LOL Paul, if he behaves like a slack jawed idiot at 5000 feet, I hope
he's not conducting any official business in Air Force One.
Regulations specify that the air pressure in the cabin of a commercial
airliner must not be lower than that found at an altitude of 8,000 ft
(2,438 m). The pressure at this altitude is 1,572 pounds per square
foot or 75 kilopascals. This pressure is only about 75% that found at
sea level, which is 2,116 psf (101 kPa).
This pressure was chosen for two reasons. First, the skin of the
aircraft is designed to maintain its shape given the difference in
pressure internal and external to the cabin. Aircraft manufacturers
want to keep that difference as small as possible because it reduces
the amount of structure needed to maintain the integrity of the
aircraft's shape. The less structure required, the lighter and less
expensive the plane will be.
Ideally, the internal and external pressures would always be equal to
minimize the structural weight. However, the pressure cannot be too
low or passengers could suffer from altitude sickness or pass out from
oxygen deprivation. Most cases of altitude sickness occur at altitudes
greater than 10,000 ft (3,050 m) and oxygen deprivation is typically
not a concern below 14,000 ft (4,265 m).
The altitude of 8,000 ft was chosen as a tradeoff to satisfy these two
requirements. The pressure at this altitude is low enough that it
significantly reduces the amount of structure needed to maintain the
plane's shape yet high enough that it prevents altitude sickness among
the passengers. The pressure on a specific aircraft may vary as
different manufacturers offer different environmental systems aboard
their planes. In general, most airlines maintain an internal pressure
comparable to that found at 6,000 to 8,000 ft (1,830 to 2,440 m). The
pressure will obviously increase at lower altitudes to equalize with
the external pressure encountered at takeoff and landing.
http://www.aerospaceweb.org/question/atmosphere/q0206a.shtml
Air Force One is a 747.
There is a general belief that the pressure in the cabin (or, as it is
known, cabin altitude) is equivalent to that at sea level. This is not
the case. Cabin altitude can fluctuate from 5,000 to 8,600 feet in
cruise levels and is dependent on many variables, including the load
factor, fuel burn, the aircraft’s age and model and , above all, the
airline or captain’s preference.
In the instance of an aircraft cruising at an altitude below its
operational ceilings, there is a choice. The pilot can either select
the maximum cabin differential pressure (about 5,000-6,000 feet) to
increase the comfort of the passengers, or make things easier on the
cabin structure (what is known as “prolonging the cabin’s fatigue
life”) by keeping the differential pressure at a setting of around
8,000 feet.
The optimum cabin altitude for the 747-400 at flight levels of
29,000-41,000 feet is 8,000 feet, according to Bob Fletcher, Head
Flight Operations Engineer of Air New Zealand. The Concorde was an
exception because its cabin altitude could be maintained at 5,000 feet
due to its high cabin pressure differential.
http://www.aviation-health.co.uk/news/browse.php?load=aibs.html#PRESSURISE