_h353_w628_m6_otrue_lfalseOfficials investigating the disappearance of a Malaysian airliner with 239 people on board are narrowing the focus of their inquiries on the possibility that it disintegrated in mid-flight, a senior source said on Sunday. Malaysia Airlines flight 370 vanished after climbing to a cruising altitude of 35,000 feet between Kuala Lumpur and Beijing in the early hours of Saturday, but search teams have still not been able to make any confirmed discovery of wreckage in seas beneath the plane’s flight path almost 48 hours after it took off. “The fact that we are unable to find any debris so far appears to indicate that the aircraft is likely to have disintegrated at around 35,000 feet,” said the source, who is involved in the investigations in Malaysia. MORE