Ka8 is of course right..
There are systems on a plane,other then air conditioning or anti-ice that require air from the bleeds to properly work i.e. hydraulics or water system should be pressurized to properly function.
If you have a bleed trip off-the valve will remain closed,if in AUTO.
Then you select the pack switch to off-thus causing the valve to open (if in AUTO)
The reason for this is, not to be able to use the wing antiice-this is said to be avoided by the QRH (might cause the other bleed to fail)
The reason is to have pressure in the ram on both 'sides' ,thus being able to pressurize both hyd sys,water sys..
And you won't have at any time two pack's on one source,due to the qrh instructions to close affected pack.
FC,LEM I hope this helps..
Brgds Alex
Last edited by alexban; 10th Feb 2005 at 09:46.