SYDNEY - Australian authorities searching for a missing Malaysia Airlines passenger jet said on Monday they had lost a deep-water sonar detector being used to scour a patch of the ocean floor where the plane is believed to have gone down almost two years ago. Malaysia Airlines Flight MH370 disappeared with 239 people on board during a flight from Kuala Lumpur to Beijing in March 2014, sparking one of the greatest mysteries in aviation history. On Saturday, a piece of suspected plane wreckage was found off the east coast of southern Thailand but aviation experts and Thai officials said it was unlikely to belong to MH370. A piece of the plane washed up on the French island of Reunion in the Indian Ocean in July 2015 but no further trace has been found.