MIA02LA017 · Piper PA-24-250

The pilot stated that on November 16, 2001, he prepared to depart from his home airport, McCollum Field. As he performed an engine runup, he found the left magneto was not operating. He returned to the ramp and his mechanic disconnected and then reconnected the magneto "P" leads. The left magneto began to work. He departed McCollum Field and went to Peachtree City. He then flew to Tara Field, at Hampton, Georgia. When leaving Tara Field, he found that the left magneto was again inoperative. He called his mechanic and was told to disconnect the "P" leads and fly home. With the "P" leads disconnected, he could not check the magnetos. During takeoff, the engine appeared to develop full power. The EGT was normal. About 5 minutes after departure, the EGT pegged out high and one of the magnetos appeared to have quit. About a minute later, the engine quit. Atlanta Approach gave him radar vectors to the closest airport, Peachtree City. He could not make it to the airport and landed in a field with the gear down and full wing flaps extended. During rollout in the field, the airplane collided with a drainage ditch. The landing gear collapsed and the airplane slid to a stop. The magnetos had been overhauled by a local mechanic about 100 flight hours before the accident. During examination prior to running the engine after the accident, the "P" lead was disconnected from the right magneto and the spark retard lead was disconnected from the left magneto. The leads were reconnected and the engine was started. Only the right magneto was operating. The engine was operated to 1,500 RPM with a club propeller in the feathered position. The was no evidence of mechanical failure or malfunction of the engine assembly.The magnetos were tested at the manufacturers facilities. The left magneto condenser was inoperative causing the magneto to not operate. The right magneto operated normally. Manufacturer personnel stated that with one magneto inoperative, the exhaust gas temperature will become elevated due inefficient burning in the cylinder which carries over into the exhaust area. When you remove the "P" lead on these magnetos, they actually ground internally and become inoperative. Sometimes contamination prevents them from grounding immediately when the "P" lead is removed, but they eventually ground and become inoperative. He believes that with the spark retard disconnected on the left magneto and the "P" lead disconnected on the right magneto, that the left and right magnetos operated for takeoff due to the condenser working at this time on the left magneto and that the "P" lead internal grounding had contamination that prevented it from grounding immediately after removal of the "P" lead. Takeoff was normal at full power due to both magnetos working. Then either the left magneto quit due the condenser failing or the right quit due to it becoming internally grounded. The exhaust gas temperature went high and a small loss of power could be noted. Then the second magneto quit resulting in failure of the engine.

Verbatim NTSB analysis and probable cause from the NTSB dataset