THE WORLD'S BIGGEST PASSENGER AIRLINER LANDED FOR THE FIRST TIME AT EUROPE'S BUSIEST AIRPORT THURSDAY, FOR TESTS TO SEE IF LONDON HEATHROW IS READY FOR THE AIRBUS A380, ACCORDING TO AP. «IT IS CLEARLY QUITE A MOMENTOUS DAY IN U.K. AVIATION HISTORY,» BAA HEATHROW MANAGING DIRECTOR TONY DOUGLAS SAID JUST BEFORE THE PLANE LANDED EN ROUTE FROM THE BERLIN AIR SHOW.