A pneumatic braking system has indisputable advantages over a hydraulic braking system for large and heavy aircraft in terms of braking force and secondary perhaps in terms of weight (pipes and hydraulic fluid). However it requires engine input to compress the air and generate the pressure and force required for braking, all of which use fuel.
What is the cost of a pneumatic braking system from a fuel point of view as opposed to hydraulic in relation to weight for a large Jumbo like the Airbus A380 or Boeing 747 if one had to consider using hydraulic brakes for any of these aircraft?