Accident Overview
On January 24, 2023, about 1300 Pacific standard time, a Kaman Aerospace Corp K-1200 helicopter, registration N202WM, was substantially damaged when it experienced a loss of engine power during a logging operation near Sweet Home, Oregon. The pilot, who was the sole occupant, was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 133 as an external load operation.
Flight History
The helicopter had recently been fitted with an overhauled engine. On the day before the accident, the pilot noticed a slower-than-normal governor response when increasing power. He returned to the landing area and discussed the issue with a mechanic. The mechanic inspected the engine and made an adjustment, after which the pilot flew for 2.3 hours without further incident. However, he later heard a "rushing air" sound while landing a log. Again returning to the landing area, both pilot and mechanic confirmed the bleed band function and made another adjustment. A ground run confirmed the adjustment, and operations ceased for the night.
The next day, during the accident flight, the helicopter sustained a loss of engine power when the pilot added power while placing a log in the landing zone. Unable to maintain altitude, the pilot performed a forced landing onto open terrain. As the helicopter descended, the landing gear struck cut logs, causing the helicopter to roll down a hill and come to rest inverted.
Video Recordings
The helicopter was equipped with an Appareo AIRS-400 video recorder, which captured an over-shoulder view of the pilot and most of the instrument panel. The recording lasted about 15 minutes. It showed the helicopter picking up a log, with the load meter appearing inoperative and the red torque warning light flickering. At about 1 minute 57 seconds into the recording, the engine noise changed, consistent with a reduction in main rotor rpm (droop). The helicopter pitched nose-down, and engine instruments showed the dual tachometer decaying from about 104% Nr, exhaust gas temperature (EGT) rising from about 550-600°C, and no caution lights. The rotor rpm light illuminated at about 2 minutes 3 seconds and remained on. At about 2 minutes 6 seconds, the helicopter was descending with the dual tach at about 80% Nr, N1 at about 85%, and EGT at about 950-1000°C. The helicopter impacted terrain at about 2 minutes 18 seconds and rolled onto its right side. The pilot was assisted out of the cockpit by ground personnel at about 3 minutes 5 seconds.
Wreckage and Engine Examination
Postaccident examination revealed that the fuselage was mostly intact, with crushing and bending on the nose, bottom, and upper fuselage. Flight control continuity was established for both cyclic and collective controls. The fuel system was intact; fuel expelled from the engine attachment fitting when the boost pumps were turned on. Fuel samples tested negative for water. The engine was removed and examined. The GP (gas producer) spool rotated smoothly, but the power turbine (PT) could not be turned. Internal examination found the 2nd stage GP nozzle thermally damaged and the 2nd stage GP turbine blades fractured unevenly without evidence of fatigue. The PT assembly exhibited impact damage. The bleed band and actuator functioned normally. Testing of the power turbine governor (PTG) revealed random intermittency; it failed the functional test. Further examination found that the locking feature for the adjusting screw on the N2 topping governor lever and roller assembly was incorrectly clamped, allowing the adjusting screw to rotate and change position. The source states that this inconsistent behavior can cause the PTG to inappropriately open the transient air-bleed control valve, which opens the bleed band actuator valve, allowing compressor air to escape and turbines to overheat—consistent with the observed thermal damage.