B737 NG flight Crew reported a Hydraulic System A EDP pressure low light on during cruise. The flight crew elected to continue the flight. The A Hydraulic System subsequently lost most system quantity. On descent; The System B EDP also failed. The flight crew requested priority handling and made a precautionary landing at the destination airport.
Synopsis
B737 NG flight Crew reported a Hydraulic System A EDP pressure low light on during cruise. The flight crew elected to continue the flight. The A Hydraulic System subsequently lost most system quantity. On descent; The System B EDP also failed. The flight crew requested priority handling and made a precautionary landing at the destination airport.
Narrative
Just prior to ETOPS airspace ZZZ-ZZZ1 we got a Hydraulic A Engine Driven Pump low pressure light. Ran the QRH and turned the pump off. Coordinated with Dispatch and Maintenance over HF and decide to continue as we had normal pressure and adequate quantity. Just prior to the CP; the reservoir started fluctuating and dropped to 20%. still had 2;950 PSI. over the next 2 hours the quantity fluctuated between 0 and 7%. we discussed the possibility of losing the associated electric pump and the whole A system and looked over the QRH so we were prepared for it on descent into ZZZ1. Both pressures were approximately 2;950 PSI most of the flight. On descent to ZZZ1 we got system B Engine Driven Pump low pressure and ran the QRH again. Turned the pump off and requested priority handling. Requested XXL and notified Dispatch and Flight Attendants. Gear came down slower than normal and flaps as well. We configured normal and landed normal. Brakes worked normal as well as nose wheel steering. System B quantity and pressure seemed to remain normal. Taxied to the gate and Maintenance opened the #1 engine cowl to find hydraulic fluid everywhere. I left before they addressed the #2 engine.
Second reporter narrative
The ENG 1 hydraulic low pressure light illuminated in cruise flight. We ran the checklist from the QRH; which only says to turn the pump off. Within approximately 30-60 minutes; the quantity in the A system dropped to 20%. This is commensurate with the level of the standpipe in the A reservoir. It was our thinking that the engine-driven pump in the A system failed and a leak occurred in that pump or associated lines. Over the course of the flight; the quantity in the A system fluctuated between 13-0%; I surmise because of cold-soaking of the remaining fluid. At all times the electric hydraulic pump in the A system remained on with good pressure at 3;000 PSI. We talked on HF radio with Maintenance and Dispatch. They couldn't think of anything else we could do. It was at times difficult to understand them; which is consistent with typical performance of HF. SATCOM would have been a welcome tool.We reviewed checklists for possible scenarios; including loss of A system pressure; and even loss of A and B system pressure; and we discussed possibilities. After evaluating all options; we decided to press on to ZZZ1. The B system was working fine; the A system still had good pressure; and there were no issues with the Standby hydraulic system. We were expecting a normal landing. At worst; we thought we may have to do a manual gear extension if the A system electric pump stopped producing good pressure.At top of descent into ZZZ1; at the exact moment the thrust levers retarded for descent; the ENG 2 hydraulic low pressure light illuminated. We ran the QRH checklist and turned that pump off as well. We were both a bit confused as to why the B system engine-driven pump would fail. It was unexpected. Because we now had two major pump failures in separate systems; we requested priority handling with ATC and requested Runway XXL; the longest runway. I sent an ACARS message to Dispatch; and did a briefing with the Purser. I also made a PA to the passengers and said we expected a normal landing; but they may see some emergency equipment standing by. We configured early; and flaps and gear slowly came down. Good pressure and quantity were maintained on the B side with the electric pump throughout the remainder of the flight. A side hydraulic pressure also remained at 3;000 PSI. Last I saw; quantity on the A side was 11% and B side was at 96%. Landing and taxi in were uneventful.On the ground; the Mechanics opened the #1 engine cowling and hydraulic fluid was dripping out. They also seemed confused as to why the B system engine-driven pump would have failed. I plan to follow up on that with Maintenance to learn as much as I can.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.