What happened
On October 8, 2003, a Cessna 177-RG, registration EC-HZI, was conducting a flight competency check for an instrument rating revalidation near Málaga Airport. The flight involved local maneuvers, including instrument departures, holding patterns at the MGA VOR, and various instrument approaches.
During the flight, the crew experienced significant electrical anomalies. While holding at the VOR, they noted loud noises through the speakers, the failure of all audio and navigation screens, and erratic needle oscillations on non-engine-related instruments, such as the alternator and fuel gauges. These fluctuations occurred in cyclic 10-second intervals. Due to the loss of communication, the pilot declared a radio failure using transponder code 7600 and proceeded toward the coast to return to Málaga.
Upon approaching the airport, the crew re-engaged the master switch, alternator, and avionics. Although communications were initially difficult, they eventually established contact with the tower and received landing clearance. During the landing roll, the pilot maintained a nose-high attitude and decelerated without using brakes. When the aircraft speed dropped to approximately 10 knots, the main landing gear legs began to retract. This caused the tail to impact the runway pavement, resulting in damage to the right side of the horizontal stabilizer, the right wingtip, and the ADF antenna.
The investigation
Investigators examined the aircraft's electrical system and the sequence of events leading to the gear retraction. The investigation revealed that the aircraft had required an external power source to start the engine because the battery was nearly discharged.
Post-accident inspections showed that while the landing gear could be extended and locked manually, the electrical system experienced intermittent power interruptions. The investigation focused on the alternator's overvoltage protection sensor and the crew's decision-making regarding the landing gear configuration.
Findings
- The primary cause of the electrical failures was intermittent power interruptions caused by the alternator's overvoltage protection sensor, likely due to a malfunction in the sensor itself.
- The electrical load from re-engaging all systems, combined with the battery's low state of charge, likely triggered the overvoltage sensor to disconnect the alternator.
- The landing gear failed to fully extend because the electrical interruption occurred during the extension process, preventing the hydraulic pump from completing the cycle.
- The crew likely misperceived the landing gear status because the 'gear down and locked' green light was extremely dim due to low voltage.
- Although the crew expressed doubts about the gear position to the tower, they did not perform the manual emergency gear extension procedure.
- The aircraft's geometry and the pilot's technique (maintaining a nose-high attitude without braking) allowed the gear to remain extended only as long as the nose remained elevated.