Aircraft Equipment Problem Less Severe
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Aircraft; Procedure
After a 2 hour delay for aircraft to be placed in service after an overnight 'A' check. Maintenance Technician was rebalancing hydraulic A and B fluid levels. It was replenished to 95%. After reaching cruise flight at FL350 I began to monitor Hydraulic System quantity and pressure. I alerted Captain to A level at approximately 74% and started to drop progressively 1-2% in the next several minutes. Captain gave aircraft flying duties to myself and contacted company Maintenance and Dispatch via radio. After 2 separate conversations with company and upon reaching the quantity level of approximately 62% on A Hydraulic system; the Captain felt the safest course of action was an air return to the departure airport. I agreed. It afforded us the longest runway available and premier Crash/Fire Rescue services. We reviewed QRH and briefed flight attendants/passengers/Cockpit Jumpseat Rider. Captain assumed flying duties and I resumed pilot monitoring duties. An emergency was declared and ATC cleared us back direct. Minimal aircraft maneuvering was requested. A flaps 30 autobrakes 3 landing was performed without incident and Crash/Fire Rescue advised no exterior negative mechanical indications were observed. We taxied to gate and deplaned passengers and affected a logbook entry as to the aircraft condition.
B737 First Officer reports receiving an aircraft from Maintenance after an 'A' check. At FL350 Hydraulic System A quantity is noted to be solely decreasing and crew elects to return the departure airport.