Thank you for the explanations -in laymans terms for me I translate this to a car aircon, having it running impairs performance due to load.
I did find when researching the following on the boeing site (
Boeing: Commercial Airplanes - Cabin Air Quality - Myths and Facts) it says that turning one of the packs off saves little fuel as the other(s) compensate which if I understand correctly the fuel save option was removed on the 744 - I am guessing for the performance all packs must be switched off.
A very interesting and enlightening discussion, as slf - I normally consider we just roll and take off at max thrust and have not paid appreciation to the calculations you guys must make up front to make us do so safely. The more I read - the more I appreciate how complex your jobs are..
cheers