What happened
On August 15, 2007, a Lancair IV-P, registration N369BX, was performing a private flight landing at Treviso S. Angelo Airport (LIPH). The flight had proceeded without incident from its departure point in Siena. During the final approach, the pilot attempted to deploy the full flaps; however, the flap lever was unresponsive. The pilot interpreted this lack of movement as a hydraulic system failure. Because the landing gear was already extended and the green indicator lights remained illuminated, the pilot proceeded with the landing.
During the landing roll, the right main landing gear unexpectedly retracted. This loss of support made it impossible to maintain directional control on the ground, causing the aircraft to veer laterally off the runway and come to a stop approximately 3 and 30 meters beyond the runway edge. The pilot sustained no injuries, though the aircraft's right winglet was damaged.
The investigation
The ANSV investigation focused on the hydraulic system and the mechanical failure of the landing gear. Investigators examined the aircraft's maintenance records, which showed that periodic inspections had been performed regularly and no previous malfunctions related to this event had been reported.
Technical testing conducted after the accident revealed a total failure of the hydraulic pump. During subsequent functional tests following the replacement of the pump, investigators discovered that the pressure switch controlling the system pressure had been incorrectly adjusted. The system was maintaining a pressure of 1500 psi, significantly exceeding the prescribed operating pressure of 1100 psi. As the annual inspection does not involve adjusting this pressure switch, investigators concluded that the incorrect setting likely occurred during the initial assembly of the aircraft.
Findings
- The aircraft veered off the runway due to the inability to control the trajectory following the uncommanded retraction of the right main landing gear.
- The retraction was caused by a loss of hydraulic system pressure resulting from the failure of the hydraulic pump.
- The premature failure of the pump was likely caused by the overpressure induced by the incorrect setting of the hydraulic pressure switch.