What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Hard ground impact during practice autorotation. Fuel control governor surged and slow response in power recovery. (.4)the instructor pilot and new company pilot were practicing autorotations, which were terminating in a power-recovery. The flight instructor demonstrated a straight-in autorotation and said that the governor lagged behind but stayed in the green range. The instructor stated that this was typical of this particular helicopter and that he didn't consider the governor lag unusual. The instructor then had the dual student set up for a 180-degree autorotation. During the maneuver he told the student that he was ready to roll on the throttle at 200 feet AGL. He stated that at 50 feet and 50 to 55 knots, the pilot flared the helicopter and at 15 feet he had the pilot pull in more collective. At this point, the instructor pulled in some collective himself. He stated that the torque gauge did not move and that it sounded like the engine sound was dragging down and the rpm's in the dual tach decayed. The flight instructor proceeded to take the controls and leve l the aircraft. The aircraft landed hard and came to a complete stop. After the aircraft was shut down, the tail boom failure can occur in autorotations where touchdown occurs at 70 percent main rotor speed due to a resonance response to the structure to the main rotor. A postaccident test of the governor function was performed. Power checks were done to duplicate an autorotation and the tests revealed that the engine was slow to accelerate and tha governor surged with continual fluctuation of ng readings.
As the FAA filed it
HARD GROUND IMPACT DURING PRACTICE AUTOROTATION. FUEL CONTROL GOVERNOR SURGED AND SLOW RESPONSE IN POWER RECOVERY. (.4)THE INSTRUCTOR PILOT AND NEW COMPANY PILOT WERE PRACTICING AUTOROTATIONS, WHICH WERE TERMINATING IN A POWER-RECOVERY. THE FLIGHT INSTRUCTOR DEMONSTRATED A STRAIGHT-IN AUTOROTATION AND SAID THAT THE GOVERNOR LAGGED BEHIND BUT STAYED IN THE GREEN RANGE. THE INSTRUCTOR STATED THAT THIS WAS TYPICAL OF THIS PARTICULAR HELICOPTER AND THAT HE DIDN'T CONSIDER THE GOVERNOR LAG UNUSUAL. THE INSTRUCTOR THEN HAD THE DUAL STUDENT SET UP FOR A 180-DEGREE AUTOROTATION. DURING THE MANEUVER HE TOLD THE STUDENT THAT HE WAS READY TO ROLL ON THE THROTTLE AT 200 FEET AGL. HE STATED THAT AT 50 FEET AND 50 TO 55 KNOTS, THE PILOT FLARED THE HELICOPTER AND AT 15 FEET HE HAD THE PILOT PULL IN MORE COLLECTIVE. AT THIS POINT, THE INSTRUCTOR PULLED IN SOME COLLECTIVE HIMSELF. HE STATED THAT THE TORQUE GAUGE DID NOT MOVE AND THAT IT SOUNDED LIKE THE ENGINE SOUND WAS DRAGGING DOWN AND THE RPM'S IN THE DUAL TACH DECAYED. THE FLIGHT INSTRUCTOR PROCEEDED TO TAKE THE CONTROLS AND LEVE L THE AIRCRAFT. THE AIRCRAFT LANDED HARD AND CAME TO A COMPLETE STOP. AFTER THE AIRCRAFT WAS SHUT DOWN, THE TAIL BOOM FAILURE CAN OCCUR IN AUTOROTATIONS WHERE TOUCHDOWN OCCURS AT 70 PERCENT MAIN ROTOR SPEED DUE TO A RESONANCE RESPONSE TO THE STRUCTURE TO THE MAIN ROTOR. A POSTACCIDENT TEST OF THE GOVERNOR FUNCTION WAS PERFORMED. POWER CHECKS WERE DONE TO DUPLICATE AN AUTOROTATION AND THE TESTS REVEALED THAT THE ENGINE WAS SLOW TO ACCELERATE AND THA GOVERNOR SURGED WITH CONTINUAL FLUCTUATION OF NG READINGS.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.
Other reports on N8533F · 2
Matched to the same aircraft by N-number and date.