When Viscount 720 aircraft were delivered to Trans-Australia Airlines it became clear that increased attention would have to be given to performance analysis and the preparation of flight planning data.

Previous operational experience had been restricted to piston-engined aircraft which, for flight planning purposes, could be regarded as cruising at a certain air speed and burning fuel at a certain rate. Temperature effects were negligible because it was the accepted practice to restore power on hot days by slightly increasing boost settings. Altitude effects, although not truly negligible, were certainly small and could be covered by using flight planning figures from the conservative side of the range. With the Viscount, however, the specific range at cruising altitude was found to be almost twice its sea level value and a 10°C. rise in temperature was capable of reducing true air speed by 20 knots.