Cessna 152 N49158 incident near Pilot Point, Texas

Probable cause

The loss of engine power due to the separation of the distributor gear arm on the left magneto.

NTSB analysis

The flight instructor and student pilot were conducting a training flight. After the student completed some maneuvers, the engine started running roughly. The flight instructor made several attempts to correct the problem without success. The airplane was unable to maintain altitude, so the flight instructor performed a forced landing to a field, which resulted in minor damage to the airplane.

An examination of the engine revealed that the Nos. 2 and 4 lower sparkplugs were lead-fouled and inoperative and that the Nos. 1 and 3 lower sparkplugs were lead-fouled but still operational. Further examination revealed that the distributor gear arm on the left magneto had separated and that the distributor gear arm on the right magneto was loose. Following the incident, the operator examined its fleet and found an additional 19 magnetos with loose distributor gear arms. The magneto manufacturer reported that it had seen 16 magnetos that exhibited similar failures. The manufacturer subsequently issued a service bulletin recommending that distributor gear assemblies in the affected magneto, which included the incident magneto, be removed and replaced at the "earliest convenient maintenance time, not to exceed the next 50 hours" with a replacement gear assembly.

Text from the NTSB. Open the NTSB docket for CEN15IA230 for the full record.