Incident Overview
The captain reported that while in cruise flight at flight level 330, the crew received a master caution light and a hydraulic system 1 low pressure warning, accompanied by warning lights for the outboard ground spoilers, outboard spoilerons, and outboard spoilers. The hydraulic fluid quantity and temperature readings were normal, but the system pressure was decreasing.
Crew Actions
In response, the crew executed the emergency checklist and continued the flight to Denver using the backup 1B system. During final approach and landing, the captain noted a loss of number 1 system pressure and quantity. The crew subsequently shut off the 1B system and completed the landing. After landing, they shut down the number one engine and taxied to the gate.
Post-Incident Examination
A post-incident examination of the airplane's number 1 hydraulic system revealed that the hydraulic pump had come apart internally and seized. Metal fragments were found in the hydraulic filters and lines. Further inspection of the hydraulic pump showed that several piston shoes in the pump's hanger and piston subassembly had disintegrated. The resulting metal fragments caused damage to the hold-down plate, the hanger, and other internal components, leading to the pump's seizure.