Mooney M20J N50BJ accident near Furnace Creek, California

Probable cause

The magneto clamps were not securely fastened to the mount, which led to a partial loss of engine power and a subsequent forced landing on unsuitable terrain.

NTSB analysis

A witness reported observing the airplane take off to the south and stated that the ground operations and takeoff appeared to be normal. The wreckage was located 2 days later on a flat, dry salt lake bed 7 miles south of the departure airport. The surface of the ground was deep jagged salt deposits, with crevasses between 6 and 18 inches deep, and unsuitable for making a successful off-field landing.

During the postaccident engine examination, the single-drive dual magneto was found mounted on the accessory pad and could be easily rotated by hand. The magneto had sustained no apparent impact damage and remained in good condition externally. Further examination of the attachment hardware found all required mounting studs, lock washers, and respective nuts to be in place and undamaged. The magneto clamps, respective magneto flange, and the accessory case interface areas exhibited wear signatures consistent with fretting, which suggested that the clamps were not securely fastened. These signatures were most prominent on the lower clamps and flange area. The magneto flange remained intact and revealed no evidence of cracking. It is likely that this could have produced a partial power loss, which led to the pilot’s decision to make an off-airport landing. No other mechanical failures or malfunctions were found that would have precluded normal operation. The airplane had accumulated about 10 hours since the last annual inspection. No maintenance records were located to determine if further maintenance had been performed on the engine since the inspection 5 months prior to the accident.

Text from the NTSB. Open the NTSB docket for WPR11FA114 for the full record.