What happened
On August 22, 2014, a private Piper Arrow (HB-CDE) was conducting instrument landing system (ILS) approach training near Lahr, Germany. The flight was being operated under visual flight rules (VFR) with a safety pilot on board to supervise the training.
During the second approach, as the aircraft intercepted the localizer at approximately 4,000 feet, the crew observed yellow smoke emerging from beneath the instrument panel. This was accompanied by the smell of burning plastic. Shortly after the smoke appeared, the primary flight data display indicated that the aircraft's electrical supply had switched to the onboard battery, and the avionics system subsequently failed.
In response to the emergency, the crew initiated a descent toward the airport, closed the firewall ventilation inlets, and opened the cockpit windows. After following emergency checklists and turning off the main avionics switch, the crew attempted to declare a 'Mayday' via a portable radio, though the tower did not initially understand the transmission. Despite the loss of primary avionics, other flight instruments remained functional. The crew decided to proceed with the landing, deploying the landing gear according to emergency procedures but opting not to extend the flaps. The aircraft landed safely on runway 21.
The investigation
Investigators examined the aircraft to determine the origin of the smoke and the cause of the electrical failure. The inspection focused on the area beneath the instrument panel where the smoke was first observed.
Findings
- The investigation established that the faulty seal of a cigarette lighter was the primary cause of the incident.
- This lighter was connected directly to the primary electrical bus without an integrated circuit breaker.
- The damaged seal allowed for a condition that caused the insulation of adjacent wiring to chafe, resulting in a short circuit.