B747 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Time Pressure
Aircraft Equipment Problem Critical
Flight Crew Overcame Equipment Problem; Flight Crew Returned To Departure Airport; General Declared Emergency
Procedure; Aircraft
Climbing through 3;000 FT; we received an Outflow Valve L EICAS message. This had been written up several times in the past; and it appeared to be a nuisance message because the pressurization was operating normally when we looked at it. Because of this fact and the high workload after departure; I elected to delay running the procedure for a few minutes. Immediately after climbing through 10;000 FT; we received a Cabin Altitude warning. We immediately requested and were given clearance to 8;000 FT. We ran the appropriate checklist and were unable to regain control of either outflow valve in Auto. Manual worked as expected. The cabin altitude did not exceed 11;300 FT. We returned to [the departure airport] for repair after dumping approximately 120;000 pounds of fuel.
No additional information
The pilots of a B747 observed an outflow valve fault during climb; but elected to continue the climb due to workload and considering the previous maintenance history. When they received a cabin altitude warning; they requested a lower altitude and attempted to remedy the issue per the flight manual. This was unsuccessful; so they dumped fuel and returned to the departure airport.