History of Flight
On 4 April 2017 at 0545Z, a Piper PA-25-235, registration ZS-MAD, departed from Citrusdal Aerodrome to spray modified moths on Agterland Farm, located approximately 4.4 nautical miles north of Citrusdal. The pilot, who held a valid Commercial Pilot License and had 2481.9 total flying hours with 235.8 hours on type, maintained an en-route altitude of 1000 feet above ground level. After 1.5 hours of spraying, while returning to Citrusdal, the pilot noticed the engine sounding differently, a smell of burning, and rising oil temperature. Within a few minutes, the engine stopped. The pilot selected an open sandy field for a forced landing.
Forced Landing and Post-Impact Fire
During the landing roll, the aircraft struck a short bush, which broke the right main landing gear. The aircraft came to a stop. A fire had already started in the engine bay and intensified after stopping. The pilot used a fire extinguisher and sand to extinguish the flames, which were confined to the engine bay. The fire damaged the carburettor, magnetos, and oil filter. One person (the pilot) was injured; no fatalities were reported.
Investigation Findings
The aircraft maintenance organization (AMO) that examined the aircraft found that the engine backfired at different power settings. A hole was discovered in the exhaust muffler. Hot gases escaping from this hole burned the magnetos and their wiring, leading to the engine failure. Subsequent damage to other hoses contributed to the failure sequence.
Probable Cause
Unsuccessful forced landing following an engine failure as result of damaged magnetos caused by damaged exhaust muffler.