PERTH, Australia (AP) — An Australian aircraft Thursday detected  the fifth signal coming from a man-made device deep in the Indian Ocean, hopes that searchers will soon get the object's location and send down a robot  to confirm if it is a black box from the missing Malaysian jet.

The Australian air force P-3 Orion got the signal.

If confirmed, the signal would further narrow the help for Malaysia Airlines Flight 370 to search which was vanished on March 8  with 239 people aboard.

The Australian ship Ocean Shield picked up two underwater sounds on Tuesday, and two sounds it detected Saturday were determined to be consistent with the pings emitted from a plane's flight recorders, or "black boxes."

The Australian air force has been dropping sonar buoys to maximize the sound-detectors operating in a search zone that is now the size of the city of Los Angeles.

By Australian Navy each buoy is dangling a hydrophone listening device about 300 meters (1,000 feet) below the surface. The underwater search zone is currently a 1,300-square-kilometer (500-square-mile) 

Separately, a Malaysian government official said that investigators have concluded the pilot spoke the last words to air traffic control, "Good night, Malaysian three-seven-zero," and that his voice had no signs of duress. A re-examination of the last communication from the cockpit was initiated after authorities last week reversed their initial statement that the co-pilot was speaking different words.

The search for the black boxes is increasingly urgent.