G-Dawg: i thought the flt/gnd switch had air logic, hence if you forgot to put it to flight before t/o it wouldn't matter, however a few days ago i was shown this not to be the case, at least in the initial climb. I've looked for some info on it, can someone shed some light???
Yes it does have air logic in that if you place the flt/gnd switch to gnd while in pressurised flight then it won't depressurise. ie it is useless once airborne.
The point of the switch is to pressurise the cabin to an altitude of 200' below the departure airfied elevation before you take off. so placing the switch to flt before departure will pressurise the cabin slightly. this helps the aircraft structurally ie its a more solid object and also helps the passangers by providing a more comfortable transition to pressurised flight.
If the switch is left to gnd before departure it's not a big deal however the aircraft won't be pressurised slightly before the departure. soon as the air/gnd sensor detects flight mode then the cabin pressurises anyway and the flt/gnd switch is useless until touching down again.
the landing is pretty much the same.. the aircraft will remain slightly pressurised for the landing. if the flt/gnd switch is forgotten in GND then as soon as the aircraft touches down it'll depressurise. if it is in flt then it will remain in the slightly pressurised state until the flt/gnd switch is switched to gnd.