Could I ask any engineers out there another question.
I like individual overhead air jets. The cabin can then be on the warm side, but if the jet is cool the desired temperature can be maintained by adjusting the strength of the air jet. Unfortunately many aircraft such as BA LH no longer have individual jets. Presumably the reason for this is economic - we all know about airlines cutting requesting pilots to turn off packs to save fuel.
My question is: how much fuel is actually saved by not having individual air jets. Studies must have been done. Is it significant?
Another, related, question comes to mind. The rear of a 747 is always stuffy on the ground, prior to start up, even with the APU on. If the APU is unservicable conditions are generally very uncomfortable even when it is not too warm outside. Presumably this is due to the limited capacity of the APU and the way that air is distributed along the cabin. I have found that when there is an a ground pre-conditioned air supply - almost universal in the USA, also at LHR T5 - conditions are much more comfortable. Presumably this supply is more powerful than that from the APU?