What happened
On August 13, 2015, at approximately 12:50 UTC, a Chincul Sacaifi PA-25-260, registration PT-OQW, was performing agricultural spraying operations near Itariri, São Paulo. The aircraft had departed from a landing strip at Fazenda São Francisco to spray a banana plantation.
After completing the first spray pass, the pilot attempted a reversal turn for the second pass when the engine began to lose power. Realizing that controlled flight was no longer possible, the pilot executed a forced landing at a farm in the Ana Dias neighborhood. The aircraft sustained substantial damage to the landing gear, fuselage, and right wing, though the pilot emerged uninjured.
The investigation
CENIPA investigators, alongside specialists from the Department of Aerospace Science and Technology (DCTA), examined the Lycoming O-540-G1A5 engine. The investigation focused on the fuel system, where a thick layer of white powder was discovered inside the fuel filter and on various engine components.
Spectrometric analysis identified this substance as lead, a component of Avgas 100. The investigation established that the lead had precipitated and deposited on the fuel filter screen and blocked the filter's bypass valve, significantly restricting fuel flow to the engine.
To understand the cause of the precipitation, researchers conducted an experiment demonstrating that exposure to sunlight can cause lead to precipitate in Avgas 100 after several hours. The investigation noted that if the fuel used in PT-OQW had been stored or transported in translucent or transparent containers, it could have been exposed to sunlight, leading to the contamination found.