Cessna 205 N8495Z accident near Wagoner, Oklahoma

Probable cause

Maintenance personnel’s improper maintenance of the magnetos, which resulted in a loss of engine power.

NTSB analysis

During a post maintenance flight after the airplane's annual inspection, the pilot made about three circuits around the airport area before departing to continue flight maneuvers and performance checks. He started a left turn and then noticed a “very minor engine mis[fire]." As the pilot continued the turn, the "engine mis[fire]" began to increase and the engine began to shake. The airplane was unable to maintain altitude and was descending about 150-300 ft per minute. Although the pilot made multiple attempts to regain engine power, the engine lost total power. The airplane impacted trees and brush; during the landing sequence, the left and right wings buckled.

Following the accident, an engine run was performed; after running for 13 minutes, the engine lost power. Troubleshooting of the magnetos found that the right magneto was firing erratically. The right magneto was replaced with a known-good magneto and the engine was subsequently successfully test run at full power. More detailed testing of both magnetos revealed that they failed the manufacturer’s acceptance test procedures due to excessive point gaps and secondary coil resistance. A review of the engine logbooks revealed the magneto points and condensers were replaced about 18 years and about 230 flight hours before the accident flight. Given the available information, it is likely that maintenance personnel did not perform proper maintenance of the magnetos.

Text from the NTSB. Open the NTSB docket for ERA19LA006 for the full record.