B747 Undifferentiated or Other Model
Workload; Troubleshooting; Training / Qualification; Situational Awareness
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Departure Airport; Flight Crew FLC complied w / Automation / Advisory; General Maintenance Action
Aircraft
While on climbout; the HYD OVHT SYS 4 EICAS message came on. We got out the QRH and went through the checklist. As we waited to see if the message would go away; the Captain got on SATCOM with Dispatch and Maintenance Control. During their discussion; the message did go out. Per the checklist; at that point we continued normal operations. We discussed scenarios in case the message came back. Because of the ALTN gear extension in the checklist; once we put the gear down; it had to stay down. So we thought neither alternates were viable options. The weather at destination required an alternate so a missed approach there could mean a gear down flight to the alternate for which we did not have the fuel. And a landing anywhere would park the aircraft until it could be fixed. We decided the best options were an enroute diversion or a return to the departure airport. The Captain had given Dispatch a heads up during his first discussion with them as to our thinking. The EICAS message did return and the Captain got back on SATCOM. Maintenance suggested turning on the Engine Driven Pump. As that was not in the procedure anywhere; we elected not to start improvising. It was determined by all parties the best course of action would be a return to the departure airport. We got an ATC clearance and advised them of our need to dump fuel. We dumped about 198;000 LBS to get below max landing weight; which took about an hour. At the suggestion of Maintenance Control; the Captain used his Emergency Authority to modify the QRH procedure for alternate gear extension and initial flap selection. When we had first done the HYD OVHT SYS 4 procedure; it had taken approximately 15 minutes for the system to overheat when the Demand Pump was switched back to AUTO. So 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; the Captain selected Demand Pump 4 to AUTO for about 1 minute to let the gear and flaps 5 out normally. Once that was done; the pump was again selected off. During this procedure; the HYD SYS page on the lower EICAS was monitored to make sure the Number 4 hydraulic temperature stayed in the normal range; which it did. The final flap selection was conducted in secondary mode and the aircraft was configured per QRH procedure. Dispatch supplied landing data for runway at departure airport and a normal landing was made.
A B747 EICAS alerted HYD OVHT SYS 4 during climb after takeoff so following extensive troubleshooting the aircraft returned to the departure airport for maintenance.