What happened
On 04 April 2017, a Piper PA 25-235, registration ZS-MAD, was conducting agricultural spraying operations near Citrusdal Aerodrome. After approximately 90 minutes of spraying modified moths at Agterland Farm, the pilot began the return flight to the aerodrome. During this transit, the pilot noted unusual engine sounds accompanied by a burning odor and a rising oil temperature.
Shortly after these symptoms appeared, the engine ceased operation. The pilot identified a sandy field as a suitable site for an emergency landing. While the initial touchdown was successful, the aircraft struck a small bush during the landing roll, which caused the right main landing gear to collapse. Following the impact, a fire ignited within the engine compartment. The pilot managed to suppress the flames using a fire extinguisher and sand, though the fire caused significant damage to the engine's carburetor, oil filter, and magnetos.
The investigation
An investigation into the incident focused on the mechanical failure that led to the loss of power. Maintenance inspections conducted by the aircraft maintenance organisation (AMO) revealed that the engine had been backfiring across various power settings. The inspection identified a hole in the exhaust muffler, which allowed high-temperature gases to escape.
Findings
- The engine failure was triggered by hot gases escaping from a hole in the exhaust muffler.
- These escaping gases directly damaged the magnetos and their associated wiring.
- The failure of the magnetos and the burning of various hoses resulted in the total loss of engine power.
- The collapse of the right main landing gear was caused by the impact with vegetation during the forced landing.