What happened
On 1 January 2018, a Piper Aircraft Corporation PA31-310, registration ZS-MNS, was operating a commercial charter flight from Pafuri Camp in the Kruger National Park toward OR Tambo International Airport. The flight, carrying two crew members and three passengers, encountered turbulence during the en-route phase of the journey.
While positioned approximately 9 nautical miles inbound on the JSV radial, the flight crew noticed smoke entering the cockpit. The crew identified the odor as being of an electrical nature. In response, the pilot flying declared a PAN PAN urgency signal to Air Traffic Control and deactivated the aircraft's electrical power. The pilot also opened the storm window to mitigate the smoke levels. The aircraft was subsequently cleared for a visual approach and landed safely at OR Tambo International Airport with no injuries to the occupants.
The investigation
The SACAA AIID investigation focused on the source of the smoke and the physical condition of the aircraft's electrical systems. Post-flight inspections of ZS-MNS revealed that the top lid of the battery box had been burnt. Investigators located burnt wiring behind the circuit breaker panel and within the nose area near the landing gear power pack system. Additionally, the circuit breakers within the panel were found to be aged and showing signs of corrosion.
Findings
Technical analysis established that the primary cause of the smoke was severe electrical arcing within the battery bay compartment. This arcing was triggered when the battery terminals made physical contact with the metal lid of the battery box. The investigation determined that the battery was not sufficiently restrained; due to a lack of a proper securing bracket, the battery was able to shift within its housing when the aircraft encountered turbulence. This movement allowed the terminals to strike the metal lid, initiating the electrical fault.