What happened
On August 4, 2008, an EMB-201A aircraft, registration PT-GXV, was performing agricultural spraying operations at Fazenda Quebra Carro in Boca da Mata, Alagoas. During a spray pass, the pilot experienced a sudden loss of engine power and observed fire developing on the left side of the engine.
The pilot immediately executed an emergency landing into a nearby sugarcane field. During the impact, the left landing gear strut broke, causing the engine and propeller to strike the ground. The pilot escaped the aircraft without injury, but the aircraft sustained severe damage to the engine and landing gear, along with minor damage to the propeller blade and right wing tip.
The investigation
CENIPA investigators examined the engine components, specifically focusing on the cylinder #4 of the Lycoming IO540K1J5D engine. The investigation revealed that the failure was caused by the collapse of the bolts securing the cylinder. Specifically, two through-bolts and six studs holding cylinder #4 failed.
Technical analysis by the DCTA (Department of Science and Technology of the Brazilian Air Force) using scanning electron microscopy and metallographic examination determined that the fractures in the through-bolts likely occurred due to fatigue, which was facilitated by corrosion pits. The investigation also noted that while a service instruction required non-destructive testing (NDT) via magnetic particle inspection for these through-bolts, this procedure was not performed during the most recent overhaul because the bolts had been replaced at that time.
Findings
- The primary cause of the engine failure was the structural collapse of the bolts securing cylinder #4, which caused the cylinder to displace from the engine block, resulting in a ruptured cylinder head and significant oil leakage.
- Fatigue fractures in the through-bolts were likely initiated by corrosion pits.
- There was a possibility that improper torque was applied to the cylinder bolts during the last engine overhaul.
- The investigation could not determine if the failure of the through-bolts or the studs occurred first, as the broken pieces of the studs were not recovered.