What happened
On August 24, 2018, a Cessna 150M, registration PT-WGV, was conducting a navigation training flight from Ubatuba to São José dos Campos. The flight plan included a touch-and-go maneuver at Guaratinguetá. While climbing through approximately 5,500 feet, the crew experienced a drop in engine RPM.
In an attempt to mitigate the issue, the crew activated the carburetor heat system. However, a subsequent drop in RPM occurred shortly after. Faced with continued power loss, the pilots elected to shut down the engine and perform a forced landing in a rural area near Cunha, São Paulo. The impact resulted in substantial damage to the aircraft. The flight instructor sustained serious injuries, while the student sustained minor injuries.
The investigation
CENIPA investigators examined the aircraft's maintenance history and the engine's performance. The aircraft had undergone a 50-hour inspection only three days prior to the accident, and all documentation, including airworthiness certificates and pilot licenses, was valid.
Technical analysis of the Continental O-200-A(48) engine was conducted by the Institute of Aeronautics and Space (IAE). While functional tests of the engine revealed no mechanical anomalies or malfunctions, investigators noted significant water condensation on the exterior of the carburetor. Meteorological data from the day of the accident showed relative humidity levels between 50% and 70% at 5,000 feet, which is conducive to icing conditions.
Findings
- The engine model is susceptible to a sharp drop in air/fuel mixture temperature under specific atmospheric conditions.
- Carburetor icing is the suspected cause of the power loss, as the environmental humidity and observed condensation supported this hypothesis.
- The crew's application of carburetor heat may have been delayed or insufficient to prevent the engine failure.
- The aircraft was within weight and balance limits and maintained all required maintenance schedules.