Incident Overview
On 1 January 2018 at approximately 1410Z, a Piper PA31-310 aircraft registered as ZS-MNS was operating a domestic charter flight under Part 135 from Pafuri Camp in Kruger National Park to OR Tambo International Airport (FAOR). The flight, which departed at 1205Z, carried two pilots and three passengers.
Flight History
En route, the flight encountered some turbulence. Air Traffic Control (ATC) cleared the aircraft to enter the FAOR Control Traffic Region at 7000 feet on a magnetic heading of 245°, with plans for a left base approach to Runway 21 Left. While at approximately 9 nautical miles inbound on Radial 070 from the JSV VOR, smoke began to enter the cockpit. The flight crew, uncertain of the source, noted the smoke had an electrical smell.
Crew Actions
The pilot flying declared a PAN PAN urgency call to ATC and opened the storm window to ventilate the cockpit. The pilot also switched off the electrical power as a precaution. ATC cleared the flight for a visual approach due to prevailing visual meteorological conditions. The aircraft landed safely on Runway 21 Left at 1415Z. Aerodrome Rescue and Fire Fighting Services escorted the aircraft to gate V2.
Post-Inspection Findings
No injuries were reported among the crew or passengers. Inspection revealed that the battery box top lid had burnt. The investigation found that the turbulence experienced during the flight caused the battery to shift within its compartment due to a poorly secured housing. The battery terminals made contact with the metal box lid, resulting in severe arcing that produced the smoke.
Maintenance Observations
Additional findings included burnt wires behind the circuit breaker panel and inside the nose area on the landing gear power pack system. Circuit breakers were found to be old and corroded. The battery box lacked a proper securing bracket to prevent such contact.