The search for flight MH370

The hunt for Malaysia Airlines flight MH370 is continuing north west of Perth, Australia, with search teams using specialist equipment to survey the sea floor.

However, hopes that acoustic signals thought to be from the aircraft's "black box" flight recorders would lead them to the jet's final resting place have been dashed. Australian officials say a Bluefin-21 submersible robot has found nothing in its search of the area where four "pings" were detected in April.

Further specialist search equipment is now being sourced for wider underwater searches.

Ocean floor
Where is the search?

Since the plane disappeared on 8 March, the hunt has changed in scope many times.

At its largest, it covered 7.68 million sq km (2.96 million sq miles) - a total of 2.24 million square nautical miles. This was the equivalent of 11% of the Indian Ocean and 1.5% of the surface of the Earth.

However, from 16 March, satellite images of possible debris and tracking data released by the Malaysian authorities appeared to confirm that the plane crashed in the Indian Ocean, south west of Australia.

After searching an area more than 2,000km (1,240 miles) south-west of Perth, the hunt switched more than 1,000km (600 miles) further north, based on further analysis of radar data which showed the plane was going faster, thus using fuel more quickly.

Map showing the last-known movements of flight MH370

The search zone narrowed again in early April to an area of 850 sq km (328 sq miles) of the ocean floor - located close to acoustic signals detected by Australian teams.

The Australian vessel the Ocean Shield picked up four acoustic signals in the same broad area - on the 5 and 6 April and again twice on 8 April. Chinese ship Hai Xun 01 also registered a signal on 5 April, but this was 600km further south.

Then, at the end of May, the search zone was again extended to an area of 60,000 sq km (23,000 sq miles).

This extended area's sea bed is currently being mapped by the Chinese survey ship Zhu Kezhen, ready for a commercial operator to take over the search mission in August. The mission is expected to take up to a year, at an estimated cost of $55m (£33m) or more.

Authorities have also asked the UN's Comprehensive Nuclear Test Ban Treaty Organization to check its system of hydrophones, which are designed to pick up possible nuclear tests, for any clues as to where the aircraft may have crashed.

So far not one piece of debris has been identified or recovered.

Richard Westcott reports on the use of a pinger locator to find a black box

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Who has been taking part in the search?

Eight countries have been assisting - Australia, China, Japan, Malaysia, New Zealand, South Korea, the United Kingdom and the United States.

However, the investigation is being led by the Malaysian authorities, who are also liaising with the FBI, Interpol and other international law enforcement agencies.

Australia has been overseeing day-to-day search operations from its newly-created Joint Agency Co-ordination Centre (Jacc) based in Perth.

Members of China's Civil Aviation Administration and officials from the France's Office of Investigations and Analysis for the Safety of Civil Aviation have also been involved in the investigation.

The French are lending expertise from the two-year search for the flight recorders from the Air France Airbus A330 which crashed into the Atlantic Ocean in 2009.

British company Inmarsat, along with the UK Air Accident Investigations Branch, have provided detailed satellite data analysis to aid the hunt.

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What key equipment has been used?

Two vessels - the Australian naval support ship Ocean Shield and the UK's HMS Echo - used specialist listening equipment that can detect ultrasonic "pings" from the plane's "black box" flight recorders.

Graphic: Black Boxes

The Ocean Shield used a "towed pinger locator" (TPL), which is pulled underwater behind the ship at slow speeds and uses a highly sensitive listening device called a hydrophone to pick up signals.

Towed pinger locator

Once the "pings" were detected, the autonomous mini-submarine Bluefin-21 was despatched to create a detailed sonar map of the sea bed. It is also able to carry a camera unit to take pictures of any possible wreckage.

By 29 May, it had scoured 850 sq km (328 sq miles) of the ocean floor, Australia's Joint Agency Co-ordination Centre said.

The depth of the water in the search area is estimated to be between 2,000m and 4,000m (6,560ft and 13,120ft).

Bluefin-21

Early in the search, military aircraft also scoured the area for any possible floating debris.

Aircraft types involved in the search include a US Navy P-8 Poseidon and Australian, New Zealand, South Korean and Japanese P-3 Orion maritime surveillance planes.

Two Chinese Ilyushin Il-76s also operated out of RAAF Pearce air base near Perth, while Malaysia sent two C-130 Hercules aircraft.

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Lockheed Martin P3 Orion
  1. The Lockheed Martin P-3 Orion is equipped with radar and infrared sensors as well as observation posts to help detect any debris on the surface of the ocean. It also has three cameras beneath the landing gear capable of zooming in for a closer look.
  2. The four-engine turboprop plane is designed to fly low and slow to aid surveillance. Once it has reached the search location, one or two outer engines can be turned off to preserve fuel and extend the surveillance time.
  3. The plane is also fitted with a magnetic anomaly detector (MAD) - used for detecting submarines underwater. The aircraft also has acoustic detectors, which are able to detect sound 1,000ft (304.8m) below the surface of the ocean.
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Australia's HMAS Success, a naval oil tanker, is equipped with a crane which could be used to recover any possible wreckage.

China has deployed a number of vessels, among them the survey ship Zhu Kezhen, - or mapping of the ocean floor - in the area where the plane is thought to have crashed. This will take three months.

Its operations are being supported by the Chinese ship Haixun 01 and Malaysian vessel Bunga Mas 6, which are helping transport data to Fremantle each week for further processing. A contracted survey vessel will join the Zhu Kezhen in June.

The UK's HMS Tireless submarine, described as having "advanced underwater search capability", also joined the team.

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