CEN24LA027

On October 26, 2023, about 1652 central daylight time, a Robinson Helicopter R44, N141CD, was substantially damaged when it was involved in an accident near Rowlett, Texas. The flight instructor and pilot receiving instruction incurred minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor reported that the purpose of the flight was for the commercial rated pilot to receive instruction in basic IFR maneuvers, including holding at an RNAV fix and then performing an RNAV approach. The pilot was flying the helicopter, and the flight instructor was looking for other aircraft traffic in the area. While in level flight en route to the RNAV fix and maneuvering to avoid traffic, the flight instructor heard the engine and rotor rpm increase, followed by the high rotor rpm horn. The flight instructor took control of the helicopter, reduced the throttle, and subsequently observed another increase in engine and rotor rpm as if the throttle were fully open. The flight instructor again reduced the throttle, then observed rpm fluctuations. He reported observing fluctuations as high as 109 percent and as low as 95 percent in flight. He suspected they had a governor failure. He attempted overgripping the throttle but said it had limited effect in controlling the rpms. Concerned with the prospect that the engine could fail at any moment, the flight instructor initiated an autorotation, as the engine fluctuations could not affect flight if they were unmarried with the rotor. He observed a large dirt field off the nose of the helicopter and began their descent. The field had been recently plowed, and recent rain showers made the field muddy. During the touchdown on the field, the skids dug into the dirt and the helicopter nosed forward, which resulted in the main rotor contacting the ground. The helicopter spun violently and then came to rest. An onboard video and data recorder captured the entire flight. It began at 1636:12 with the flight instructor and student pilot conducting the preflight and helicopter engine start. At 1643:50, the helicopter departed to the south and then made a turn to the east. At 1649:24, the engine manifold pressure began to increase rapidly. The rpms increased from 100 to 110 percent and then began to fluctuate. At 1649:27, the flight instructor grabbed the cyclic and called for the controls. The student pilot’s hand remained on the cyclic. At 1649:31, the flight instructor let go of the cyclic and checked the warning light by pressing the press to test button. At 1649:38, the flight instructor repeated “My controls.” The student pilot confirmed “Your controls” while keeping a hand on the cyclic. At 1649:39, the flight instructor screamed “Let go” and the student pilot confirmed he was not touching the controls after letting go. The flight instructor was in control of the helicopter for the remainder of the flight. At 1650:02, the flight instructor stated“Oh yeah, actually that was not you. It was the governor.” At 1650:05, the flight instructor made a mayday call including that it was an “emergency engine out.” At 1650:47, the helicopter touched down, pitched forward and the main rotor struck the ground. Violent shaking began that lasted one minute and 25 seconds. At 1652:02, the flight instructor engaged the rotor brake, and the rotor stopped spinning 10 seconds later. The flight instructor and student pilot then exited the helicopter. The helicopter remained upright, but sustained substantial damage to the main rotor, tail rotor, tail boom, and empennage. The helicopter’s EMU/Governor Controller was retained for further examination. The EMU/Governor Controller was examined at the manufacturer’s facilities. The EMU/Governor Controller was a single unit, and it maintained the engine rpm in the governing range. Engine rpm and rotor rpm were related as long as the rotor is not in a freewheel/autorotation condition. The governor was active only above 80 percent engine rpm and could be switched on and off using the toggle switch on the end of the right seat collective. The EMU side of the unit just recorded data. Operational testing of the unit did not replicate the issue the flight crew experienced. The unit was opened, and the circuit board was examined. No anomalies were found that would have precluded the unit’s normal operation. No other preaccident malfunctions or failures with the helicopter were reported that would have precluded its normal operation. Per the helicopter’s Pilot Operating Handbook, the emergency procedure for a governor failure was to grip the throttle firmly to override the governor, then switch the governor off before completing the flight using the manual throttle control. The flight instructor reported that, although he thought that he attempted to disable the governor, post-flight he was not sure if they had accomplished it or not.