What happened
On December 5, 2005, a BEECHCRAFT F-33 A, registration EC-FXZ, was conducting a visual navigation training flight from Cuatro Vientos to the Roblediliio de Mohernando airfield. The flight was operated by a flight school and carried a student pilot and an instructor.
During the fourth landing of the flight, which was intended to be a full-stop landing, the student pilot confirmed that the three green lights indicating the landing gear was down and locked were illuminated. The landing itself was performed correctly without any bouncing. However, as the student pilot applied the brakes, a metallic grinding noise was heard. Shortly after, the landing gear collapsed, causing the propeller to strike the runway surface. The engine stopped immediately, and the aircraft slid along the runway until it came to a halt. The crew evacuated the aircraft following the shutdown of fuel and electrical systems.
The investigation
The investigation focused on the mechanical state of the landing gear extension/retraction system and the electrical motor. The aircraft sustained damage to the propeller blades, which were bent backward from the impact. The landing gear doors showed significant wear from friction, and several retraction system bars were deformed due to buckling. Additionally, the electric motor responsible for the gear movement had a burnt winding.
Investigators examined the gear actuator, which utilizes an electric motor, a worm gear, and a cross-arm mechanism to extend the main and nose gear. Because the three green lights were illuminated prior to landing, the investigation ruled out a simultaneous failure of all three legs due to gear breakage. The burnt motor winding suggested that the electrical current was never cut off by the limit switch, meaning the motor remained under load.
Findings
- The electric motor's windings were burnt, indicating an electrical overload.
- The investigation established that the landing gear had not been fully extended and locked prior to touchdown.
- Because the gear was not fully locked, the limit switch failed to cut power to the motor, causing the motor to continue drawing current and overheat.
- The application of brakes created additional mechanical stress on the partially extended gear, leading to the buckling of the retraction bars and the subsequent collapse of the gear.