What happened
On 5 July 2021, a Sling 2 aircraft, registered ZU-WCG, departed Mossel Bay Airport (FAMO) for Port Elizabeth Airport (FAPE) carrying a pilot and one passenger. During the flight over the Tsitsikamma region at 1500 feet, the pilot experienced engine roughness. In an attempt to stabilize the aircraft, the pilot climbed to 3000 feet and reduced power to continue the journey.
As the flight progressed, approximately 60 nautical miles from the destination, the occupants detected a burning odor, which appeared to originate from the electrical wiring. This was immediately followed by the illumination of both alternator warning lights on the instrument panel. Recognizing the developing electrical issue, the pilot elected to shut down the engine and utilized the aircraft's glide capability to reach Seaview Airfield (FAEW). The aircraft completed an uneventful landing with no injuries to the occupants and no damage to the airframe.
The investigation
Following the emergency landing, an aircraft maintenance engineer inspected the aircraft to identify the source of the electrical malfunction. The inspection revealed that the regulator for the "A" lane had failed. This primary failure triggered a secondary fault within the engine control unit, which subsequently caused damage to the "B" lane engine control unit.
To rectify the issue, technicians replaced the fuse box as well as both the "A" and "B" lane regulators. Subsequent ground testing confirmed that the engine performed within all normal parameters. Following these repairs, the aircraft was successfully flown back to Port Elizabeth.
Findings
- The initial engine instability was triggered by the failure of the "A" lane regulator.
- This component failure caused a cascading effect, leading to the damage of the engine control unit for the "B" lane.
- The presence of a burning smell indicated active electrical distress within the wiring/components prior to the total loss of alternator function.