KUALA LUMPUR - Investigations into the mystery of the missing Malaysian jet appeared to be at a deadlock on Wednesday, with an exhaustive background search of the passengers and crew showing nothing untoward and no sign that the plane could be quickly found.Eleven days have passed since Malaysia Airlines Flight MH370 went missing, and 26 nations are struggling to search for the airliner over an area roughly the size of Australia, or more than two-thirds the size of the United States.Malaysia's top official in charge of the unprecedented operation said it was vital to reduce the scale of the task and renewed appeals for sensitive military data from its neighbours that Malaysia believes may shed light on the airliner's fate."All the efforts must be used to actually narrow the corridors that we have announced - I think that is the best approach to do it. Otherwise we are in the realm of speculation again," Malaysia's Acting Transport Minister Hishammuddin Hussein told reporters late on Tuesday.The US Navy said it had switched mainly to using P-8A Poseidon and P-3 Orion aircraft instead ships and helicopters."The maritime patrol aircraft are much more suited for this type of operation since the search field is growing," said Navy Lieutenant David Levy, who is on board the USS Blue Ridge, the U.S. Navy ship that is coordinating the search effort."It's just a much more efficient way to search," he said.