HONG Kong's aviation buffs and environmentalists were in a flap - the Anglo-French supersonic airliner Concorde was coming. The aircraft touched down at 3.51pm at Kai Tak Airport on November 6, 1976, a day ahead of schedule. It was not its supersonic speed that accounted for Concorde's early arrival but Imelda Marcos, the wife of the president of the Philippines. The aircraft was on a sales promotion tour of the Far East when the First Lady hijacked it for a side trip to Hong Kong. She only stayed for three hours. The newspapers suggested rather unkindly that Mrs Marcos had come to Hong Kong on a ''shopping spree''. This dastardly allegation was absolutely untrue. Mrs Marcos had come to Hong Kong for lunch. Her party was driven directly from Kai Tak to the Peninsula Hotel where a magnificent banquet awaited them in the Marco Polo Suite. While Imelda and her cronies were filling up on champagne and caviar, the 16 members of Concorde's international aircrew were stuck at Kai Tak. The swiftness with which the First Lady had commandeered Concorde had taken the crew by surprise. They had left their passports behind in Manila and Hong Kong's friendly Immigration officials had refused to allow them to leave the airport. At 7.18pm, Concorde, with a well-fed First Lady aboard, flew back to Manila. It returned to Hong Kong the next day on its official visit. In spite of the heroic efforts of the French Aerospatiale Company and the British Aircraft Corporation's sales team, Philippine Airlines did not buy a single Concorde aircraft. The environmentalists were also disappointed. Their gloomy predictions that the noise level would prove a health hazard to anyone living on the shores of Kai Tak Nullah turned out to be completely unfounded. The Concorde was only slightly noisier than a Boeing 707 aircraft.