What happened
On May 12, 2004, a Rockwell Commander 680-F, registration EC-CTO, was performing a private flight at Cuatro Vientos Airport in Madrid. After a 12-minute flight, the pilot approached runway 28. Prior to touchdown, the pilot confirmed via cockpit indicators and a visual external check that the landing gear was down and locked.
Upon touchdown, the pilot applied light braking. Shortly thereafter, the right main landing gear began to retract without command. The pilot immediately cut engine power and fuel mixture in an attempt to maintain control. The aircraft drifted to the right, causing the lower fuselage to contact the runway surface. The aircraft subsequently veered off the runway, coming to a stop approximately 990 meters from the threshold and 26 meters from the runway edge. There were no injuries to the pilot or the passenger, though the aircraft sustained significant damage to the fuselage, the right wing tip, and the right propeller.
The investigation
The CIAIAC investigation focused on why the landing gear retracted despite the cockpit indicating a locked status. Investigators examined the landing gear assembly and discovered that the right main landing gear was not actually reaching the overcenter position required for a positive lock.
During the disassembly of the gear, investigators found that pin P/N ED12434 had been mounted incorrectly. This error prevented the gear from locking into place. Furthermore, the investigation revealed that the cockpit indicator switch had been adjusted following the incorrect installation of the pin, which created a false positive indication of the gear being locked. The investigation also noted that the same pin was incorrectly mounted in the left main landing gear, though this did not result in a retraction during this specific event.
Findings
- The primary cause of the uncommanded retraction was that the right main landing gear was not mechanically locked due to the incorrect mounting of pin P/N ED12434.
- The cockpit's green 'down and locked' light provided an erroneous indication because the indicator switch had been adjusted to compensate for the improperly installed pin.
- A contributing factor was the lack of specific instructions in the aircraft maintenance manual regarding the correct orientation and mounting of pin P/N ED12434, which likely led maintenance personnel to believe the incorrect installation was correct.
- The aircraft had a history of similar landing gear issues, including two previous incidents involving uncommanded retractions.