, April 11, 1995 in LAKEPORT, CA
Probable Cause Approval Date: 09/24/1995
Aircraft: ROBINSON R-22B, registration: N4015Y
Injuries: 1 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 STUDENT WAS DOING TAKEOFFS AND LANDINGS IN THE TRAFFIC PATTERN WHEN THE LOW ROTOR RPM WARNING HORN ACTIVATED. THE STUDENT WAS UNSUCCESSFUL IN EXTINGUISHING THE WARNING HORN BY THROTTLE AND COLLECTIVE MANIPULATION AND ENTERED AN AUTOROTATION. THE STUDENT DID NOT VERIFY THE MAIN ROTOR RPM BY THE ROTOR TACHOMETER. DURING THE TOUCHDOWN, ABOUT 1/4-MILE SOUTHEAST OF THE AIRPORT IN A SOFT FIELD, THE SKIDS DUG INTO SOFT SOIL AND THE HELICOPTER ROLLED OVER. A FAA INSPECTOR EXAMINED THE AIRCRAFT AND ENGINE, WHICH INCLUDED AN ENGINE START AND STATIC RUN-UP. THE ENGINE STARTED NORMALLY AND WAS EXERCISED THROUGHOUT ITS NORMAL POWER RANGE. MAINTENANCE RECORDS REVEALED A HISTORY OF FALSE LOW ROTOR RPM WARNING HORN ACTIVATIONS IN THE HELICOPTER DATING BACK 9 MONTHS. AFTER PILOTS WOULD REPORT THE WARNING HORN DISCREPANCY TO MAINTENANCE PERSONNEL, A SYSTEM COMPONENT WOULD BE CHANGED AND THE HELICOPTER RETURNED TO SERVICE; HOWEVER, THE PROBLEM PERSISTED. THE CFI'S SAID THEY TRAINED THE STUDENTS, INCLUDING THE ACCIDENT PILOT, HOW TO COPE WITH THE NUISANCE WARNING.

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

the student's misjudged landing flare and his failure to verify the validity of the low rotor warning. Factors in the accident were the company management's continued use of the helicopter in flight training operations with a known discrepancy in the main rotor warning system, and the soft nature of the soil at the autorotation landing area.

Full narrative available

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