What happened
On February 15, 2014, a Cessna 150L, registration PR-BRP, was conducting a flight instruction mission near Trindade, Goiás. The flight, operated by Aeroclube de Goiás, carried an instructor and a student pilot. Approximately 20 minutes after departing from the Goiânia National Aerodrome (SWNV), the crew was performing a simulated engine failure procedure. During the go-around phase of this simulation, the engine suffered an actual power loss.
The instructor took control to execute an emergency landing. While approaching a cornfield for the forced landing, the aircraft's nose gear struck a low-voltage power line. This impact caused the aircraft to nose-over (pilonamento), coming to rest on its back. Despite the substantial damage to the aircraft, both occupants emerged uninjured.
The investigation
CENIPA investigators examined the Continental O-200-A engine and found that the propeller had no significant deformation, indicating it was not producing traction at the time of impact. Post-accident inspections of the engine revealed that cylinder number 4 was inoperative during cold compression tests. However, after the engine was run at operating temperature, the cylinder functioned normally.
Detailed teardown of the engine identified a dimensional discrepancy between the intake valve stem and its guide in cylinder 4. The investigation determined that during the simulated failure, the engine remained at idle for an extended period. The external airflow caused the cylinder to cool and contract, while the internal temperature remained high, eliminating the clearance between the valve stem and the guide and causing the valve to seize. Additionally, investigators found that the oil pressure regulator spring was incorrect; a spring larger than the one specified in the manufacturer's manual had been installed, which explained the high oil pressure observed during cold starts.
Findings
- Improper maintenance of the aircraft's engine components.
- Inadequate management supervision regarding maintenance quality control.
- The installation of an incorrect oil pressure regulator spring.
- A dimensional mismatch between the intake valve stem and the guide in cylinder 4, exacerbated by thermal contraction during the idle phase of the simulation.