Electrical failure leads to fatal crash

This October 2008 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

Aircraft: Cessna 206. Injuries: 2 Fatal. Location: Estacada, Ore. Aircraft damage: Destroyed.

What reportedly happened: The pilot was on a VFR night flight when he used his cellphone to call an airport employee asking that he turn on the runway lights because the airplane’s electrical system had failed. The employee stated the airplane flew over the airport at an altitude of approximately 800 feet above ground. The airplane was on a westerly heading with no lights on. As the airplane passed over the runway and initiated a left turn, the witness lost visual contact with the airplane, then heard the sound of impact. The wreckage was found in trees about 1,000 feet short of the runway’s approach end.

Detailed examination of the recovered wreckage revealed that the top ground terminal nut that attached the alternator filter to the ground terminal of the alternator was loose. There was evidence of severe wear on the alternator filter attach point and the bottom alternator ground terminal nut. Copper particle splatter was observed around the ground terminal and on the alternator filter which was found to be consistent with electrical arcing. The alternator controller remained attached to the firewall. The tamper-proof seal on the controller was found separated at the seam. The controller cover was removed and a diode was observed separated from the circuit board and found loose within the cover. There was evidence of heat damage within the lower inboard corner of the printed circuit board where the diode was installed.

Probable cause: The pilot’s failure to maintain clearance from trees while on approach to land at night. Contributing to the accident was the electrical system failure and the pilot’s diverted attention.

For more information: NTSB.gov