I have a few questions about pressure change in a passenger aircraft.
1) I suppose the pressure inside the plane is being lowered as the plane takes off and climbs toward its designated altitude, and the opposite is being done when the plane lands. Is this correct? What is the pressure that is maintained inside the plane when it is at an altitude of about 10,000 meter?
2) After the touch-down and when the plane comes to standstill and the passengers stand up and are ready to leave, it still takes a while before the door of the plane is opened. Do they need those moments to slowly increase the internal pressure so that it will be the same as the external one?
I think the simulated altitude inside a plane is something like 6000-8000 ft whenever the plane is above that level. I suspect that below the simulated altitude, the pressure inside is the same as the pressure outside.
No. The delay is for the airport people to position the jetway and do whatever else they need to do outside the plane before people get off.
from what we were taught in pilots school, and not from direct design experience:
the pressurized aircraft cabin is basically an aluminum balloon with you on the inside - when cabin is at atmospheric sea level and the outside is at the nil pressure of 35,000 feet, it has 15 psi pushing out. Basically, anything you can do to reduce that pressure reduces the skin stress from that difference accordingly, which then either increases the safety factor or reduces the weight of any extra aluminum needed in the skin. I understood that into the 80's it was usual practice to keep the cabin pressure at half an atmosphere (5000 feet equivalent), and during the last of the reagan years, the aging US fleet was given more years by allowing the equivalent pressure to go to 6000 feet. I do not know if "foreign fleets" use the 6000 foot equivalent rather than the 5000 . (Virgin Air does not reduce atmospheric pressure to half, yet maintains the same safety factor. I do not know the method they use - speed, altitude, heavy skin on their planes, less life on a plane, etc.) That pressure change is supposed to be why your feet have a hard time going back into your shoes on long flights, and why you have to wait to fly after scuba diving - extended low pressure.
I have seen the gate attendants standing and waiting as well, and I assumed that equalization safeties "designed in" may take some time, sometimes (wouldn't want the door to blow in on the attendants.) since there is plenty of time for the air pressure to change during landing and taxi. It may also be the seal on the door is pressure based, and the seal needs to deflate sufficiently in order for the door to be removed
I always wondered how they kept the bags of snacks from ballooning out........
You have received all the good reasonable standard answers. I will give the one I thought of, which is the only reason I would imagine airlines would make us listen to screaming children and suffer pounding headaches for:
An airframe who's skin is kept under internal pressure will not "oil can". Oil canning will result in rapid fatigue failure at joints near the areas popping in and out. I suspect the internals are kept above atmospheric (to some extent) while the door is closed, or at least until the aircraft is no longer expected to take off.
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