What happened
On 21 November 2024, an Airbus AS350B3 helicopter, registration ZS-RWG, was conducting a surveillance mission for the Gauteng Traffic Police. The flight departed from the Ultimate Heli helipad in Midrand, heading toward Pretoria East for traffic monitoring.
During the return leg, while flying at approximately 400 feet above ground level near Eco-Park Estate, the pilot heard a loud noise followed by a sudden drop in engine torque and power. As the main rotor RPM plummeted, the pilot initiated an autorotation to perform a forced landing. The aircraft descended rapidly and struck a field in Brakfontein, near Midstream Estate, with its left front skid gear. The impact was severe enough to cause the tail boom to fold and the tail rotor drive shaft to decouple. The helicopter slid approximately 20 metres before coming to a halt. Despite the substantial damage to the airframe, there were no injuries to the pilot or the two passengers.
The investigation
SACAA AIID investigators examined the wreckage and the aircraft's maintenance history to determine why the engine failed. The investigation focused on the Electronic Engine Control Unit (EECU) and its power supply architecture. Investigators analyzed the electrical components and reviewed the service history of the aircraft to identify any missed maintenance requirements or known vulnerabilities in the engine's control systems.
Findings
- The primary cause of the engine flameout was the failure of capacitor C179 on the Lane A power-supply board. This failure interrupted the electrical supply to the stepper motor, which prevented the delivery of fuel to the engine.
- The failure occurred at a low altitude, which left the pilot with insufficient time to diagnose the electrical malfunction or utilize the manual fuel backup system.
- Non-compliance with a critical manufacturer service bulletin was a major contributing factor. The aircraft had not been updated according to Service Bulletin SB-C12380-49-009-01, which was designed to address vulnerabilities in the EECU power supply circuitry. This omission left the engine control system susceptible to the power loss that ultimately led to the flameout.