Malaysian Airlines Flight MH370 vanished from civilian radar screens less than an hour after taking off from Kuala Lumpur with 239 people on board on a flight to Beijing on March 8.
The so-called Towed Pinger Locator will be crucial in finding the black box of the missing jetliner if a debris field is established by an Australian-led international search team scouring an area in the southern Indian Ocean some 2,500 km (1,550 miles) southwest of Perth.
Read: 'Pingers on missing Malaysian jet to stop emitting by Apr 6'
Chinese plane finds 'suspicious objects'
Australia still analysing French images
Australian Navy's HMAS Success, seen from the widow of a Royal Australian Air Force AP-3C Orion, searches for missing Malaysia Airlines flight MH370 in the southern Indian Ocean, Australia. AP
"If debris is found we will be able to respond as quickly as possible since the battery life of the black box's pinger is limited," Commander Chris Budde, US Seventh Fleet Operations Officer, said in an emailed statement.
Attention and resources in the search for the Boeing 777 have shifted in recent days from an initial focus north of the equator to an increasingly narrowed stretch of icy sea in the southern Indian Ocean.
Chinese and Japanese military aircraft were joining a 10-strong international fleet of planes scouring the area for the first time on Monday.
A flotilla of Chinese ships, including the icebreaker Xuelong, or Snow Dragon, is also making its way south.
Budde stressed that bringing in the black box detector, which is towed behind a vessel at slow speeds and can pick up "pings" from a black box to a maximum depth of 20,000 feet, was a precautionary measure.
Similarly, Australian Deputy Prime Minister Warren Truss stressed the challenges of the search.
"It's a lot of water to look for just perhaps a tiny object," Truss told Australian Broadcasting Corp. Radio. "Today we expect the weather to deteriorate and the forecast ahead is not that good, so it's going to be a challenge, but we will stick at it," he said.
Two Chinese military Ilyushin IL-76 aircraft, two Australian P3 Orions and two ultra-long range civilian jets were in the early search party on Monday. Another ultra-long range jet, a US Navy P8 Poseidon and two Japanese P3 Orions were due to depart later in the day.
A Chinese Ilyushin IL-76s aircraft sit on the tarmac at RAAF Pearce base ready to join the search for the missing Malaysia Airlines flight MH370 in Perth, Australia, Sunday. AP
A Royal Australian Air Force AP-3C Orion takes off at RAAF Pearce Base to join the search for the missing Malaysia Airlines flight MH370 in Perth. AFP
Read: Indian aircraft join search operations for missing plane
Australia was analysing French radar images showing potential floating debris that were taken some 850 kms (530 miles) north of the current search area. "We only recently got this information and we are still examining it," an AMSA spokeswoman told Reuters by telephone.
Malaysia said it received the images on Sunday and passed them on to Australia. "We are taking it into account but at this stage we are still focused on the same search area," the spokeswoman said, contradicting earlier comments from Australian Deputy Prime Minister Warren Truss that the search area had been expanded north to take into account the French sighting.
Australia has used a US satellite image of two floating objects to frame its search area.
The search planes are zeroing in on the areas around where the earlier sightings were made in an effort to find the object identified by China and other small debris, including a wooden pallet, spotted by a search plane on Saturday.
China said the object it had seen on the satellite image was 22 metres long (74ft) and 13 metres (43ft) wide.
Chinese Satellite image
A Chinese satellite image of an object spotted in the southern Indian Ocean that could be wreckage from missing Malaysian Airlines flight MH370. (Reuters)
It could not be determined easily from the blurred images whether the objects were the same as those detected by Australia, but the Chinese photograph could depict a cluster of smaller objects, said a senior military officer from one of the 26 nations involved in the search.
The wing of a Boeing 777-200ER is approximately 27 metres long and 14 metres wide at its base, according to estimates derived from publicly available scale drawings. Its fuselage is 63.7 metres long by 6.2 metres wide.Read: Dimensions of missing Malaysian jet MH370
NASA said it would use high-resolution cameras aboard satellites and the International Space Station to look for possible crash sites in the Indian Ocean. The US space agency is also examining archived images collected by instruments on its Terra and Aqua environmental satellites, said NASA spokesman Allard Beutel.
"Our satellites and space-based cameras are designed for long-term scientific data gathering and Earth observation. They're really not meant to look for a missing aircraft, and obviously NASA isn't a lead agency in this effort. But we're trying to support the search, if possible," Beutel said.
Truss said the aircraft flying on Monday would be focused on searching by sight, rather than radar, which can be tricky to use because of the high seas and wind in the area. Civilian aircraft, which can carry more people, have joined the search.
HIJACK OR SABOTAGE?
Investigators believe someone on the flight shut off the plane's communications systems. Partial military radar tracking showed it turning west and re-crossing the Malay Peninsula, apparently under the control of a skilled pilot.
That has led them to focus on hijacking or sabotage, but investigators have not ruled out technical problems. Faint electronic "pings" detected by a commercial satellite suggested it flew for another six hours or so, but could do no better than place its final signal on one of two vast arcs north and south.
The lack of solid news has meant a prolonged and harrowing wait for families of the passengers, who have complained in both Beijing and Kuala Lumpur about the absence of information.
A Malaysian statement said a "high-level" team briefed relatives in Beijing on Sunday in a meeting that lasted more than six hours.
While the southern arc is now the main focus of the search, Malaysia says efforts will continue in both corridors until confirmed debris are found.
"We still don't even know for certain if the aircraft is in this area," Truss said of the southern Indian Ocean search. "We're just clutching at whatever little piece of information that comes along to try to find the place we can concentrate the efforts."