Date: 201708
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Hydraulic Main System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Procedure
Primary problem: Ambiguous

Narrative: At cruise received HYD QTY EICAS. Reservoir (RSVR) light on left hydraulic system was illuminated. Status page indicated 43% quantity. Accomplished QRH HYD QTY procedure. Left Reservoir quantity continued to decrease slowly to 17% within 30 minutes. With regards to the note in the QRH; [we were] directed to HYD SYS PRESS-L checklist. After discussing this with First Officer; Dispatch and Maintenance [we] followed the HYD SYS PRESS checklist. Dispatch informed ATC of our condition and needs. I had the Lead Flight Attendant come to the cockpit and briefed her on the situation. No prep for evacuation was needed. I then made an announcement to the passengers of our condition and what to expect on approach and landing. I found the two checklists to be a little confusing. The HYD QTY checklist Condition: states hydraulic quantity is LOW. The note below directs you to the HYD SYS PRESS-L if left system fluid is LOST. Maintenance could not tell us at what quantity we would have no left system. Does the term LOST mean half; 40% or 100%? Some fluid was LOST and it was decreasing so we planned on the HYD SYS PRESS-L checklist. We did turn on the left system pumps when we put the landing gear and flaps down and then turned them off after a successful normal gear extension and flaps to 20 as required by the HYD SYS PRESS checklist. The Power Transfer Unit (PTU) worked normally and we had nose wheel steering upon landing. The tug was not needed but had been requested in case of no nose wheel steering. We had requested the longest runway and the First Officer made a fine landing there. The calculated landing distance was approximately 4000 ft. This problem would be helped by superior systems knowledge. The PTU uses hydraulic pressure from the right engine driven pump! I shut down the right engine as we pulled into the gate and lost nose wheel steering. Had to be towed in the last 50 feet. The manual also says on page that 'Without the right engine driven pump; PTU output may be insufficient.' Also Maintenance and I could not understand why there was 3000 PSI in the left system with the left pumps off. The Flight Manual states that the status page pressure indication will show PTU pressure when it operates.I believe the handling of the emergency went well by all team members involved. CRM was at work and crew duties [were] well defined. The verbiage in the QRH might be better thought out or at least better guidance on when to use which checklist. In the moment Fluid LOST is a bit vague and the difference in the two checklists is a flaps 30/25 landing or a flaps 20 landing.




Synopsis: B757 Captain reported losing hydraulic fluid and finding the QRH procedure to be confusing.