What happened
On May 1, 2010, a Cessna 172F, registration PT-CHQ, was performing a ferry flight from Almenara, MG, to Ilhéus, BA. The flight followed a maintenance service performed the previous day. During the flight, the engine began to exhibit significant RPM fluctuations, which eventually led to a complete engine failure at approximately 1,300 feet altitude.
Recognizing the emergency, the pilot identified a nearby pasture at Fazenda Aliança, BA, as a suitable landing site. Before touchdown, the pilot closed the fuel valve to mitigate fire risk and deployed the flaps. The aircraft performed an emergency landing in the pasture, skidding approximately 20 meters before striking a wire fence. The impact caused light damage to the engine cowling, wing struts, and landing gear. The pilot and one passenger were uninjured.
The investigation
CENIPA investigators examined the aircraft' and found several critical maintenance discrepancies. During the inspection of the left fuel tank, investigators discovered that the fuel tank vent was positioned approximately 4 inches below the lower surface of the wing, rather than the 4.62 inches required by the maintenance manual. This displacement, caused by the absence of a rubber protection on the clamp, prevented proper dynamic pressure equalization, thereby interrupting the fuel flow to the engine.
Furthermore, the investigation revealed that the engine carburetor was overdue for its required overhaul and contained multiple irregularities, including an uncalibrated float, an incorrect throttle shaft, and an improper diffuser. The investigation also identified several expired inspection intervals for various aircraft components, such as the engine air filter and seat restraint assemblies.
Findings
- Inadequate maintenance of the fuel system and carburetor was the primary cause of the engine failure.
- The displacement of the fuel tank vent prevented the necessary pressure equalization for continuous fuel flow.
- There was a lack of adequate maintenance supervision, which allowed various overdue inspections and unapplied Airworthiness Directives (ADs) to persist.
- The carburetor was operating with several non-compliant parts and overdue service intervals.