Cessna 182 N1311S accident near Cleveland, Tennessee

Probable cause

The undetected wear of the ignition switch and key, which allowed removal of the key from an intermediate position and subsequently led to an unintended engine start-up. Contributing to the undetected wear of the 42-year-old ignition switch was the lack of guidance by the switch manufacturer and airframe manufacturer for procedures to detect lack of integrity between the ignition key and switch.

NTSB analysis

After completing a personal flight with his wife, the private pilot secured the engine by placing the mixture control in the idle cut-off position. Based on physical evidence observed after the accident, he likely moved the ignition switch toward the off position and removed the key. The pilot's wife indicated that, after they performed local errands and returned to the airport, the pilot was performing his preflight inspection of the airplane with the ignition key in his pocket. Although airport security video did not capture the accident sequence and the pilot's wife, who was by the airplane's right cabin door, did not see her husband move the propeller, she heard the propeller move and the engine starting or trying to start. The pilot likely slightly moved the propeller and the engine briefly started; the propeller then rotated and fatally injured the pilot. The engine did not sustain operation, and the propeller ceased rotating.

Postaccident examination of the 42-year-old ignition switch revealed that it appeared to be in the off position when observed visually from the pilot's seat, but its actual selected position was more toward the right magneto position. The switch and key were determined to be slightly misaligned with the instrument panel placard markings. On- and off-airframe operational testing of the ignition switch in the as-found position revealed the right magneto was hot, or not grounded. In addition, examination of the cut surfaces of the key notches revealed relatively smooth and reflective surface features consistent with a worn surface on the flank of the notch adjacent to the key retention ridge and on the tip end of the shank opposite the notched side. Examination of the key cylinder revealed an area with a smooth and reflective surface consistent with wear on the lower side of the key slot. The location and shape of the worn area was consistent with wear contact with the tip of the key as it was inserted and removed. The key could be removed from the switch in any of the five positions due to the wear of the switch's internal components, contrary to its intended function that would retain the key in any position except the off position. Although the switch manufacturer tested all new switches to ensure this functionality when new, that test is not specified to be performed at any time as part of any inspection or checklist by the switch manufacturer, airframe manufacturer, or Title 14 Code of Federal Regulations Part 43 Appendix D.

Although the mechanic who performed the last annual inspection reported the key-to-switch integrity was satisfactory with no discrepancies, the worn condition of the ignition switch likely existed at the time of the annual inspection, which was about 31 flight hours before the accident flight (excluding the pilot's previous flight the day of the accident). Additionally, during the annual inspection when the mechanic installed the ignition switch after repairs, he failed to properly align the switch positions with the marks on the instrument panel placard.

Text from the NTSB. Open the NTSB docket for ERA18LA199 for the full record.