thank you very much with your explanationis the neumatic system need for the engines just for the start?if, when the engines running in ground i put off the apu bleed air and both engines bleed air switches, the engines are runningthis means, that the neumatic system is use only for the start of the engines? and of course trhe presurization?

"this means, that the neumatic system is use only for the start of the engines? and of course trhe presurization?"I think you just answered your own question... Without the pneumatic system switched on, the passengers would die :(Pneumatics are also used for:AirconditioningEngine inlet cowl anti-icingWing leading edge anti-icingPassenger drinking water tank pressurisationHydraulic reservoir pressurizationTAT probe operation on the ground (in some cases)Cargo Heating...and a few other things I probably haven't thought ofI repeat.. you DON'T need to switch off engine bleed for engine start. Just the airconditioning packs.Cheers.Q> イアン