What happened
On April 20, 2018, a Bell 429 helicopter, registration PK-WSX, operated by PT Whitesky Aviation, was performing an unscheduled passenger charter flight near Morowali, Sulawesi Tengah. The flight was traveling from the IMIP helipad toward Kendari with one pilot, one engineer, and six passengers on board.
Shortly after takeoff, at an altitude of approximately 600 feet, the crew identified a failure in one of the Engine Control Units (ECU). The pilot decided to abort the mission and return to the IMIP helipad. During the attempt to return, the pilot transitioned one of the throttles to manual mode. As the pilot manipulated the controls, the aircraft's airspeed and altitude began to decline. Before the helicopter could reach the landing site, it struck a factory access road approximately 175 meters from the helipad. While all occupants of the aircraft survived the impact, a pedestrian walking on the road was fatally injured.
The investigation
The investigation examined the aircraft's flight data, cockpit voice recordings, and the mechanical state of the engines and transmission. Investigators found that while the Crew Alerting System (CAS) displayed an "ECU 1 FAIL" message, the engineer was unable to correctly identify the failing engine. This confusion was compounded by the pilot's manual manipulation of the throttles, which triggered additional "THROTTLE 1" and "THROTTLE 2" alerts.
Data from the Flight Data Recorder (FDR) revealed that the pilot mistakenly focused on managing the throttle for engine 2 instead of engine 1. Consequently, the pilot placed the engine 1 throttle in the FLY detent while simultaneously reducing the power on engine 2. Because the engine 1 fuel control system had reverted to manual mode, it could not meet the power demands required by the increasing collective pitch. Simultaneously, the reduction in engine 2 power prevented the aircraft from maintaining necessary energy.
Findings
- The primary cause of the crash was the loss of main rotor (NR) RPM to a level below 95%, which rendered the aircraft unable to maintain flight.
- The pilot made an inappropriate decision to manipulate the throttle for engine 2 rather than engine 1 following the initial failure.
- The engineer's inability to accurately identify the specific engine failure contributed to the pilot's incorrect corrective actions.
- A lack of specific simulator training regarding Electronic Engine Control (EEC) failures left the crew unprepared for the technical complexities of the malfunction.
Safety action
Following the accident, PT Whitesky Aviation implemented several safety measures, including the establishment of a working group to review emergency procedures and the issuance of safety notices regarding single-pilot resource management. The KNKT has recommended that the operator review engineer training regarding system failure indications and ensure that pilot simulator training includes handling for specific system abnormalities like ECU failures.