WATCHING the huge Airbus 380 land at Heathrow airport yesterday and make its lumbering way to the terminal I was reminded for a moment of another giant aircraft, the Bristol Brabazon which in the late 1940s was both the largest aircraft in the world and the Biggest White Elephant. It was capable of flying non-stop betwen London and New York but when stress marks were discovered in the propellor mountings the British government took the opportunity of cancelling the expensive project. Things are better managed nowadays with European co-operation and yesterday's demonstration landing of the A380 will have given confidence both to its manufacturers and the 16 airlines which have placed 159 firm orders for the plane, first among them Singapore Airlines which plans the first service beween Sydney, Singapore and London at the end of this year. The only sour note comes from Seattle where the Boeing Company continues to make threatening noises about alleged government subsidies being paid to get the A380 project off the ground. Some travellers will have mixed feelings about sharing space with 500 other passengers. Environmentalists will say that aircraft, even one as efficient and clean as the A 380, are among the worst polluters and that measures should be taken to reduce air travel. But how? Since most pollution is caused on take off and landing it makes sense to carry as many people as possible each time.