PERTH - The logging of a fifth signal spurred Friday's hunt for missing Malaysian airliner MH370 as search crews work round-the-clock to find elusive wreckage in the southern Indian Ocean.
The Australian-led operation out of a Perth airbase is racing to gather as many signals as possible to determine an exact resting place for the Boeing 777 before sending down a submersible to plumb the depths.
The ping-emitting beacons on Flight MH370's data and cockpit voice recorders are expected to fade, more than a month after the plane vanished with 239 people on board.
With analysis of the latest ping underway, the Perth-based Joint Agency Coordination Centre (JACC) said on Friday the search area had been further reduced to two zones totalling 46,713 sq km. The core of the search is now 2,312km north-west of Perth.
An Australian air force P-3C Orion surveillance plane, which had been dropping dozens of sonar buoys into the remote waters of the search zone, captured the new signal on Thursday afternoon.
"The acoustic data will require further analysis overnight but shows potential of being from a made-made source," JACC chief Angus Houston said in a statement late on Thursday.
The Orion was flying close to the area where two signals were detected at the weekend and two more on Tuesday by Australian navy ship Ocean Shield.
The vessel is dragging a US Navy "towed pinger locator" to listen for emissions from the black boxes.
Friday's weather forecast in the search zone was for 10-15 knot southerly winds with isolated showers, seas swells of 1m to 1.5m and visibility of 5km during the showers.
US Seventh fleet spokesman Commander William Marks had earlier voiced optimism that the first two sets of signals showed the hunt was getting "closer and closer".
"When you put those two (sets of pings) together, it makes us very optimistic," Cmdr Marks told CNN on Thursday.