Accident Overview
A pilot was conducting touch-and-go landings and takeoffs. During the final takeoff, a ground witness reported that an engine began to backfire. The airplane started to descend while the backfiring continued, and it eventually disappeared from the witness's view.
Another pilot, also practicing touch-and-go landings and takeoffs, observed the airplane lying northeast of the departure end of the runway.
Engine Examination
An examination of both engines found no evidence of any internal preexisting malfunctions or failures. However, the timing of the right engine's magnetos exceeded the manufacturer's service limits. According to an accessory repair technician, neither magneto was considered airworthy.