UNITED States aircraft manufacturer Boeing said yesterday it was investigating two serious accidents involving its new 747-400 aircraft in the past seven weeks. On September 13, an Air France 747-400 jet overran the runway at Faaa airport in Tahiti with 270 people on board. It landed in a lagoon, and although no one was seriously injured, the airport was closed for a day. ''That was the first serious incident involving a 747-400 since we introduced the aircraft in 1989, and we have a team out there right now investigating what happened,'' said Chris Villiers, spokesman for Boeing at the company headquarters in Seattle. ''Since 1989 there have been no fatal accidents, or any accidents that have resulted in the loss of the airplane, for any of our aircraft,'' Mr Villiers said. ''To put it in perspective, our 747 fleet has flown about 2.8 billion kilometres since 1970, carrying about 1.4 billion passengers; in that time there have been 14 or 15 major accidents worldwide. Our safety record has been exemplary,'' he said. He did not believe the Tahiti and Kai Tak accidents were connected with any aircraft malfunction ''but, of course, we shall be making a full inquiry into what happened on both occasions''. He explained that international airline regulations stipulated that the Boeing 747-400, like all other aircraft, should be designed to land and float on water for enough time to allow all passengers, whether injured or not, to evacuate the aircraft and get away from the area in the lifeboats fitted at the end of all emergency chutes. Another spokesman said: ''It is like a tube of air: it is airtight and watertight, with the doors above water and a hold full of air, so it is bound to float.'' He said Boeing had a rigorous testing procedure to make sure all aircraft designs could stay afloat. The airplane involved in yesterday's accident was delivered to China Airlines in June this year. It was the 977th Boeing 747 off the production line. Salvage experts stood by throughout yesterday waiting to start the process of recovering the aircraft from the harbour. The territory's largest salvage firm, Hong Kong Salvage and Towage Co, was ready to divert a huge floating crane capable of lifting the aircraft in one piece. But last night the plane was still half submerged next to the runway. A decision on how to salvage it is expected to be made this morning. Salvage company deputy general manager Phileas Fong Yuk-choi said it would take 24 hours to redeploy the crane from maintenance work in north Lantau.