R/W question about 747 cabin pressurization -

[Guest Ricardo Sevarant]

Hello PMDG People,The PMDG 747 manual details that the 747-400 pressurization system (with PACKS on AUTO), begins to pressurize the cabin when a sensor detects groundspeed at 60+ knots on takeoff roll. I know that the pneumatic systems on some other fleet type aircraft pressurize the cabin as soon as the PACKS are set after engine start.Question: Do later models of aircraft have the groundspeed sensor system for better fuel economy or is this system incorporated for enhanced safety in the event of emergency evacuation (I.E., the aircraft wouldn't have to be de-pressurized on the ground so the flight attendants could more easily open the passenger doors). Thanks!

[Qavion 19]

Rico...At 65kts, the cabin is pressurized to a pressure equivalent to 50 (fifty) feet below airport altitude. Even if this cabin pressure command wasn't somehow automatically cancelled when the takeoff was aborted, I'm sure the cabin crew are quite able to overcome a hundredths of psi extra pressure on the door.Also, flight crew procedures for evacuation involve the manual operation of the outflow valves to full open to ensure there is no residual pressure.There is a modified pressurization schedule for when the aircraft takes off and has to return to the airport, but so far I haven't been able to find one for an aborted takeoff on the ground. I had a vague recollection of there being one, but it may have been for a different aircraft.Hope this helps.Cheers.Q>

[Guest Ricardo Sevarant]

Hi there Q:I'm familiar with your alter-ego, so I'm well aware of your professional credentials in providing me with this information :) Always great to see you here in the forums.Thank you very much for the info! I love learning about R/W procedures with these complex aircraft. Cheers,