Incident Sequence
During descent, the aircraft experienced a complete hydraulic system failure. The landing rollout was carried out under these conditions, during which the airplane ran off the side of the runway. It subsequently collided with a manhole cover, causing the nose gear to collapse.
Mechanical Failure
Examination revealed that the power transfer unit shutoff valve, part number 240695, had failed. One of the dual valve body halves had separated at the mounting plate. The source notes that the valve had a known history of failures, and the manufacturer had made a kit version of a fix available.
Operational Considerations
The flight manual contains cautions for landing with no hydraulic power. It advises that increasing amounts of reverse thrust significantly reduce rudder effectiveness. In the event of directional control problems, pilots are instructed to reduce reverse thrust as required and select forward idle if necessary to maintain or regain control. Digital flight data recorder (DFDR) readouts showed that reverse thrust greater than idle was applied during the landing rollout.