Monkee - You are correct, as an example I believe the B777 MEL states that you may operate the aircraft with 4 of the 4 recirc. fans inoperative. The fuel increase is in the order of 0.3% for each of the 4 fans. Perhaps one could go all the way back to basics and ask why we have these fans in the first place ?. I read an interesting article last year from a source in Germany about the " pax fainting problem " on the B777 that put forward a theory that from their research, all those affected were seated next to the fuselage and behind the engine exhaust area and all were on RR Trent powered aircraft. It was thought that there was some kind of harmonic reasonance from the exhaust of the engines being transmitted through the fuselage skin and onto the unwary passengers, as Mutt stated, usually the young and the old. Nothing more was heard from this and our local RR men could not comment.