What happened
On February 6, 2003, a Rockwell Commander 680-F, registration EC-CTO, departed from Cuatro Vientos Airport in Madrid for a flight intended to verify a student's competency. Shortly after takeoff, the pilot attempted to retract the landing gear but observed that the cockpit indication showed the right gear remained down and locked (green light on). After two unsuccessful attempts to cycle the gear, a third attempt resulted in a significant drop in hydraulic pressure to 700 psi, at which point the gear began to descend even with the lever in the up position.
The crew declared an emergency and requested priority to return to the aerodrome, reporting hydraulic system issues. Following a visual confirmation from the tower that the gear was down, the pilot performed a series of maneuvers to attempt to lock the gear, eventually reporting that the gear appeared locked. However, hydraulic pressure had dropped to 350 psi, which was insufficient for effective braking.
Upon landing at 16:33 UTC, the aircraft traveled between 100 and 200 meters before the right main gear retracted. This caused the aircraft to skid, resulting in significant damage to the right wing, the propeller, and the lower fuselage, as well as a fuel leak. There were no fatalities and no injuries among the three occupants.
The investigation
The CIAIAC investigation focused on the hydraulic system failure and the failure of the gear to remain locked. Post-accident inspections revealed a perforation in the hydraulic line connecting the up-gear check valve to the main gear locking cylinders. This leak caused the rapid depletion of hydraulic fluid during the crew's attempts to cycle the gear.
Investigators also examined the cockpit indications. They found that the right main gear down-and-locked switch was providing erroneous information. The switch's stem was not moving freely due to dirt accumulation and a lack of lubrication, which caused the green light to remain illuminated regardless of the gear's actual position.
Regarding the gear retraction during the landing roll, the investigation determined that the pneumatic system was functional and capable of extending the gear even without hydraulic pressure. Therefore, the retraction was not caused by the hydraulic leak itself, but rather by a failure of the gear to properly lock in the down position.
Findings
- The primary cause of the hydraulic pressure loss was a perforation in the hydraulic line serving the gear-up locking cylinders.
- The cockpit indication for the right main gear was unreliable because the down-and-locked switch was malfunctioning due to dirt and lack of lubrication.
- The right main gear failed to lock in the down position, likely due to excessive friction or issues with the overcenter locking components (such as the rubber elements), potentially caused by a lack of recent lubrication or maintenance during the aircraft's period of low utilization.
- The hydraulic fluid depletion occurred rapidly during the crew's repeated attempts to cycle the landing gear following takeoff.