What happened
On March 8, 2001, a Cessna 525 Citation Jet was conducting an IFR flight from Mannheim to Hamburg. During the approach to runway 15 at Hamburg Airport, the pilot reported landing gear issues to the tower. Although the tower controller observed all wheels in the down position during a flyby, cockpit indications continued to show an uncertain gear status.
During the landing at approximately 21:20 CET, the right main landing gear collapsed immediately upon touchdown. The pilot managed to use directional control to prevent the right wing from dragging for a significant distance, maintaining the aircraft on the runway for over 1,000 meters. However, the aircraft eventually veered off the runway, 30 meters to the right of runway 15, and came to a stop 300 meters before the intersection with runway 23. The aircraft sustained heavy damage, and a runway boundary light was destroyed. The pilot was uninjured.
The investigation
The BFU investigation focused on the hydraulic system and the pilot's emergency procedures. Investigators examined the aircraft's hydraulic components, including the nitrogen bottle used for emergency gear extension. Physical evidence at the cockpit showed that while the gear handle was in the DOWN position and the emergency T-handle had been pulled, the secondary red knob—intended to trigger the nitrogen blow-down for positive locking—had not been operated.
Technical analysis of the hydraulic system revealed that a solenoid loading valve had failed. Specifically, a loose metal filter screen had become dislodged within the valve cylinder, causing the valve to remain stuck in the open position and resulting in a total loss of hydraulic pressure to the landing gear, flaps, and speed brakes.
Findings
- The primary cause of the hydraulic failure was a defective solenoid loading valve caused by a loose internal filter screen.
- The pilot failed to consistently follow the manufacturer's recommended emergency procedures for securing the landing gear.
- The manufacturer's instructions for the auxiliary gear control were found to be unclear, particularly regarding the distinction between the T-handle and the secondary knob.
- The pilot's spontaneous radio communications suggested a misunderstanding of the required steps, as he believed pulling the T-handle alone was sufficient to extend and lock the gear.
- At the time of the accident, the maintenance facility was not yet aware of a recent Service Bulletin recommending the replacement of this specific valve version.