What happened
On January 28, 2011, a Cessna 150M, registration PP-FOX, was conducting a flight instruction mission near Campo Grande, Mato Grosso do Sul. The flight was part of a training session involving simulated engine failure maneuvers.
At approximately 20:50 UTC, while the crew was performing a go-around at 1,0 and 000 feet AGL to simulate a second engine failure, the engine began experiencing intense vibrations and a significant drop in RPM. The instructor attempted to restore power by advancing the throttle to its limit, but the engine failed to respond.
Following established emergency procedures, the instructor shut down the engine and identified a suitable landing site in an unprepared pasture at Fazenda Sulam. During the landing roll, the aircraft encountered uneven terrain and had to swerve to avoid a concrete water trough. This maneuver caused the pilot to lose directional control, leading the aircraft to strike a wire fence. The impact resulted in severe damage to the right wing, engine, propeller, cowling, fuselage, and landing gear. Both the instructor and the student were uninjured.
The investigation
CENIPA investigators examined the engine, a Teledyne Continental Motors O-200-A, and reviewed the aircraft's maintenance records. The investigation focused on the mechanical cause of the power loss and the adequacy of the maintenance oversight.
Technical analysis of the engine revealed that the exhaust valve guide and the exhaust valve stem of cylinder number 4 were both outside the manufacturer's allowable tolerances. Furthermore, investigators found evidence of significant carbonization within the engine and corrosion at the bottom of the cylinder barrel. The investigation also scrutinized the aircraft's logbooks, noting discrepancies in how flight hours were recorded and inconsistencies in maintenance interval documentation.
Findings
- The stuck exhaust valve in cylinder number 4, caused by components being out of manufacturing limits, was the primary cause of the engine failure.
- Inadequate maintenance processes, including the failure to reset the Time Since New (TSN) after an engine rebuild and the performance of unprescribed 200-hour inspections, contributed to the occurrence.
- Deficiencies in maintenance supervision allowed improper documentation and non-compliant service labels to persist, which may have prevented the detection of the engine's deteriorating condition.
Safety action
CENIPA issued several safety recommendations to the Brazilian Civil Aviation Agency (ANAC), including:
- Directing oversight of the flight school to ensure proper completion of aircraft logbooks.
- Improving maintenance supervision methods to ensure compliance with manufacturer-prescribed programs.
- Auditing maintenance facilities to ensure their procedures align with the requirements of manufacturers like Teledyne Continental Motors.
- Enhancing inspection procedures for imported aircraft to ensure the traceability and reliability of maintenance records.