B767-200
Aircraft Equipment Problem Critical
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Manuals; Human Factors; Aircraft
While climbing through 2;000 FT; Captain noticed that aircraft was not pressurizing. [I] requested to level off at 6;000 FT to work the problem. After determining that aircraft was not going to be able to pressurized; Captain declared an emergency for an overweight landing and requested vectors for a return. At this point I took over communications with ATC and flew the airplane while the Captain coordinated with Dispatch and Operations. We were vectored around and executed the ILS. Touchdown was smooth and brakes were not applied until the aircraft slowed to 60 KTS on full reverse. We returned on our own power to the gate where later on Maintenance determined the aircraft was out of service. All required entries for the Overweight Landing and pressurization malfunction were entered in the logbook as required.
Aircraft had an existing placard for the equipment cooling valve. During the preflight the First Officer confirmed that the outboard valve was closed and its circuit breaker was pulled and collared. After takeoff; climbing through 3;000 FT I noticed that the outflow valve was fully closed and the cabin altitude was climbing as fast as the aircraft. The aircraft was leveled at 6;000 FT and ATC notified that we would be returning. I coordinated with dispatch; Operations and the Flight Attendants for our air interruption. An emergency was declared and ARFF was requested. We made an overweight landing with an aircraft weight of 289;000 LBS; 19;000 LBS overweight. Brakes were not used in the rollout until the ground speed was 50 KTS. The emergency was terminated at the end of the landing rollout and taxi to the gate was normal. Our mechanic confirmed that the outboard valve was now indeed open.Of greatest interest here is the question of how a correctly placarded valve; with all maintenance procedures followed; could have become energized with the circuit breaker pulled. I suspect that the valve motor was getting an intermittent short to ground. The MEL and Maintenance Procedures Manual need to be changed to require that the cannon plug be pulled; so there is no possibility of the valve opening. This could have happened at FL390; a much more serious situation.
B767-200 flight crew reports being dispatched with an existing placard for the equipment cooling valve. The valve was confirmed closed during preflight and the circuit breaker collared in compliance with MEL procedures. After takeoff the aircraft will not pressurize and the flight returns for an overweight landing. Maintenance confirms that the equipment valve is now open.