B747-400
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 200; Flight Crew Total 21000; Flight Crew Type 3000
Situational Awareness; Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Aircraft
During initial climb; HYD OVHT SYS 4 EICAS displayed. Accomplished HYD OVHT SYS 4 QRH. Per procedure; when HYD OVHT SYS 4 messaged blanked; selected Demand Pump to AUTO. After several minutes; HYD OVHT SYS 4 EICAS displayed again. We contacted Dispatch with a patch to Maintenance Control; discussed the operational impact of inoperative systems and elected not to conduct further trouble shooting procedures as aircraft was currently in a stabilized configuration. My primary concern was the need for alternate gear extension at destination which would preclude gear retraction in the event of a go around or missed approach. Destination weather forecast for our arrival required naming ZZZ as an alternate. Planned fuel at destination would be insufficient for a gear extended diversion to ZZZ. Based on lack of adequate fuel for a diversion from planned destination to the named alternate; I made the decision not to continue to destination. [We all agreed] a return to our departure airport to be the safest course of action. We requested and received an ATC clearance for our return and coordinated the dumping of 198.0 pounds of fuel to reduce the aircraft to below maximum structural landing weight. At the suggestion of Maintenance Control and based on my systems knowledge; I exercised Emergency Authority to modify the QRH procedure for alternate gear extension and initial flap selection. During the initial HYD OVHT SYS 4 procedure; it took approximately fifteen minutes for the system to overheat after returning the Demand Pump to AUTO per the procedure. To avoid the mechanical stress of a free fall extension of the wing gear and to reduce cockpit workload by simplifying the flap extension procedure; I selected Demand Pump four to AUTO for approximately one minute while extending the gear normally and selecting flaps 5. Once the gear and flaps were in this position; I turned off Demand Pump 4. During this time I monitored the HYD SYS page and noted System 4 hydraulic temperature remained in the normal range with no EICAS displayed. Final flap selection was conducted in secondary mode and the aircraft configured per the HYD OVHT SYS 4 QRH procedure. Dispatch provided landing data for landing on longest available runway and a normal landing below maximum landing weight was accomplished.
A B747-400 flight crew dumped fuel and returned to their departure airport after suffering an Hydraulic System four overheat.