The integration of a system—or a group of systems — into a modern fixed-wing aircraft can only be satisfactorily achieved if the fuel penalty incurred by the aircraft is minimised, i.e. if the amount of fuel needed to restore the initial aircraft performance is kept to a minimum.

Over the years, aircraft systems have had to meet more and more stringent requirements which reflect not only on the increasing performance of aircraft, but also on the greater demands made by systems on the aircraft, a somewhat extreme example being that of the Mach 2 + Rockwell International B-l bomber on which the cooling requirements for the avionic equipment were to exceed several hundred kilowatts.

As such trends are likely to continue in the foreseeable future, the current deteriorating situation regarding fuel supplies and the ever rising costs involved, stresses the need for ensuring that systems on the next generation aircraft are designed for the least penalty and most efficient use of the available fuel.