Australian investigators Saturday began examining a stricken Qantas jumbo jet that made a harrowing emergency landing in the Philippines with a giant hole in its fuselage. The Boeing 747-400 was cruising at 8,800 meters on Friday with 346 passengers aboard when it was shaken by what passengers described as an explosion. Oxygen masks dropped from the ceiling as the plane descended rapidly and debris flew through the cabin from a hole that suddenly appeared in the floor. En route to Melbourne, Australia from London, the plane managed to land safely minutes later at the Manila airport. There were no injuries among the passengers and crew. Four specialists from the Australian Transport Safety Bureau were inspecting the aircraft Saturday to determine what caused the damage, said Ruben Ciron, chief of the Civil Aviation Authority of the Philippines.