Incident
On 16 May 2017 at 10:43 local time, a Cessna 172 (registration HB-CGI) operated by Alp-Air Bern AG was on a private visual flight rules (VFR) flight from Bern-Belp Airport (LSZB) to the same airport. During the cruise phase, the pilot noticed smoke emanating from the cockpit, indicating an electrical short-circuit. The pilot immediately cut the aircraft's master electrical switch, which reduced the smoke emission. Without reactivating the electrical system, he executed a precautionary landing at Ecuvillens Airfield (LSGE).
The pilot, a Swiss citizen born in 1943, held a private pilot license (PPL(A)) issued by the European Aviation Safety Agency (EASA) and the Swiss Federal Office of Civil Aviation (FOCA). He had accumulated 788 total flight hours, including 600 hours on the Cessna 172 type and 4 hours in the preceding 90 days.
Aircraft Damage and Injuries
The aircraft sustained slight damage to its electrical wiring and avionics. No other damage was reported. The pilot was not injured; no passengers or other persons were on board.
Investigation
The post-incident examination revealed that a short-circuit or overheating of an electronic component had occurred in the left fuel tank gauge. This caused the smoke emission. The investigation concluded that a single defective component was responsible for the short-circuit and smoke, and no systemic cause was found.
Conclusions
The Swiss Transportation Safety Investigation Board (STSB) noted that the pilot's immediate action to cut the master switch was prudent, as he could not determine which electrical elements were causing the smoke. Since the electrical system is not essential for safely guiding the aircraft under VFR, it was reasonable not to reactivate it. The decision to discontinue the flight and land at the nearest suitable airfield was taken for safety reasons.
Based on the finding of a single defective component and no systemic cause, the STSB closed the investigation with a summary report on 3 October 2017, in accordance with article 45, paragraph 1 of the Ordinance on Safety Investigations of Transport Incidents (OEIT).