History of Flight
On May 11, 2022, at about 0930 Pacific daylight time, a Bell Helicopter Textron Canada 407, registered N999GH, was substantially damaged during an accident near Livermore, California. The pilot was seriously injured, and a lineman crew member sustained minor injuries. The helicopter was being operated as a Title 14 Code of Federal Regulations Part 133 rotorcraft external-load flight.
The pilot was conducting a helicopter external load (HEC) long-line qualification exam flight at the Livermore Electric Safety Academy, a training facility owned by Pacific Gas and Electric Company (PG&E). The pilot flew solo from the right seat with the door removed, allowing him to lean out and observe. Examiners on the ground monitored the maneuvers.
According to the pilot, the first 20 minutes of the flight were normal. The accident occurred during the final phase while carrying a PG&E lineman on a 60-foot long line. The helicopter was maneuvering at about 175 feet above ground level (agl), positioning the lineman against a static line marker ball on a wire between a lattice tower and a wood pole. The pilot reported that the engine then lost power; he rolled the throttle out of the FLY detent into the emergency range, but the engine did not respond.
The pilot attempted to maneuver the lineman into a clearing and partially raised the collective when the lineman was about 15 feet agl to cushion the landing. He then maneuvered the helicopter away from the lineman and, after reaching about 30 feet agl, raised the collective and jettisoned the HEC line and cargo hooks. The helicopter landed hard. The engine remained running after landing, and the pilot shut off the main fuel valve and battery. He was extricated about 30 minutes later.
Multiple witnesses corroborated the pilot's account. They reported hearing a change in engine tone and observing the main rotor blades slowing as the helicopter descended rapidly. A video showed the helicopter descending just before impact; it appeared intact with no smoke or vapor.
Personnel Information
The pilot reported about 3,500 hours of total flight experience, including about 1,000 hours as a flight instructor and agricultural pilot. He began working for the operator about 15 months before the accident and had flown almost 175 hours in the Bell 407, including 10 hours in the Honeywell engine-equipped 407HP version, all in the accident helicopter.
The pilot had approximately 87 hours of total FAR Part 133 external load time before the accident. Most of this time was in the Eurocopter AS-350, with 2.3 hours in the Bell 407 and 6.7 hours in the 407HP. Two of those flights involved HEC; the remainder involved training or carriage of cargo or buckets, all flown from the right seat.
The accident flight was a demonstration for PG&E to qualify the pilot for HEC flights. According to the operator, this was the pilot's second check ride attempt after failing the first.
The pilot stayed in a hotel the night before, went to bed around 2100, awoke at 0630, and reported normal sleep and being well rested. He was 6 feet tall.
Aircraft Information
In 2019, the helicopter was converted from its original Rolls Royce 250-C47 engine to a Honeywell HTS900-2-1D engine under the Eagle Copters Eagle 407HP supplemental type certificate (STC) SR03496NY.
The Honeywell engine was controlled by a Full Authority Digital Engine Control (FADEC) system with two redundant electronic control units (ECUs), a fuel metering unit (FMU) assembly, a permanent magnet alternator, and various sensors. The FADEC system automatically controlled the engine during startup, steady state, and transient operations, ensuring operation within specified envelopes.
The pilot-commanded throttle position was monitored by the ECUs via a dual linear variable differential transformer (LVDT) assembly connected to a conventional twist grip on the collective control column.
The helicopter was configured for right-seat operation with the collective on the pilot's left. The twist grip had three distinct detent positions: OFF, IDLE, FLY, and an unmarked over-center position beyond FLY. In the Honeywell engine version, the over-center position had no functional use. In the original Rolls-Royce version, the over-center position (marked as MaxNG) allowed manual maintenance of rotor speed in case of FADEC failure.
To reduce engine power, rotating the twist grip from FLY to IDLE required clockwise rotation when facing forward. A lockout button was needed to move from IDLE to OFF.
Wreckage and Impact
The helicopter came to rest on its belly, tilted slightly left. The landing skids spread outward. The primary airframe structure was largely intact but buckled in the roof area below the main transmission, which had shifted and tilted down. All four main rotor blades remained attached; one was undamaged, while the other three had delamination, aft bending, and buckling from midspan outward. The tailboom remained attached; both tail rotor blades detached with roots remaining on the hub.
The engine remained on its mounts with minimal damage. The engine output drive coupling separated at the main transmission joint, consistent with transmission movement at impact. No evidence of catastrophic engine failure or foreign object ingestion was found.
The transmission drivetrain was continuous from the engine coupling through the main gearbox to the tail and main rotor blades; the freewheeling clutch was operational.
Flight controls sustained damage consistent with impact at the main transmission base and the pilot's collective control but were otherwise intact.
Flight Recorders
The helicopter was equipped with an Appareo Vision 1000 recorder capturing image, audio, and parametric data (GPS position, altitude, speed, 3-axis acceleration, pitch, roll, yaw). The unit was mounted on the left side of the aft cabin bulkhead, facing forward, with a field of view focused left and downward. Only a portion of the instrument panel, left annunciator panel, and external features through the left chin bubble and windscreen were visible. The pilot's body and control inputs were not captured.
The recording contained stereo audio: one channel from a cockpit area microphone, the other from the helicopter's intercom (a hot mic). Video playback had intermittent freezes, a known issue with the device, but audio was uninterrupted.
No annunciator lights on the visible left panel illuminated during the recording. Visible flight instruments included torque, measured gas temperature (MGT), Ng, oil pressure, oil temperature, transmission oil temperature and pressure, fuel capacity, amperes, and fuel pressure.
The video began at 0928:38 with the helicopter idling on the ground. After radio calls and gauge checks, the helicopter lifted off and maneuvered for the exam. The pilot was audible, breathing heavily, and at 0937:10 expressed frustration; gauges were normal. Radio communications with ground examiners continued.
At 0954:20, heading was 140° magnetic, MGT 710 °C, Ng 91%, torque 68%. Shortly after, the pilot exclaimed, torque dropped to 61% then returned to 65%. Heading changed left, and a steady 2,850 Hz tone (low rotor rpm horn or engine out horn) sounded for the remainder. MGT and Ng declined. The pilot made statements, heading swung right, and descent rate increased. The last frame showed the helicopter level with a power pole top about 4 seconds before impact.
Engine ECU data indicated the incident recorder activated when main rotor rpm reached zero. The first data point showed vertical speed zero, power lever angle (PLA) 102° (between IDLE and FLY), Nr 76.6% and decaying, Ng 87%. About 3.5 seconds later, PLA was 82° (IDLE), descent rate -500 fpm. Within one second, PLA increased to 142° (over-center past FLY), but Nr dropped to 50%, and engine parameters declined. Five seconds after over-center selection, engine parameters varied rapidly, and Np accelerated above 100% after Nr reached zero, consistent with decoupling at impact.
Honeywell representatives stated that when throttle is increased to FLY with Nr below 70%, a torque limiter engages to prevent over-torque, holding torque to 50% until 100% Np or 10 seconds elapse. This would prevent engine response to collective increase.
Tests and Research
The engine sustained minimal damage; the ECU was intact, but the FMU was damaged by impact from the rotating engine output drive coupling. The FMU was examined and tested; despite damage, it met nominal parameters, and disassembly revealed no preimpact anomalies or failures.
The engine was removed and tested at Honeywell Aerospace; no anomalies were noted, and it performed nominally in a test cell.
The throttle position LVDT was tested in a similarly equipped 407HP helicopter and performed within specifications.