B747 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 150; Flight Crew Total 20000; Flight Crew Type 10000
Situational Awareness
Aircraft Equipment Problem Less Severe
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Aircraft; Weather; Human Factors
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. Contacted Dispatch via SATCOM with patch to Maintenance Control. Discussed additional trouble shooting options with [Maintenance Control] and elected not to conduct further trouble shooting procedures as aircraft was in a stabilized configuration. Discussed aircraft status with Maintenance Control and Dispatch regarding operational impact of in operative systems. 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 an alternate. Planned fuel at destination would be insufficient for a gear exte nded diversion to this alternate. 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. In coordination with Maintenance Control and Dispatch; I determined a return to be the safest course of action. I requested and received revised ATC clearance for return. Notified ATC of a planned fuel jettison and conducted Fuel Jettison procedure per QRH. Jettisoned approximately 198.0 pounds fuel and reduced aircraft to below maximum structural landing weight.At the suggestion of Maintenance Control and based on my systems knowledge; I exercised my Captain's 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 4 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 aircraft was configured per HYD OVHT SYS 4 QRH procedure. Dispatch provided landing data for landing on longest available runway. Normal landing below maximum landing weight.
B747 Captain reports a HYD OVHT SYS 4 EICAS message during climb. QRH procedures are applied; the overheat returns and the decision is made to return to the departure airport.