PMDG 747-400 pressurization system.

[sotiris 1]

Hi all,I use FS9 version and, while testing pressurization system, I noticed something for which I 'd like your opinion.We all know that as soon as cabin altitude reaches 10000 ft, this in turn will start an aural warning for the crew and won't stop unless cabin altitude drops. In the incident I am talking about, I intentionally left all pack switches to off position, I took off and waited to see when (eg in how long) would cabin altitude reach 10000 ft value. Cabin altitude started to go up but in a surprisingly low rate : the 10000 ft mark was reached no sooner than 35 min (~240 NM)later.Do you think this is normal ? Talked about it with real pilots and it appeared strange to them like was to me, so that's why I would like to hear designers' point of view. OK, this is not critical for virtual pilots' lives, just curious....Thanks, Sotiris.

[michal 44]

>mark was reached no sooner than 35 min (~240 NM)later.>Do you think this is normal ? I think it is. Based on some prior discussion on this forum about pressurization this is probably a correct behavior. In a typical unpressurized airplane the leakage of air is so high that indeed the pressure inside will always equal pressure outside but in a pressurized aircraft there will be certain delay because the cabin is sealed much better. I recall someone here who knows this aspect of the 747-400 said that in ground tests that maintenance personnel sometimes perform a 747 would "loose" its air in about 30-40 minutes so your experiment actually confirms that this aspect seems to be modeled correctly. If you wanted the 747 to behave like an unpressurized small Cessna you could force that by configuring some valves to stay open.You may also read this thread:http://forums.avsim.net/dcboard.php?az=sho...ing_type=searchMichael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg