2004 Cessna 172N Incident at Finca del Alamín (EC-HAT)

Incident Overview and Flight Details On September 2, 2004, at 11:45 local time, a Cessna 172N with registration EC-HAT, operated by American Flyers España, departed from Cuatro Vientos Airport for a local training flight. The aircraft was equipped with a single Lycoming O-320-H2AD engine. The flight was conducted under dual command, with a student pilot and an instructor on board. ## Sequence of Events During the flight, the crew performed a series of maneuvers and a simulated engine failure south of Villadelprado, Madrid. The instructor reported that the aircraft initially recovered correctly, gaining speed and altitude at 2,500 rpm. However, at 600 feet above the ground, with 10 degrees of flaps retracted, the engine experienced a power drop to 2,000 rpm, followed by severe vibration. Attempts to resolve the issue by cutting and reapplying power, as well as adjusting the mixture, were unsuccessful. Unable to maintain altitude, the pilot decided to make an emergency landing. ## Emergency Landing and Aftermath The pilot identified a suitable field and selected the appropriate flap setting for the landing. The aircraft touched down safely, and both occupants confirmed there were no personal injuries or material damage to the aircraft. The aircraft was later transported to a hangar for a detailed engine inspection. ## Engine Inspection Findings Prior to inspection, 125 liters of fuel were removed from the aircraft. The inspection revealed that the pushrod and its protective sleeve for the exhaust valve of cylinder number 2 were bent. The pushrod was made of aluminum with steel ends. Significant wear marks were found on the valve stem, and carbon residue was present at the bottom of the cylinder. A distinct circular mark was visible on the piston. ## Analysis and Conclusions Analysis of the engine components indicated that the circular mark on the piston was caused by the exhaust valve. The valve had become stuck in a specific position, as evidenced by the wear mark on its stem. The investigation concluded that the presence of dirt and inadequate lubrication likely caused the valve to seize due to welding in a high-temperature area. The valve remained open, which reduced the internal pressure in the cylinder during the compression phase, resulting in ineffective combustion. This condition explained the engine's inability to provide sufficient power to gain altitude and the vibrations reported by the pilot.