Narrative:

Aircraft X did an air return to ZZZ due to a hydraulic leak in the a system after takeoff. This aircraft had just undergone maintenance to replace the #1 engine hydraulic pump and both the ca (captain) and first officer (first officer) did a walk around paying close attention to this area. No abnormalities were found. Upon arriving at the aircraft; both hydraulic systems showed 100%. Once the hydraulic pumps were turned on during pushback; the B side remained around 100% and the a side dropped to ~85% then stabilized for the rest of the taxi. During gear retraction after takeoff; the master caution and hydraulic lights flickered then immediately went out. I was flying so the ca pulled up the system page on the CDU and saw that the a side dropped to ~40%. By the time the aircraft had climbed to 12;000; the pressure had dropped to ~34% and was steadily decreasing. The ca asked me if I agreed with returning to ZZZ and I did. I continued to fly while the ca coordinated with ATC; the flight attendants; and made a PA announcement. Once the aircraft was established on the localizer for runway xx; the ca took over the duties of PF (pilot flying) and made the overweight landing. The hydraulic and master caution lights flickered again on gear extension and on the landing rollout. At no point did the hydraulic annunciator remain illuminated nor illuminate during the recall. After landing; the a system indicated 20% RF (refill) and the aircraft taxied off the runway and back to the gate without any further issues.

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Original NASA ASRS Text

Title: B737 flight crew reported a decrease in hydraulic quantity and pressure during climb resulted in a return to the departure airport.

Narrative: Aircraft X did an air return to ZZZ due to a hydraulic leak in the A system after takeoff. This aircraft had just undergone maintenance to replace the #1 engine hydraulic pump and both the CA (Captain) and FO (First Officer) did a walk around paying close attention to this area. No abnormalities were found. Upon arriving at the aircraft; both hydraulic systems showed 100%. Once the hydraulic pumps were turned on during pushback; the B side remained around 100% and the A side dropped to ~85% then stabilized for the rest of the taxi. During gear retraction after takeoff; the master caution and HYD lights flickered then immediately went out. I was flying so the CA pulled up the SYS page on the CDU and saw that the A side dropped to ~40%. By the time the aircraft had climbed to 12;000; the pressure had dropped to ~34% and was steadily decreasing. The CA asked me if I agreed with returning to ZZZ and I did. I continued to fly while the CA coordinated with ATC; the flight attendants; and made a PA announcement. Once the aircraft was established on the LOC for runway XX; the CA took over the duties of PF (Pilot Flying) and made the overweight landing. The HYD and master caution lights flickered again on gear extension and on the landing rollout. At no point did the HYD annunciator remain illuminated nor illuminate during the recall. After landing; the A system indicated 20% RF (refill) and the aircraft taxied off the runway and back to the gate without any further issues.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.