Berlin  - Aircraft manufacturers at the Berlin Air Show forecast at a conference Wednesday rising demand over the next 20 years for cargo planes as world trade continues to grow.

Airbus chief executive Thomas Enders said 1,700 air-freight aircraft were currently flying the world's skies, but in two decades the number would more than double to 4,200.

He was speaking at the European Congress on Air Transport, an event during this week's air show, known by its German initials as the ILA, at Schoenefeld international airport south-east of Berlin.

Part of the demand would be met by removing seats from second-hand passenger jets and fitting them with rear doors. But Enders' sales forecast included about 900 brand-new air-freighters.

Statistics at the event showed international air cargo tonnages growing 5 per cent annually in recent years and analysts said the rate would accelerate to 6 per cent annually in the next few years.

Peter Hintze, the German government's coordinator of aviation policy, appealed to the aerospace industry to pay more attention to criticisms of the planes' pollution and climate-change impact.

He said the extensive use of older jets for air cargo meant greater public sensitivity about the freight business. Older planes are generally noisier and use more fuel per ton carried than new ones. (dpa)