What happened
On December 12, 2020, at approximately 18:00 UTC, a Neiva EMB-202 performing agricultural spraying operations in Rio Brilhante, Mato Grosso do Sul, experienced a critical engine failure. The aircraft, registration PT-UON, was operating over a plantation at Fazenda Alegrete when the pilot reported an abnormal noise followed by a sudden loss of engine power.
Faced with the loss of power, the pilot executed an emergency landing in an unprepared field. The impact resulted in substantial damage to the aircraft. The pilot, who was the sole occupant of the aircraft, escaped the wreckage uninjured.
The investigation
CENIPA investigators examined the wreckage and the Lycoming IO 540-K1J5 engine. Analysis of the propeller blades showed plastic deformation, indicating the engine was still rotating upon ground contact, though likely at low power. Evidence of fire was found around the engine cowling, specifically linked to the area where the cylinder had detached.
Technical examination of the engine components revealed that the fuel, lubrication, and ignition systems were all functional. However, investigators discovered that the third cylinder had completely detached from the engine block during flight. Detailed metallurgical analysis of the hardware used to secure the cylinder—specifically two through-studs and six bolts—revealed significant material fatigue. The examination identified "beach marks" on the threads of these components, which are characteristic of progressive fatigue failure.
Findings
- The primary cause of the engine failure was the progressive fatigue of the bolts and through-studs responsible for securing cylinder number three to the engine block.
- The failure of these fasteners led to the detachment of the cylinder, causing an immediate loss of compression and engine power.
- The investigation noted that improper torque application or failure to follow specific manufacturer tightening sequences and retorque procedures can induce localized stresses that accelerate fatigue.
- The pilot was fully qualified, with valid medical certification and appropriate agricultural flight ratings.
- The aircraft was within weight and balance limits and had a valid airworthiness certificate.
Safety action
It is recommended that the National Civil Aviation Agency (ANAC) disseminate the findings of this investigation to all maintenance organizations certified for the EMB-202 model. This is intended to reinforce strict adherence to manufacturer-specified maintenance practices, particularly regarding torque limits and the execution of retorque procedures, to prevent localized overloads and structural failures.