CHAMBLEE, GA, USA
N5745Y
BELL 206L-1
WHILE RETURNING TO REFUEL FROM AN AIR AMBULANCE FLIGHT THE HELICOPTER YAWED LEFT AND N2 DROPPED TO ABOUT 92% APPROXIMATELY ONE MILE FROM THE AIRPORT. AT 30-50 FEET WITH AIRSPEED AT ABOUT 20 KNOTS THE AIRCRAFT YAWED VIOLENTLY TO THE LEFT WITH CORRESPONDING DROPS IN N2 TO 55-60% THEN SURGED BACK TO 102-105%. THE PILOT ENTERED AUTOROTATION AND TOUCHED DOWN HARD 300 YARDS SHORT OF HIS INTENDED LANDING POINT. DETROIT DIESEL ALLISON COMMERCIAL ENGINE BULLETIN(CEB) A-73-2020 DATED 9/7/81 & REVISED 10/5/81 ADVOCATES DISARMING THE N2(ELECTRONIC) OVERSPEED CONTROL SYSTEM BECAUSE OF REPORTED INTERMITTENT AND SPURIOUS ACTIVATION OF THAT SYSTEM. THE SYSTEM WAS ONLY PARTIALLY DEACTIVATED IN COMPLIANCE WITH BELL ALERT SERVICE BULLETIN(ASB) 206L-81-24 DATED 9/11/81 DUE TO THE OPERATOR'S MAINTENANCE PERSONNEL REPORTING THAT THEY HAD NOT RECEIVED THE REFERENCED CEB AS OF THE DATE OF THE ACCIDENT.
Source: NTSB Aviation Accident Database
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