What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
The pilot exited the aircraft in order to escort a deplaning passenger. The student pilot rated passenger was left sitting in the aircraft, with instructions not to touch the controls. While the pilot was standing nearby, the aircraft began bouncing up and down in a resonant mode. He ran back to the aircraft and pulled the fuel flow control lever into the cut off position. The aircraft yawed to the right and settled back on the deck. An inspection of the aircraft revealed that the collective was not down and locked, nor were the frictions tightly applied. The manufacturer reported instances in which the collective lock was not seated properly and consequently released the collective while the engine was running. The fully down position of the collective is spring loaded to keep tension against the control lock. If the lock slips off collective, the spring's tension can force the control to move upward. No malfunctions or failures were found with the engine or rotor systems.
As the FAA filed it
THE PILOT EXITED THE AIRCRAFT IN ORDER TO ESCORT A DEPLANING PASSENGER. THE STUDENT PILOT RATED PASSENGER WAS LEFT SITTING IN THE AIRCRAFT, WITH INSTRUCTIONS NOT TO TOUCH THE CONTROLS. WHILE THE PILOT WAS STANDING NEARBY, THE AIRCRAFT BEGAN BOUNCING UP AND DOWN IN A RESONANT MODE. HE RAN BACK TO THE AIRCRAFT AND PULLED THE FUEL FLOW CONTROL LEVER INTO THE CUT OFF POSITION. THE AIRCRAFT YAWED TO THE RIGHT AND SETTLED BACK ON THE DECK. AN INSPECTION OF THE AIRCRAFT REVEALED THAT THE COLLECTIVE WAS NOT DOWN AND LOCKED, NOR WERE THE FRICTIONS TIGHTLY APPLIED. THE MANUFACTURER REPORTED INSTANCES IN WHICH THE COLLECTIVE LOCK WAS NOT SEATED PROPERLY AND CONSEQUENTLY RELEASED THE COLLECTIVE WHILE THE ENGINE WAS RUNNING. THE FULLY DOWN POSITION OF THE COLLECTIVE IS SPRING LOADED TO KEEP TENSION AGAINST THE CONTROL LOCK. IF THE LOCK SLIPS OFF COLLECTIVE, THE SPRING'S TENSION CAN FORCE THE CONTROL TO MOVE UPWARD. NO MALFUNCTIONS OR FAILURES WERE FOUND WITH THE ENGINE OR ROTOR SYSTEMS.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.