Originally Posted by
FlightDetent
E.P.: I don't get any measurable extra fuel burn from HI as I like to re-select NORM when passing FL100. What's your procedure?
Cabin and cockpit temps can get quite high at one particular station where the external A/C is not that great and OAT is around 30 - 33°C, we select packs off for takeoff too. I usually set pack flow to HI once engines are started and leave it there until cabin temps reach at least 26°C. That could be anywhere between FL260 or so, all the way to TOC and even some time after reaching cruise altitude, depending on how good the A/C is on that particular aircraft. On the "worst" performing A/C I think I've seen a +100 kg fuel burn, but I haven't done enough measurements to guarantee such a number haha