What happened
On August 27, 2016, a Cessna 172L, registration PT-DTW, was performing a flight training mission at Aeródromo Professor Urbano Ernesto Stumpf (SBSJ) in São José dos Campos, Brazil. The aircraft was operated by Aeroclube de São José dos Campos for private instruction purposes.
During the fourth approach to the runway, the pilot noticed the aircraft losing altitude. Upon attempting to increase power, the engine began running irregularly with low RPM. The pilot performed an emergency landing on the grass adjacent to runway 15. During the landing, the aircraft struck the ground with high energy, causing the nose gear to collapse. Following the impact, a fire broke out in the engine compartment, which ultimately destroyed the aircraft. The pilot sustained minor injuries and managed to evacuate the aircraft.
The investigation
CENIPA investigators examined the engine and the pilot's operational history. While the engine's mechanical components showed no inherent defects, investigators found black soot inside the combustion chambers, cylinders, and spark plugs, indicating an excessively rich air-fuel mixture.
The investigation focused on the meteorological conditions, which were conducive to carburetor icing (temperature of 18°C and dew point of 12°C). Investigators also reviewed the flight school's checklists, finding that the club used a condensed checklist that differed from the manufacturer's Pilot Operating Handbook (POH). Specifically, the condensed checklist modified the requirement for carburetor heat application, stating it should be used "as required" rather than mandating full heat before reducing throttle.
Findings
- The pilot had a valid license but possessed limited experience with the specific Cessna 172L model, having flown primarily in PA-28 aircraft.
- The engine failure was likely caused by carburetor icing, which was not prevented because the pilot did not apply carburetor heat as prescribed by the POH.
- The pilot's attempt to recover power by abruptly advancing the throttle likely caused the engine to flood, as the acceleration pump injected extra fuel that could not be properly atomized due to the ice restriction.
- The use of a condensed checklist by the operator contributed to a reduction in situational awareness regarding critical engine procedures.
- The emergency landing was performed with flaps retracted, resulting in a higher touchdown speed and increased impact energy.