Flight Crew Last 90 Days 170; Flight Crew Type 10000
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude
Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition; Flight Crew Landed As Precaution
Aircraft
The flight was on time and there were no issues prior to climbout. Upon gear retraction; we saw both A system low pressure lights; initially for the engine pump followed by the electric pump light. We looked for other indications and found the right main landing gear was still in the down position and the A system hydraulic quantity was at zero. We began handling the situation per the checklist and got vectors to a holding pattern to burn off gas. The issue was with the handling of the aircraft. With half the hydraulics and no autopilot; I had difficulty staying exactly at the assigned altitude while trying to deal with the problem. I never got more than 300 feet off the altitude; but Approach Control was concerned and made several calls reference our altitude. At that point the First Officer asked for a block altitude and we were then free to deal with the problem. We eventually returned to [the departure airport] for a normal landing.
A B737 Captain reported returning to the departure airport after losing the A hydraulic system.