Air Traffic Control and the Jet Aeroplane

Abstract

The fact that the de Havilland Comet cruises at nearly double the flying speed and nearly double the flight altitude of comparable piston-engined airliners is a measure of the great leap forward in air transport which the introduction of gas-turbine engines has brought about. It also illustrates an inherent feature of jet aircraft, for only at high speed and high altitude do turbo-jet engines, and to a less critical extent turbo-prop engines, operate at their maximum efficiency, expressed in distance flown per gallon of fuel consumed. With reduction of altitude and speed, however, the fuel consumption does not fall off proportionately and efficiency decreases rapidly. For example, even when taxying on the ground the Comet's fuel consumption is about 70 per cent of that at cruising altitude, and when flying at sea level the still-air distance flown on a given quantity of fuel is less than half of that at cruising altitude. In other words you get the best out of a jet aircraft when you are going somewhere fast, and when the length of the flight is sufficient for the aircraft to climb to its optimum cruising altitude and remain there for a considerable proportion of the flight time.

A Variable Fuel Reserve Policy

“…Whilst basically the method will apply to our turbo-prop operations, for which it was primarily developed, adjustments and improvements are necessary to meet the greater demands of high-altitude, high-fuel-consumption aircraft. 2 In particular, development is necessary in the field of operational control, such as in the flight planning and refuelling stage. To obtain the full benefits of this scheme it is necessary for a detailed survey of weather conditions along the route and in the terminal area to be undertaken by the captain before commencing his flight planning for the next stage.…”