Incident Overview
During the approach, the main hydraulic system lost pressure. The pilots selected the auxiliary hydraulic system on, continued the approach, and extended the landing gear using the emergency landing gear extension procedures. During the landing roll, about two-thirds down the runway, the pilots noticed abnormal brake operation and then turned onto a taxiway to clear the runway. Once on the taxiway, the captain was unable to stop or steer the airplane. It proceeded across a parallel runway and into an adjacent field, where it struck a metal beam.
Postaccident Examination
Postaccident examination revealed brake system continuity with cockpit controls. Tires, brake assemblies, and brake pads were intact and undamaged. Hydraulic lines from the pump to wheel brakes were intact. No hydraulic fluid leaks were observed. The hydraulic fluid reservoir was about one-quarter full. Testing of the two hydraulic pumps showed they were functional, and no mechanical failures or anomalies that would preclude normal operation were noted.
Hydraulic System Emergency Procedures
The airplane's hydraulic system failure emergency procedures state that if hydraulic pressure is lost, the electrically driven hydraulic pump should be reset. If pressure is not restored, the primary hydraulic system should be disengaged and the landing gear lowered using emergency extension procedures. After gear extension, the auxiliary hydraulic system should be selected on for landing. However, the pilots stated they did not attempt to reset the electric hydraulic pump and performed the emergency gear extension with the auxiliary hydraulic pump engaged. It is likely that failing to select the auxiliary system off before gear extension caused hydraulic pressure in the auxiliary system to dissipate, leaving only the emergency brake accumulator for braking. The number of emergency brake applications depends on accumulator charge, which may deplete quickly.
Emergency Braking and Runway Exit
The emergency braking procedures state that as soon as the airplane is safely stopped, pilots should request towing assistance. However, the pilots did not stop on the runway despite about 3,900 ft remaining; instead, they turned off at an intersection, resulting in loss of directional control.