What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Aircraft was flying southbound at or about 600 feet. Pilot stated he heard a loud ?pop? That was accompanied by a yaw of the aircraft and noticed vibration and or roughness of the engine. The rotor tachometer gauge was indicating zero rotor RPM and the engine tachometer indicated below 70%. Pilot entered autorotation and at touchdown aircraft rolled up on the forward skids and pilot applied aft cyclic. Main rotor blades contacted tailboom and chopped the boom off forward of the tailrotor gearbox. Post-accident inspection revealed the main gearbox yoke part number C908-1 was missing one of two magnets. The two factory installed magnets provide the signal for the main rotor tachometer and the loss of a magnet from this yoke will disrupt main rotor RPM indication in the cockpit of the helicopter.
As the FAA filed it
AIRCRAFT WAS FLYING SOUTHBOUND AT OR ABOUT 600 FEET. PILOT STATED HE HEARD A LOUD ?POP? THAT WAS ACCOMPANIED BY A YAW OF THE AIRCRAFT AND NOTICED VIBRATION AND OR ROUGHNESS OF THE ENGINE. THE ROTOR TACHOMETER GAUGE WAS INDICATING ZERO ROTOR RPM AND THE ENGINE TACHOMETER INDICATED BELOW 70%. PILOT ENTERED AUTOROTATION AND AT TOUCHDOWN AIRCRAFT ROLLED UP ON THE FORWARD SKIDS AND PILOT APPLIED AFT CYCLIC. MAIN ROTOR BLADES CONTACTED TAILBOOM AND CHOPPED THE BOOM OFF FORWARD OF THE TAILROTOR GEARBOX. POST-ACCIDENT INSPECTION REVEALED THE MAIN GEARBOX YOKE PART NUMBER C908-1 WAS MISSING ONE OF TWO MAGNETS. THE TWO FACTORY INSTALLED MAGNETS PROVIDE THE SIGNAL FOR THE MAIN ROTOR TACHOMETER AND THE LOSS OF A MAGNET FROM THIS YOKE WILL DISRUPT MAIN ROTOR RPM INDICATION IN THE COCKPIT OF THE HELICOPTER.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.