Primary finding
Probable cause
A partial loss of engine power due to the pilot’s improper installation of the engine’s No. 1 cylinder spark plugs.
Investigator assessment
Analysis narrative
According to the pilot, during the turn from the base leg to final approach, the engine experienced a partial loss of power. He performed a forced landing into some small trees because he knew he could not glide the airplane to the runway. The airplane sustained substantial damage to the wing spars. A postaccident examination revealed that a spark plug was backed out of the No. 1 cylinder and was suspended from the electrode wire. The pilot reported that he had changed the engine spark plugs the day before the accident and that he may have cross-threaded one of them.
Source record
Factual narrative
According to the pilot during the turn from the base leg to the final approach the engine experienced a partial loss of power. The airplane impacted a tree causing substantial damage to the wing spars. A Federal Aviation Administration inspector examined the wreckage and noted that one spark plug was found backed out of the No. 1 cylinder and was suspended from the electrode wire. The pilot reported that he had changed the engine spark plugs the day before the accident and that he may have cross-threaded one of the spark plugs.