The simplest way to reduce the flow of air into the aircraft I work on, would be to turn off the recirculation fans in flight . . . This would save fuel but is a non standard way of operating the aeroplane. Engineering would not be allowed to modify the flow controls valves purely to save money - this would not happen where I work and I would not want to be a party to it either. One of the big benefits in recent times to reduce maintenance costs and increase comfort levels has been the introduction of a total ban on smoking acroos the board.