Kona International Arpt Airport
Aircraft Accident/Incident Report

Kailua Kona, Hawaii 96740
Tuesady, October 29, 2013 17:20 HST

During the flight, the flight instructor moved the governor switch from the “automatic” to the “manual” position, which disengaged the full authority digital engine control governor, so that the pilot receiving instruction could practice manual throttle control using the twist grip on the collective. This was the first time that the pilot had flown this make and model of helicopter in the manual mode. When the pilot performed left and right 360-degree hovering turns, he found it difficult to rotate the twist grip but was able to manipulate it and maintain main rotor rpm (NR) within normal limits. The instructor then asked the pilot to perform a left, closed traffic pattern back to the departure airport. The pilot and the instructor reported that the takeoff, transition into cruise flight on the downwind leg, and initial descent were uneventful. The pilot reported that the helicopter was on final approach below 400 feet above ground level (agl) when he noticed that the NR was decreasing. He rotated the twist grip to increase power, but the NR continued to decrease. The low NR audio warning then sounded, and the instructor joined the pilot on the controls. The two pilots lowered the collective to enter an autorotation. The pilot said that the NR never recovered to the normal range even though the twist grip was rotated to its maximum (full-open) position. The flight instructor reported that the helicopter was about 200 to 300 feet agl when the NR began to decrease rapidly. The instructor stated that he took the controls and attempted to roll on more throttle but found that the throttle was already fully open. He said that he lowered the collective in an attempt to conserve NR. Both pilots reported that they pulled up on the collective to cushion the landing but that insufficient NR was remaining to slow the descent. The helicopter landed hard, slid forward on the taxiway, and yawed about 90 degrees left. The instructor reported that, when the helicopter came to a stop, the engine was not running, and the pilot reported that he was unaware of the engine’s status. Postaccident examination revealed no binding or other anomalies with the operation of the manual throttle control system or the throttle friction control wheel on the right (pilot’s side) collective. Neither the helicopter’s vehicle engine multifunction display nor its digital engine control unit recorded any faults for the accident flight. The engine was installed in a test cell, started, and tested in both automatic and manual governor modes, and no anomalies or uncommanded shutdowns were experienced, and the engine’s performance met the manufacturer’s specifications. Given the engine’s satisfactory performance during the postaccident test run and the lack of mechanical anomalies with the manual throttle control system, it is likely that the pilot receiving instruction mismanaged the twist grip throttle control during the approach, which led to a decay in NR. The instructor apparently did not notice the decay in NR until the low NR audio warning sounded, at which point, the helicopter was at too low an altitude to correct the situation.

The pilot receiving instruction’s failure to maintain main rotor rpm while practicing manual throttle control and the flight instructor’s delayed remedial action, which resulted in a hard landing.