What happened
On August 9, 2021, a Tecnam P2002-JF, registration HB-KOP, was conducting a training flight at Grenchen Airport (LSZG). The flight, which began as a routine training mission from Yverdon, involved a flight instructor and a student pilot.
Shortly after departing from runway 24, the crew observed thick black smoke emanating from the lower right corner of the instrument panel. The flight instructor immediately took control of the aircraft, initiated a turn to runway 06, and notified the tower. The aircraft landed safely on runway 06 approximately three minutes after takeoff. The crew taxied the aircraft to the parking area, where the airport fire service met them. No injuries were reported, though the aircraft sustained light damage.
The investigation
An investigation by the Swiss Transportation Safety Investigation Board (SUST) focused on the electrical system of the aircraft. Post-incident maintenance inspections revealed that two 22,000 μF capacitors, which are wired in parallel to ensure the proper operation of the rectifier regulator, had burst. The failure of these components also caused the 50-A fuse for the regulator to blow. These specific capacitors had been in service for approximately 500 flight hours since their installation in March 2019.
Findings
- The primary cause of the smoke was the bursting of two capacitors located on the cabin side of the firewall.
- The failure of one capacitor in this parallel configuration typically places excessive stress on the remaining capacitor, leading to its subsequent failure.
- The investigation highlighted a persistent safety deficiency regarding these components in Rotax-powered aircraft. Similar incidents involving the same type of failure occurred in 2013 and 2017.
- While the manufacturer introduced a life limit of 4 years or 1,000 flight hours for these capacitors in 2015, the investigation noted that the underlying safety issue remains unaddressed by regulatory authorities.