N202WM

On January 24, 2023, about 1300 Pacific standard time, a Kaman Aerospace Corp, K-1200 helicopter, N202WM, was substantially damaged when it was involved in an accident near Sweet Home, Oregon. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 133 external load flight.

The pilot reported that an overhauled engine had recently been installed in the helicopter. On the day before the accident flight, while conducting logging operations, he experienced what seemed to be a slower than normal governor response (governor lag) to an increase in power. Concerned, he returned to the service landing area, shut down the helicopter, and addressed his concerns with the mechanic.

The mechanic proceeded to check over the engine to try find any possible discrepancies that could have led to the irregularity. The mechanic made an adjustment and the pilot returned to flying for 2.3 uneventful hours until he heard “rushing air” while landing a log. He immediately returned to the service landing and consulted the mechanic. They confirmed the bleed band function, and the mechanic made an adjustment. They performed a ground run to confirm the adjustment did what they wanted it to and ended operations for the night.

The following day, during the accident flight, the helicopter sustained a loss of engine power when the pilot added power while laying a log into the log landing zone. Unable to maintain altitude, the pilot elected to make a forced landing onto open terrain. As the helicopter descended toward the open terrain, the landing gear impacted cut logs and the helicopter rolled down a hill and came to rest inverted.

A review of maintenance records revealed that engine was replaced on January 16, 2023. On January 23, 2023, an adjustment was made to the fuel control unit (FCU) and bleed band.

The helicopter was equipped with an Appareo AIRS-400 video recording device that provided an over-shoulder view of the front seat and most of the helicopter’s instrument panel. The device was sent to the National Transportation Safety Board Vehicle Recorders Division for examination. The examination revealed that the device appeared undamaged and was otherwise intact. The device had two memory storage devices: a removable SD card and internal memory. The removable SD card was found to be in good condition and the recorded video files were downloaded.

The recorded video files began with an over-shoulder view of the pilot operating the helicopter. Most of the instrument panel was captured, as well as a view out of the windscreen. The pilot’s cyclic movements were captured; however, the collective’s movements were not captured. The recording time totaled about 15 minutes.

The video began as the helicopter was transitioning from the landing area to the pick-up site (logging area). The instruments indicated the helicopter did not have a log attached to the long line, and no caution or warning lights were noted on the instrument panel. At about 00:59 (all times listed from the beginning of the recording), the flight operation was consistent with the helicopter picking up a log, the load meter appeared to be inoperative, and the red torque warning light flickered. The pilot appeared to maneuver the helicopter within the pick-up area with a log. The engine instruments appeared normal and the helicopter transitioned to forward flight.

At about 01:55 the helicopter arrived near the log landing zone and came to a hover. At about 01:57, the audio of the engine noise changed significantly and appeared consistent with a reduction in main rotor rpm (droop). The helicopter’s nose pitched down abruptly, and the following was noted on the engine instrument panel: dual tach was at about 104% Nr and started to quickly decay, EGT was at about 550 – 600 deg C and rising, no caution or warning lights were noted. In the following seconds, the sound associated with the rotor rpm continued to decay and an abrupt aft pitch was noted. At about 02:03, the rotor rpm light illuminated and remained illuminated for the remainder of the recording. At about 02:06, the helicopter was descending and the following was noted on the engine instrument panel: dual tach was at about 80% Nr and still decaying, N1 was at about 85%, EGT was at about 950 -1000 deg C and rising. At about 02:18 the helicopter impacted terrain and rolled onto its right side. Multiple annunciator lights were illuminated on the instrument panel. At about 03:05 the pilot was assisted in exiting the cockpit and out of the right door by unseen ground personnel. The recording ended at 05:05.

Postaccident examination of the recovered wreckage revealed that the fuselage was mostly intact. Crushing and bending was observed on the nose compartment. Crushing and bending was observed on the bottom and upper fuselage.

Cyclic flight control continuity was established from the cockpit to the L-cranks. Collective flight control continuity was established from the cockpit to the L-cranks, engine governor, and the horizontal stabilizer.

A visual inspection of the fuel system was conducted and continuity was established from the main fuel tank throughout the system to the engine. External power was applied to the airframe; when both the forward and aft airframe electric boost fuel pumps were turned on, fuel expelled from engine attachment fuel fitting. A visual inspection of the airframe fuel filter revealed minor debris. Fuel samples were taken from the fuel sump and the airframe fuel filter. The fuel was tested for water using SAR-GEL water finding paste, with negative results.

The engine was attached to the helicopter via the airframe engine mounts. No visible damage was observed or noted to the exterior of the engine. The engine was removed and mounted on an engine stand. The GP or N1 spool could be smoothly rotated by hand with no noise or grinding. The power turbine (PT) could not be turned. The engine was removed for further examination.

Subsequent examination of the engine revealed the 1st stage GP nozzle and turbine were intact and undamaged. The 2nd stage GP nozzle was intact; however, it was thermally damaged. The 2nd stage GP turbine blades were all fractured in an uneven pattern near the ½ to ¾ span. No evidence of fatigue was found in any of the blade fracture surfaces.

The PT assembly was intact but exhibited impact damage to the 1st and 2nd stage nozzles and rotors.

The bleed band was intact and undamaged. The bleed band actuator was removed and functionally tested with no anomalies found.

Testing of the PTG using the factory functional test procedure resulted in the PTG exhibiting a random intermittency and failing the test.

Further examination of the PTG revealed the locking feature for the adjusting screw on the N2 topping governor lever and roller assembly was incorrectly clamped. The adjusting screw had rotated in the threaded portion of the lever assembly and was no longer in the correct original location. The incorrectly locked clamp screw of the allowed for unpredictable, large inconsistencies in the feedback lever position.

Figure 1: View of the N2 Topping Governor Lever and Adjustment Screw (With Spherical End) Assembly.

The inconsistent behavior of the N2 topping governor lever and roller assembly adjusting screw can cause the PTG to inappropriately open the transient air-bleed control valve, which in turn opens the bleed band actuator valve, allowing compressor air to escape and the turbines to overheat due to the loss of cooling air, as was observed during the engine core examination.

A review of the PTG component card revealed that the PTG had been overhauled and functionally tested in August of 2018. A subsequent inspection was conducted in April of 2020 when the PTG was installed on the accident engine. The component card indicates that at the time the engine was installed in the accident helicopter, the PTG time since overhaul was about 1875 hours.