What happened
On September 9, 2022, at approximately 15:40 UTC, a Cessna A188B agricultural aircraft, registration PT-WQN, was conducting aerial application operations near Santa Helena de Goiás, Brazil. After completing an application run, the pilot experienced engine performance oscillations. In an attempt to return to the landing area, the pilot repeatedly toggled the electric fuel pump and adjusted the mixture control. During this process, the engine suffered a complete failure, forcing the pilot to perform a forced landing in an unprepared, wooded field.
The investigation
The CENIPA investigation focused on the engine's performance and the integrity of the fuel system. Technical examinations of the Continental IO-520-ACD engine revealed that while the ignition system and spark plugs were functional, there was evidence of corrosion on the exhaust valve seats and valve tappets.
Crucially, investigators examined the aircraft's fuel system and discovered that the screen element of the right-side fuel tank filter had detached and was loose inside the tank. Furthermore, the header tank, which supplies fuel to the engine, contained significant amounts of debris and contaminants. The investigation also noted discrepancies in the aircraft's maintenance records, specifically regarding the traceability of certain accessories like the mechanical pump and magnetos, and identified that the pilot had performed unauthorized engine-driven fuel pump adjustments in the field with the operator's consent.
Findings
- The primary cause of the engine failure was fuel starvation resulting from debris and contaminants obstructing the flow of fuel through the header tank.
- The detachment of the right fuel tank's filter screen element allowed impurities to enter the fuel stream.
- The pilot's decision to switch the electric fuel pump on and off during the power loss was contrary to established supplementary procedures, which require the pump to remain ON during agricultural operations.
- The aircraft's maintenance documentation lacked proper traceability for several engine components.
- An inadequate organizational safety culture was indicated by the practice of allowing unauthorized field maintenance on the engine-driven fuel pump.