747-400 Freighter Fire Suppression
According to the operations manual, if the Main Deck Cargo Fire ARM & DEPRESS switches are pushed, the aircraft goes into a partial decompression.
Two packs are shut down and the Main Deck cabin altitude target becomes 25,000 feet (controlled by the CPC in command). However, the manual says that the Upper Deck enviroment is comfortable.
How is this possible? With, say an Upper Deck cabin altitude of 8,000'(?) and a Main deck cabin altitude of 25,000', I estimate a differential pressure of 5~6psi. The force on the upper deck door at the top of the stepladder would be over 10,000' lbs.
Have I miscalculated? (or overlooked something)
Thanks.
Cheers.
NSEU.