What happened
On February 17, 1996, at approximately 14:25, a Piper PA-12, registration PT-AMQ, was conducting a banner towing operation along the coast of Praia da Enseada, in Guarujá, São Paulo. Approximately 50 minutes into the flight, the engine experienced a sudden loss of power accompanied by intense vibration following a loud, sharp noise.
The pilot immediately released the towed banner and initiated emergency procedures for a forced landing. As a precaution, the pilot unlocked the aircraft door to facilitate egress. The aircraft touched down on the water with wings level and a slightly nose-down attitude, but subsequently capsized. The pilot, who was restrained only by a two-point harness, struck his head during the sudden deceleration, resulting in minor injuries. After the aircraft came to a stop, the pilot grabbed a life jacket, abandoned the aircraft, and swam to the shore, where he was rescued by bystanders.
The investigation
CENIPA investigators examined the engine, which was disassembled at a maintenance facility. The inspection revealed that a control valve in one of the cylinders had fractured. The valve was sent to the Institute of Aerospace Technology (IFI/CTA) for metallurgical analysis. However, due to extensive corrosion and physical deformation on the fracture surface, investigators could not definitively determine the exact mechanism that caused the failure.
While the investigation noted that similar failures have been reported in Lycoming engines—potentially due to fatigue—the lack of conclusive data regarding the specific cause of this fracture prevented a definitive ruling on manufacturing defects. Additionally, the investigation noted that the maintenance history regarding the specific service life of this valve was not sufficiently researched. The investigation also faced challenges in evaluating human factors due to the significant delay in conducting psychological interviews with the pilot.