What happened
On August 2, 2012, a Cessna 150L, registration PR-LTB, was conducting a flight training mission departing from the Aeródromo Nacional de Aviação in Goiânia, Brazil. The crew, consisting of a flight instructor and a student pilot, was performing maneuvers within the traffic pattern at approximately 1,000 feet when the engine experienced a sudden loss of power.
The pilots declared an emergency to Anápolis Approach (APP-AN) and executed an emergency landing on a public roadway in the Tropical Verde neighborhood of Goiânia. Following the touchdown, the aircraft struck a sandbank, causing the plane to capsize. Both occupants sustained minor injuries, while the aircraft suffered substantial damage to the engine, propeller, fuselage, wings, and landing gear.
The investigation
CENIPA investigators examined the engine components and maintenance records to determine the cause of the power loss. While the pilots were qualified and the aircraft's airworthiness certificate was valid, investigators identified significant discrepancies in the maintenance documentation. Although recent cylinder replacements and a carburetor change had reportedly occurred, these services were not properly recorded in the aircraft's logbooks.
Technical inspections of the engine revealed that a fuel line connection nipple, leading from the tanks to the filter, was improperly secured, held only by a single thread. Furthermore, engine testing showed critical compression failures: cylinders 1 and 4 exhibited zero compression, while cylinder 3 showed only 20 PSI. Upon disassembly, investigators found that the intake valve of cylinder 1 had seized in the open position within its guide.
Findings
- The primary cause of the engine failure was related to improper aircraft maintenance.
- The intake valve in cylinder 1 had seized in the open position, likely due to excessive heat transfer caused by inadequate valve seating.
- Cylinders 1, 3, and 4 exhibited critically low or zero compression due to a phenomenon known as "glazing" (espelhamento), where a varnish-like layer of oxidized oil covers the cylinder walls, preventing proper ring seating.
- A fuel line connection nipple was inadequately tightened, which could have caused a fuel leak and a lean air-fuel mixture.
- Maintenance records were incomplete, with several recent engine repairs and component replacements not documented in the aircraft's logbooks.