What happened
On June 18, 2008, a privately operated Cessna P210N, registration EC-KNF, was performing a business flight from Sabadell to the Casarrubios del Monte Aerodrome. While established in the airport traffic pattern, the pilot attempted to extend the landing gear. Although the electric motor for the gear mechanism operated, the cockpit indicator failed to show the gear as down and locked.
The pilot performed several attempts to cycle the gear, including using the emergency extension procedure, but the green indicator light remained unlit. After visually confirming that the main gear had deployed and receiving confirmation from ground personnel that the nose gear appeared extended, the pilot proceeded to land on runway 26.
During the landing roll, the pilot applied the brakes. At that moment, the nose gear collapsed, causing the nose of the aircraft to impact the runway. The aircraft continued to taxi on its main gear and the nose until it came to a stop a few meters further along the runway. The pilot and one passenger were able to exit the aircraft without injuries.
The investigation
Investigators examined the landing gear system and found that the nose gear locking mechanism relies on two hooks attached to the gear that grab two pins located on the head of a hydraulic actuator. The inspection revealed an interference between these locking pins and the nut at the end of the actuator stem. This physical obstruction prevented the actuator from reaching the end of its stroke, which in turn prevented the hooks from engaging the pins.
Upon disassembling the actuator, investigators discovered that both locking pins were broken at the level of the circumferential notch. This breakage caused the pins to displace into the actuator stem area, creating the interference.
Further investigation into the aircraft's maintenance history revealed that a previous flight a few days prior to the accident had experienced a similar lack of gear indication during an approach to Córdoba. Although the aircraft had been inspected at a workshop following that incident, no anomalies were found at that time, suggesting the pins were already broken during that inspection.
Findings
- The nose gear collapse was caused by the breakage of the two landing gear locking pins, which allowed them to displace from their housing and interfere with the actuator.
- The manufacturer had previously issued Service Bulletin SEB95-20, which addressed known failures regarding the breakage of these specific locking pins. The bulletin recommended inspecting the pins every 200 hours or replacing them with a redesigned version.
- The aircraft's maintenance records showed that the service bulletin had not been implemented.