What happened
On May 14, 2005, a Cessna 172 RG, registration EC-HYT, was conducting a local instructional flight with an instructor, a student, and one passenger. The flight originated from Cuatro Vientos Airport. During the flight, the crew noticed a significant imbalance in fuel consumption between the left and right wing tanks. To rectify this, they decided to land at a nearby ultralight airstrip in Sigüenza (Guadalajara) to transfer fuel.
Following the fuel transfer, the crew attempted a takeoff from the approximately 400-meter paved runway. The runway was situated at an elevation of 1,070 meters and featured a noticeable downward slope. During the takeoff roll, once the aircraft reached a speed of approximately 40 knots, the instructor noticed the nose began to descend toward the runway. The pilot believed the nose gear had retracted. The aircraft subsequently veered toward the right edge of the runway and came to a stop. The propeller struck the runway surface, resulting in deformation. There were no fatalities and no serious injuries among the three occupants, who evacuated the aircraft on their own.
The investigation
Investigators examined the aircraft's fuel system and landing gear mechanisms. Functional tests performed with maintenance support showed that the nose gear mechanism was operating correctly, as the gear could be retracted and extended through multiple cycles without issue. The fuel system also showed no signs of malfunction during testing, and fuel levels in both tanks were found to be equal after the incident.
Regarding the fuel imbalance noted earlier in the flight, the investigation focused on the wing tank ventilation. The investigators found that the abnormal consumption in the left tank could have been caused by excessive ventilation or increased suction in that tank, likely due to improper assembly or displacement of the ventilation pipe at the wing-to-fuselage junction.
Findings
- The primary cause of the runway excursion was the unintentional movement of the landing gear lever during the takeoff roll.
- The aircraft was operating on a short runway (400m) at a high elevation (1,070m), which left very little margin for error during the takeoff phase.
- The observed fuel imbalance was likely caused by improper mounting of the wing tank ventilation piping, leading to increased fuel suction in the left tank.
- The nose gear mechanism itself was found to be in good working order, and the landing gear lights indicated a transition state (amber) when the master switch was engaged during post-accident testing, supporting the theory of accidental lever movement.