What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
(-23) The pilot was asked to perform an autorotation RPM check. He departed the helipad and transitional to an area normally used for practice manuevers about 12 miles south of Grand Junction, CO. Witness statements indicate he entered the autorotation manuever at about 2,000 feet AGL. Witness statements say they saw the rotor blades slow down and something move at the top of the helicopter. It then fell to the earth, exploded and burned. The pilot did not get out. Post-accident investigation revealed no evidence of mechanical failure. (.4) during a test flight, following maintenance on the helicopter, which required a functional flight check for vibration and autorotation, the helicopter was observed by witnesses to enter a rapid descent. During this maneuver, the rotor system was observed to slow down and the rotor blades to "fold" over the top of the helicopter. Pieces, which were later identified as fragments from the transmission cowling, were observed exiting the helicopter when the rotor system slowed down. The helicopter descended into the ground in a right hand turning maneuver. Examination of the wreckage revealed no evidence of either a structural or system failure or malfunction. According to the helicopter's manufacturer, as the main rotor system slows while under aerodynamic load, the main gear box can "walk" (horizontal orbital movement) on its mounting structure, which can result in contact between the transmission cowling and the main rotor control rod ends. Examination of the engines revealed evidence that engine power was applied when the rotor system was at low rotational speed. No evidence of preimpact engine failure or malfunction was found. According to available information, the pilot had received no training from the operator regarding the conduct of a maintenance test flight, not does the FAA require such training.
As the FAA filed it
(-23) THE PILOT WAS ASKED TO PERFORM AN AUTOROTATION RPM CHECK. HE DEPARTED THE HELIPAD AND TRANSITIONAL TO AN AREA NORMALLY USED FOR PRACTICE MANUEVERS ABOUT 12 MILES SOUTH OF GRAND JUNCTION, CO. WITNESS STATEMENTS INDICATE HE ENTERED THE AUTOROTATION MANUEVER AT ABOUT 2,000 FEET AGL. WITNESS STATEMENTS SAY THEY SAW THE ROTOR BLADES SLOW DOWN AND SOMETHING MOVE AT THE TOP OF THE HELICOPTER. IT THEN FELL TO THE EARTH, EXPLODED AND BURNED. THE PILOT DID NOT GET OUT. POST-ACCIDENT INVESTIGATION REVEALED NO EVIDENCE OF MECHANICAL FAILURE. (.4) DURING A TEST FLIGHT, FOLLOWING MAINTENANCE ON THE HELICOPTER, WHICH REQUIRED A FUNCTIONAL FLIGHT CHECK FOR VIBRATION AND AUTOROTATION, THE HELICOPTER WAS OBSERVED BY WITNESSES TO ENTER A RAPID DESCENT. DURING THIS MANEUVER, THE ROTOR SYSTEM WAS OBSERVED TO SLOW DOWN AND THE ROTOR BLADES TO "FOLD" OVER THE TOP OF THE HELICOPTER. PIECES, WHICH WERE LATER IDENTIFIED AS FRAGMENTS FROM THE TRANSMISSION COWLING, WERE OBSERVED EXITING THE HELICOPTER WHEN THE ROTOR SYSTEM SLOWED DOWN. THE HELICOPTER DESCENDED INTO THE GROUND IN A RIGHT HAND TURNING MANEUVER. EXAMINATION OF THE WRECKAGE REVEALED NO EVIDENCE OF EITHER A STRUCTURAL OR SYSTEM FAILURE OR MALFUNCTION. ACCORDING TO THE HELICOPTER'S MANUFACTURER, AS THE MAIN ROTOR SYSTEM SLOWS WHILE UNDER AERODYNAMIC LOAD, THE MAIN GEAR BOX CAN "WALK" (HORIZONTAL ORBITAL MOVEMENT) ON ITS MOUNTING STRUCTURE, WHICH CAN RESULT IN CONTACT BETWEEN THE TRANSMISSION COWLING AND THE MAIN ROTOR CONTROL ROD ENDS. EXAMINATION OF THE ENGINES REVEALED EVIDENCE THAT ENGINE POWER WAS APPLIED WHEN THE ROTOR SYSTEM WAS AT LOW ROTATIONAL SPEED. NO EVIDENCE OF PREIMPACT ENGINE FAILURE OR MALFUNCTION WAS FOUND. ACCORDING TO AVAILABLE INFORMATION, THE PILOT HAD RECEIVED NO TRAINING FROM THE OPERATOR REGARDING THE CONDUCT OF A MAINTENANCE TEST FLIGHT, NOT DOES THE FAA REQUIRE SUCH TRAINING.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.