Airbus Industries provides forecasts of revenue ton-kilometers and freighter aircraft. According to these forecasts, the ratio of revenue ton kilometers per all-cargo aircraft will continue to increase. The forecast takes into account both changes in average aircraft size and shifts in cargo tonnage between all-cargo aircraft and mixed-use aircraft. It can be assumed that the ratio of tonnage per all-cargo aircraft departures would increase at the same rate as the ratio of revenue ton kilometers per all-cargo aircraft. All-cargo aircraft departures can then be derived from the forecast of air cargo tonnage. It should also be noted that Airbus and Boeing are in business to sell aircraft.