What happened
On October 27, 2009, a Cessna 170 A, registration PT-AQO, was performing a training flight at the Sítio Pouso do Aviador aerodrome in Campo Grande, Brazil. The flight was intended to help the pilot prepare for the renewal of a technical rating. After completing a series of touch-and-go maneuvers, the aircraft was performing its second go-around at approximately 300 feet when the engine failed.
In an attempt to avoid obstacles following the power loss, the pilot executed a sharp right turn. This maneuver caused the right wing of the aircraft to strike a tree before the plane impacted the ground. The pilot escaped without injury, while the co-pilot sustained minor injuries. The aircraft suffered severe damage to the engine, propeller, landing gear, and right-side components, including the wing, flap, and aileron.
The investigation
CENIPA investigators examined the fuel system and found significant contamination. Analysis of the fuel in the fuel filter bowl revealed a white, paste-like substance consisting of dirt and water. Laboratory tests confirmed that the fuel was heavily contaminated with free water, making it unfit for aviation use.
Investigators also noted corrosion on the carburetor chamber and severe corrosion on the fuel tank floats. While the pilot had performed a fuel drain prior to takeoff, the investigation determined that water likely accumulated in parts of the fuel system not reached by the drain. The presence of corrosion suggested that water had been present in the system for an extended period. The investigation considered two primary sources for this moisture: condensation resulting from the aircraft being left with partially empty tanks for several days, or water entering the tanks through the filler neck during aircraft washing.
Findings
- Fuel contamination: The primary cause of the engine failure was the presence of water in the fuel system, which inhibited combustion.
- Flight indiscipline: The pilot was operating with an expired single-engine land rating, and the flight was being conducted as an unauthorized training session since the co-pilot was not a certified flight instructor.
- Maintenance observations: Although the aircraft's maintenance was up to date, the recent 100-hour inspection had not detected the existing corrosion in the carburetor or fuel tank floats.
- Operational factors: The accumulation of water was likely driven by condensation due to the aircraft being stored with low fuel levels or potential water ingress during cleaning procedures.