Search for Malaysia Airlines Flight 370

An Australian AP-3C Orion flies over the British survey ship HMS Echo on 12 April 2014.

The search for Malaysia Airlines Flight 370 began on Saturday, 8 March 2014. Malaysia Airlines Flight 370 was a scheduled international passenger flight that disappeared while flying from Kuala Lumpur International Airport to Beijing Capital International Airport. Analysis of communications between the aircraft and Inmarsat by multiple agencies has concluded that the flight ended in the southern Indian Ocean.

A multinational search effort became the largest and most expensive in history. An analysis of possible flight paths was conducted, identifying a 60,000 km² (23,000 sq mi) primary search area, approximately 2,000 km (1,200 mi) west of Perth, Western Australia, which takes six days for vessels to reach from Fremantle harbour, near Perth. The underwater search of this area began on 5 October 2014 at a cost of A$60 million (approximately US$56 million or €41 million). As of 5 March 2015, over 26,000 square kilometres (10,000 sq mi) of seafloor has been searched, which is over 40% of the priority search area; with no significant delays, the search of the priority search area will be completed around May 2015. On 29 July 2015, a piece of marine debris, later confirmed to be a flaperon from Flight 370, was found on Réunion Island.

Ships and aircraft from Australia, China, Japan, Malaysia, New Zealand, South Korea, the United Kingdom and the United States were involved in the search of the southern Indian Ocean. Satellite imagery was also made available by Tomnod to the general public so they could help with the search through crowdsourcing efforts.

Disappearance

Main article: Malaysia Airlines Flight 370 § Disappearance

Malaysia Airlines Flight 370 was a scheduled flight in the early morning hours of 8 March 2014 from Kuala Lumpur, Malaysia to Beijing, China. It was one of two daily flights operated by Malaysia Airlines from its hub at Kuala Lumpur International Airport (KLIA) to Beijing Capital International Airport—scheduled to depart at 00:35 local time (MYT; UTC+08:00) and arrive at 06:30 local time (CST; UTC+08:00). At 00:41 MYT, Flight 370 took off with 239 persons aboard—two pilots, ten cabin crew, and 227 passengers (152 of whom were Chinese citizens). Flight 370 was cleared by air traffic control to proceed on a direct path to waypoint IGARI (), located between Malaysia and Vietnam over the South China Sea (near the boundary with the Gulf of Thailand).

At 01:07 MYT, the aircraft was at flight level 350—approximately 35,000 feet (11,000 m) above sea level—when the final message using the ACARS protocol was sent from the aircraft. At 1:19 MYT, Lumpur area air traffic control (ATC) initiated a hand-off to Ho Chi Minh area ATC. The Captain responded "Good night Malaysian Three Seven Zero," after which no further communications were made with the pilots. The crew was expected to contact air traffic control in Ho Chi Minh City as the aircraft passed into Vietnamese airspace just north of the point where the final verbal communication was made. Less than two minutes later, at 01:21, the aircraft disappeared from the radar screens of both Malaysian and Vietnamese ATC, which use secondary radar to track aircraft. No distress call was made.

Flight 370 was expected to arrive in Beijing at 6:30 local time (same time zone as Malaysia; 22:30 UTC, 7 March). At 7:24, Malaysia Airlines issued a media statement that Flight 370 was missing after contact was lost with Malaysian ATC at 2:40. The time of the last contact with ATC was later corrected to 1:19; Malaysia Airlines was notified at 2:40.

Initial search in Southeast Asia (March 2014)

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The initial search area in Southeast Asia

The watch supervisor at Kuala Lumpur Area Control Centre—which was the air traffic control centre that was last in contact with Flight 370—activated the Kuala Lumpur Aeronautical Rescue Coordination Centre (ARCC) at 05:30, over four hours after communication was lost with Flight 370. When Malaysia Airlines issued a media statement two hours later, they claimed that they were "working with the authorities who have activated their Search and Rescue team to locate the aircraft".

On 9 March, the Chief General of the Royal Malaysian Air Force announced that Malaysia is analysing military radar recordings and that there is a "possibility" that Flight 370 turned around and travelled over the Andaman Sea. The search radius was increased from the original 20 nmi (37 km; 23 mi) from its last known position, south of Thổ Chu Island, to 100 nmi (190 km; 120 mi), and the area being examined then extended to the Strait of Malacca along the west coast of the Malay Peninsula, with waters both to the east of Malaysia in the Gulf of Thailand, and in the Strait of Malacca along Malaysia's west coast, being searched.

Numerous sightings of possible debris were made, but no debris from Flight 370 was discovered. Oil slicks detected off the coast of Vietnam on 9 and 10 March later tested negative for aviation fuel. Satellite images taken on 9 March and posted on a Chinese website showed three floating objects measuring up to 24 × 22 metres (79 × 72 ft) at , but a search of the area did not find the objects; Vietnamese officials said the area had been "searched thoroughly". By the end of 9 March, 40 aircraft and more than two dozen vessels from several nations were involved in the search.

The Royal Malaysian Air Force confirmed on 10 March that Flight 370 made a "turn back". The following day, China activated the International Charter Space and Major Disasters to aggregate satellite data to aid the search. On 12 March, Malaysian officials announce that an unidentified aircraft, possibly Flight 370, was last located by military radar at 2:15 in the Andaman Sea, 320 kilometres (200 mi) northwest of Penang Island and near the limits of the military radar's coverage. The focus of the search shifted to the Andaman Sea and the Malaysian government requested help from India to search in the area.

International involvement

The Malaysian government mobilised its civil aviation department, air force, navy, and Maritime Enforcement Agency; and requested international assistance under Five Power Defence Arrangements provisions and from neighbouring states. Various nations mounted a search and rescue mission in the region's waters. Within two days, the countries had already dispatched more than 34 aircraft and 40 ships to the area.

On 11 March, the China Meteorological Administration activated the International Charter on Space and Major Disasters, a 15-member organisation whose purpose is to "provide a unified system of space data acquisition and delivery to those affected by natural or man-made disasters", the first time the charitable and humanitarian redeployment of the assorted corporate, national space agency, and international satellite assets under its aegis had been used to search for an airliner.

Another 11 countries joined the search efforts by 17 March after more assistance was requested by Malaysia. At the peak of the search effort and before the search was moved to the south Indian Ocean, 26 countries were involved in the search, contributing in aggregate nearly 60 ships and 50 aircraft. In addition to the countries already named, these parties included Australia, Bangladesh, Brunei, Cambodia, China, France, India, Indonesia, Japan, Myanmar, New Zealand, Norway, Philippines, Russia, Singapore, South Korea, Taiwan, Thailand, United Arab Emirates, United Kingdom, United States, and Vietnam. While not participating in the search itself, Sri Lanka gave permission for search aircraft to use its airspace. Malaysia deployed military fixed-wing aircraft, helicopters, and ships. A co-ordination centre at the National Disaster Control Centre (NDCC) in Pulau Meranti, Cyberjaya, was established.

On 16 March, three staff members of the French government agency BEA flew to Kuala Lumpur to share with Malaysian authorities their experience in the organisation of undersea searches, acquired during the search for the wreckage of Air France Flight 447. The United Kingdom provided technical assistance and specialist capabilities from the Ministry of Defence, the UK Hydrographic Office, Department for Transport and the Met Office. The Comprehensive Nuclear-Test-Ban Treaty Organization Preparatory Commission analysed information from its network of infrasound detection stations, but failed to find any sounds made by Flight 370.

Satellite communications and radar

Further information: Analysis of Malaysia Airlines Flight 370 satellite communications

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The location of the aircraft at its final "handshake" at 8:10 was along this arc, calculated from the communications with the Inmarsat network. Malaysian officials released a modified version on 15 March that omitted the segment from Java to the Thailand-Laos border.

On 11 March, New Scientist reported that, prior to the aircraft's disappearance, two reports using the Aircraft Communications Addressing and Reporting System (ACARS) protocol had been automatically sent to engine manufacturer Rolls-Royce's monitoring centre in the United Kingdom; The Wall Street Journal, citing sources in the US government, asserted that Rolls-Royce had received an aircraft health report every thirty minutes for five hours, implying that the aircraft had remained aloft for four hours after its transponder went offline.

Also on 11 March, it was reported that military radar indicated the aircraft turned west away from the intended flight path and continued flying for 70 minutes before disappearing from Malaysian radar near Pulau Perak. It was also reported that it had been tracked flying at a lower altitude across Malaysia to the Malacca Strait, approximately 500 kilometres (310 mi) from its last contact with civilian radar. The next day, the Royal Malaysian Air Force chief denied the report.

A few hours later however, the Vietnamese transport minister claimed that Malaysia had been informed on 8 March by Vietnamese air traffic control personnel, that they had "noticed the flight turned back west". A U.S. radar expert analysing the radar data reported that they did indeed indicate that the aircraft had headed west across the Malay Peninsula. The New York Times reported that the aircraft experienced significant changes in altitude.

The following day, Hishammuddin Hussein, the acting Malaysian Minister of Transport, refuted the details of The Wall Street Journal report stating that the final engine transmission was received at 01:07 MYT, prior to the flight's disappearance from secondary radar. The WSJ later amended its report and stated simply that the belief of continued flight was "based on analysis of signals sent by the Boeing 777's satellite-communication link... the link operated in a kind of standby mode and sought to establish contact with a satellite or satellites. These transmissions did not include data."

Inmarsat said that "routine, automated signals were registered" on its network, and that analysis of "keep-alive message[s]" that continued to be sent after air traffic control first lost contact could help pinpoint the aircraft's location, which led The Independent to comment on 14 March that the aircraft could not have met with a sudden catastrophic event, or all signals would have stopped simultaneously.

Although Bloomberg News said that analysis of the last satellite "ping" received suggested a last known location approximately 1,000 miles (1,600 km) west of Perth, Western Australia, the Malaysian Prime Minister Najib Razak said on 15 March that the last signal, received at 08:11 Malaysian time, might have originated from as far north as Kazakhstan. Najib explained that the signals could not be more precisely located than to one of two possible loci: a northern locus stretching approximately from the border of Kazakhstan and Turkmenistan to northern Thailand, or a southern locus stretching from Indonesia to the southern Indian Ocean. Many of the countries on a possible northerly flight route – China, Thailand, Kazakhstan, Pakistan, and India – denied the aircraft could have entered their country's airspace, because military radar would have detected it.

Shift to the Southern Indian Ocean (March–May 2014)

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The shifting search zones for Flight 370 in the Southern Indian Ocean. The inset shows the path of taken by the vessel ADV Ocean Shield operating a towed pinger locator, acoustic detections, and the sonar search. The current underwater phase (both the wide area search and priority area) is shown in pink.

On 15 March, based on military radar data and transmissions between the aircraft and an Inmarsat satellite, investigators concluded that the aircraft had diverted from its intended course and headed west across the Malay Peninsula, then continued on a northern or southern track for around seven hours.

The focus of the search shifted to the southern part of the Indian Ocean, west of Australia. In the first two weeks of April, aircraft and ships deployed equipment to listen for signals from the underwater locator beacons attached to the aircraft's "black boxes". Four unconfirmed signals were detected between 6 and 8 April near the time the beacons' batteries were likely to have been exhausted. A robotic submarine searched the seabed near the detected pings until 28 May, with no debris being found.

Surface search

On 17 March, Australia agreed to lead the search in the southern locus from Sumatra to the southern Indian Ocean. The search would be coordinated by the Australian Maritime Safety Authority (AMSA), with an area of 600,000 km² (230,000 sq mi) between Australia and the Kerguelen Islands lying more than 3,000 kilometres (1,900 mi) Southwest of Perth, to be searched by ships and aircraft of Australia, New Zealand, and the United States. This area, which Australian PM Tony Abbott described as "as close to nowhere as it's possible to be", is renowned for its strong winds, inhospitable climate, hostile seas, and deep ocean floors. On 18 March, the search of the area began with a single Royal Australian Air Force P-3 Orion aircraft. On 19 March, the search capacity was ramped up to three aircraft and three merchant ships; the revised search area of 305,000 square kilometres (118,000 sq mi) was about 2,600 kilometres (1,600 mi) south-west of Perth.

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Crew members on board a P-8A Poseidon manning terminals while searching for surface debris and locator beacons from Flight 370 in the southern Indian Ocean.

Search efforts intensified on 20 March, after large pieces of possible debris had been photographed in this area four days earlier by a satellite. Australia, the United Kingdom, the United States, China, Japan, New Zealand, and South Korea assigned military and civilian ships and aircraft to the search. China published images from satellite Gaofen 1 on 22 March that showed large debris about 120 km (75 mi) south west of the previous sighting. The same day, HMAS Success became the first naval vessel to reach the search area. On 26 March, images from French satellites indicated 122 floating objects in the southern Indian Ocean. Thai satellite images published on 27 March showed about 300 floating objects about 200 km (120 mi) from the French satellites' target area. The abundant finds, none confirmed to be from the flight, brought the realisation of the prior lack of surveillance over the area, and the vast amounts of marine debris littering the oceans.

On 28 March, revised estimates of the radar track and the aircraft's remaining fuel led to a move of the search 1,100 kilometres (680 mi) north-east of the previous area, to a new search area of 319,000 square kilometres (123,000 sq mi), roughly 1,850 kilometres (1,150 mi) west of Perth. This search area had more hospitable weather conditions.

On 30 March, four large orange-coloured objects found by search aircraft, described by media as "the so far most promising lead", turned out to be fishing equipment. On 2 April, the centre of the search area was shifted again 456 kilometres (283 mi) east, to a position 1,504 kilometres (935 mi) west of Perth. The same day, Royal Navy survey vessel HMS Echo and submarine HMS Tireless arrived in the area, with HMS Echo starting immediately to search for the aircraft's underwater locator beacons (ULBs) fitted to the "black box" flight recorders, whose batteries were expected to expire around 7 April.

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By 28 April, the drifted search area (outlined in grey) was over 2,500 km (1,600 mi) wide. The dots indicate the probable locations of debris on 28 April, based on a splash point in zones A-B (outlined in blue).

The surface search ended on April 28. In a press conference, Australian Prime Minister Tony Abbott noted that any debris would likely have become waterlogged and sunk and that the aircraft involved in the surface search were "operating at close to the limit of sensible and safe operation". The surface search in Southeast Asia and the Indian Ocean lasted 52 days, during 41 of which Australia coordinated the search. Over 4,500,000 km² (1,700,000 sq mi) of ocean surface was searched. In the Southern Indian Ocean, 29 aircraft from seven countries conducted 334 search flights; 14 ships from several countries were also involved. Although the seafloor sonar survey will continue, Abbott says plans for the next phase of the search, which will involve commercial companies and use towed sonar to more easily scan large areas of seafloor, are being developed.

Underwater locator beacon search

On 4 April, the search was refocused to three more northerly areas from 1,060 to 2,100 kilometres (660 to 1,300 mi) west of Learmonth, spanning over 217,000 square kilometres (84,000 sq mi). ADV Ocean Shield, fitted with a TPL-25 towed pinger locator, together with HMS Echo – which carried a "similar device", began searching for pings along a 240-kilometre (150 mi) seabed line believed to be the Flight 370 impact area. Operators considered it a shot in the dark, when comparing the vast search area with the fact that TPL-25 could only search up to 130 square kilometres (50 sq mi) per day.

On China's announcement of two unconfirmed acoustic events picked up by Haixun 01 through a handheld hydrophone on 4 and 5 April, the Joint Agency Coordination Centre (JACC) ordered HMS Echo to the area, to attempt verification with more advanced equipment.

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Deployment of a towed pinger locator for detecting an aircraft's ULB.

On 6 April, JACC announced that Ocean Shield had also picked up a signal, about 300 nautical miles (560 km; 350 mi) from Haixun 01. It was announced the next day that the TPL-25 pinger locator towed by Ocean Shield had picked up a signal twice on 6 April. The first was on the morning of 6 April, at approximately 3,000 metres (9,800 ft) depth, and lasted two hours and 20 minutes. The second signal reception took place at approximately 300 metres (980 ft) depth and lasted 13 minutes. During the second episode, two distinct pinger returns were audible. Both episodes of recorded signals, which took place at roughly the same position though several kilometres apart, were considered to be consistent with signals expected from an aircraft's flight recorder ULB. The signals received by Ocean Shield were recorded at the north of a newly calculated impact area, which was announced on 7 April, while the Haixun 01 signals had been recorded at its southern edge. Ocean Shield detected two more signals on 8 April. The first was acquired at 16:27 AWST and held for 5 minutes, 32 seconds and the second was acquired at 22:17 AWST and held for around seven minutes. Experts had determined that the earlier signals captured by Ocean Shield were "very stable, distinct, and clear ... at 33.331 kHz and ... consistently pulsed at a 1.106-second interval". These were said to be consistent with the flight recorder ULB. but the frequency of the detections was well outside the manufacturer's specification of 37.5 +/- 1. The later signals were at a frequency of 27 kHz, which raised doubts that they were from a black box. On 10 April, a signal recorded by one of the sonobuoys deployed with a hydrophone at 300 metres depth was found unlikely to have originated from Flight 370.

Seafloor sonar survey

On 14 April, due to the likelihood of the ULBs' acoustic pulses having ceased because their batteries would have run down, the Towed Pinger Locator search gave way to a seabed search using side-scan sonar installed in a Bluefin-21 Autonomous Underwater Vehicle. The first day's search was aborted because the sea bed was considerably deeper than the maximum operating depth of Bluefin. Scanning subsequently resumed and after covering 42 square miles in its first four dives, the submersible was reprogrammed to allow it to dive 604 feet lower than its operational limit of 14,800 feet, when the risk of damage was assessed as "acceptable". By this time the search was believed to have cost $100 million (£72m) and had been labelled "the costliest in aviation history".

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Ocean Shield deploys Bluefin-21, 14 April 2014.

Bluefin-21 required 16 missions to complete its search of the 314 square kilometre area around the detections made by the Towed Pinger Locator. At a news conference in Canberra on 28 April, Tony Abbott said "It is now 52 days since Malaysia Airlines Fight MH370 disappeared and I'm here to inform you that the search will be entering a new phase". Abbott also explained that "a much larger" area of the ocean floor would then be searched; it was "highly unlikely" that any surface wreckage would be found; and that the aerial searches had been suspended. Mission 17 of Bluefin-21, covering the new, wider search area, was on 30 April.

During a tripartite meeting with officials from Australia, Malaysia, and China on 5 May, Australian Deputy Prime Minister Warren Truss announced that a "detailed oceanographic mapping of the search area" will be conducted to "be able to undertake [the next phase of the] search effectively and safely". It was necessary for planning the fifth phase of the search and because equipment used for the underwater search in this area would need to operate close to the seafloor (about 100 m). The bathymetric survey was made at a resolution of 100 metres (330 ft) per pixel, which is substantially higher than previous measurements of the seafloor in this area made by satellites (see image at right) and a few passing ships which had their sonar turned on.

On 12 May, it was reported that the captain of Ocean Shield said there was increasing doubt that pings No. 3 and No. 4 detected on 8 April originated with MH370's black boxes because their frequency of about 27 kHz was too far below the pinger's design frequency of 37.5 kHz. Pings No. 1 and No. 2, detected on 5 April at 33 kHz, were still being considered by the search authorities. On 13 May the search was interrupted due to problems with both the transponder mounted on Ocean Shield and that mounted on Bluefin-21. By 22 May those problems had been resolved and the search was resumed.

On 29 May, Truss announced that no aircraft debris had been found in the area searchers had previously reported "pings" from the black boxes. The announcement followed a statement by U.S. Navy's Deputy Director of Ocean Engineering that all four pings were no longer believed to have come from the aircraft's flight recorders. Truss informed parliament that, beginning in August, after a new commercial operator for the search effort had been selected, the search would move into a new phase "that could take twelve months". Equipment envisaged to be used would include towed side-scan sonar.

Bathymetric survey (May–December 2014)

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Data obtained from the baseline bathymetric survey (coloured) contrasted with previously-available satellite data (grey).

The Chinese survey vessel Zhu Kezhen departed Fremantle on 21 May to begin the bathymetric survey. On 10 June, the Australian Transport Safety Bureau (ATSB) signed a contract with the Dutch deep sea survey company Fugro to conduct a bathymetric survey of the seafloor in a new search area southwest of Australia. Fugro deployed their vessel MV Fugro Equator, which began bathymetric survey operations on 18 June. The Zhu Kezhen ended survey operations on 20 September and began its return passage to China. The bathymetric survey charted around 208,000 square kilometres (80,000 sq mi) of seafloor through 17 December, when it was suspended for Fugro Equator to be mobilised in the underwater search.

Underwater search (October 2014)

On 26 June, plans for the next phase of the search were formally announced; the search zone for the new phase is shifted to a new region of up to 60,000 square kilometres (23,000 sq mi) near Broken Ridge in the southern Indian Ocean based on a report by the ATSB. The search was expected to begin in August and after the bathymetric survey was complete, but it was delayed until October with only part of the survey completed.

Malaysia announced in July that they had contracted with state-run oil company Petronas to supply a team to participate in the search. Petronas, in turn, has contracted the vessel GO Phoenix—owned by Australian company GO Marine Group—and the marine exploration firm Phoenix International, who will supply experts and equipment. Phoenix recovered black boxes from several recent undersea aircraft wrecks: Air France Flight 447, Yemenia Flight 626, Adam Air Flight 574, and Tuninter Flight 1153. Phoenix planned to use the SLH ProSAS-60 towed synthetic aperture side scan sonar system (rated to 6,000 m depth) to produce a high-resolution image of the ocean floor. On 6 August, Australia, Malaysia, and China jointly announced that Fugro had been awarded a contract to conduct this latest phase of the search.

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Map of search operations for the underwater search which began in October 2014.

The underwater search began on 6 October with the vessel GO Phoenix, which departed Jakarta on 24 September and calibrated its instruments before arriving in the search zone on 5 October. Based on further analysis of Flight 370's satellite communications, the priority search area for the underwater search was shifted south from the area identified in June. On 18 October, Fugro Discovery departed Perth to join the search. The two vessels were joined by Fugro Equator and Fugro Supporter in January 2015.

On 16 April 2015, a tripartite meeting between Malaysian, Australian and Chinese officials was held. Over 60 percent of the 60,000 km² (23,000 sq mi) priority search area had been searched and, excluding significant delays, the search of the priority search area was expected to be mostly complete by the end of May. The countries agreed that if no trace of the aircraft is found in the priority search area, the underwater search would be extended to an additional 60,000 km² (23,000 sq mi) of adjacent seafloor. As of 29 July 2015, over 55,000 km² (21,000 sq mi) of seafloor has been searched during the underwater phase.

In early May, Fugro Supporter withdrew from the underwater search and offloaded its AUV in Fremantle. Sea conditions during the austral winter are too rough to safely launch and recover the AUV and therefore, AUV operations will be suspended during the winter months. However, the AUV will be kept ready to assist the search at short notice. On 20 June, GO Phoenix left the search area to begin passage to Singapore, where it will be demobilized from search activities.

Methodology

External images
A category 2 seafloor feature
A category 3 seafloor feature

Examination of possible end-of-flight scenarios indicate the aircraft may be located relatively close to the seventh BTO arc. On account of this, the underwater search began at the seventh BTO arc and has progressed outwards. Towed underwater vehicles equipped with synthetic aperture sonar, side scan sonar, and multi-beam echo sounders are towed close to the seafloor to create a three-dimensional picture of the seafloor topography. The imagery is analysed aboard the vessels; areas of interest, called "contact points", are classified into three levels:

• Category 3: Areas that stand out from their surroundings and are of some interest, but are unlikely to be significant to the search.
• Category 2: Areas of comparatively more interest, but still unlikely to be significant to the search. Some of these are possibly manmade objects, such as objects with the dimensions of shipping containers.
• Category 1: Areas of high interest to the search, requiring prompt investigation.

As of 5 March 2015, no seabed features have been classified as category 1, over ten features have been classified as category 2, and over 100 features classified as category 3.

Underwater search assets

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Fugro Discovery departing from Fremantle, February 2016

• MV Fugro Discovery – Originally carried an EdgeTech DT-1 towfish, named Dragon Prince, which was replaced with a new towfish, named Intrepid, in April 2015. The vessel joined the underwater search on 23 October 2014.
• MV Fugro Equator – Originally scheduled to join the search in late October, but resumed bathymetric survey work from 19 November to 17 December while waiting for equipment to arrive. It returned to Fremantle for mobilisation for the underwater search and joined the underwater search on 15 January 2015.
• MV Fugro Supporter – Participated in the search from late January until early May 2015.
• MV GO Phoenix – Carrying experts and equipment from Phoenix International. The first vessel to begin underwater search operations, on 6 October 2014. It left the search on 20 June 2015.

MV Fugro Discovery, MV Fugro Equator, and MV GO Phoenix are equipped with towed underwater vehicles (also known as "towfish"), which carry synthetic aperture sonar, side scan sonar, and multi-beam echo sounders. The towfish are towed behind the vessel on cables up to in length. The length of the cable is varied to keep the towfish at an altitude of 100–150 metres (330–490 ft) above the seafloor. The data collected by the instruments are relayed in real-time along the tow cable to the vessel, where it is processed and analysed to see if any debris associated with Flight 370 is present on the seafloor.

The MV Fugro Supporter is equipped with a Kongsberg HUGIN 4500 autonomous underwater vehicle (AUV), which carries the same instruments as the towfish deployed by the other vessels. Unlike the towfish, the AUV is self-propelled and can manoeuvre itself to maintain a constant altitude above the seafloor. When launched, the torpedo-shaped AUV dives to the proper altitude, then follows a pre-programmed search pattern for up to 24 hours, collecting sonar data for up to 24 hours; when the mission is complete, the AUV surfaces and is recovered by the vessel, where the data is downloaded and the batteries are swapped for the next mission. The AUV is used to scan areas which cannot be effectively searched by the towfish on the other three vessels. Because of the difficultly in operating the AUV during the austral winter months due to sea conditions, the AUV operations will be suspended during the austral winter months.

Shipwreck discovery

On 13 May 2015, it was announced that Fugro Equator had discovered wreckage of a previously uncharted 19th century cargo ship 4,000 metres underwater, more than 1,000 km off Australia's west coast. Fugro Supporter was diverted to the area to deploy an unmanned submarine to scan the seabed. Imaging of the site clearly showed an anchor and other manmade objects. It was announced that the related imagery would be provided to expert marine archaeologists for potential identification. Peter Foley, director of search operations, called it a "fascinating find but it's not what we're looking for".

Loss of towed sonar unit

In January 2016, a towed sonar vehicle collided with an underwater mud volcano despite its use of forward-looking obstacle avoidance sonar.

Debris discovered (July 2015)

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Debris location relative to the known flight path (red), calculated flight path (yellow), and underwater search area since October 2014 (dark blue; 46% searched as of 29 July 2015).

On 29 July 2015, airliner marine debris was found on the coast of Réunion Island in the western Indian Ocean, about 4,000 km (2,500 mi) west of the underwater search area and 5,600 km (3,500 mi) southwest of the aircraft's last primary radar contact. The object had a stenciled internal marking "657 BB". The following day, a damaged suitcase, which may be associated with Flight 370, was found. The location is consistent with models of debris dispersal 16 months after an origin in the current search area, off the coast of Australia. On 31 July, a Chinese water bottle and an Indonesian cleaning product were found in the same area; all such debris is receiving intense scrutiny.

Aviation experts have stated that the piece of debris resembles a wing flaperon from a Boeing 777, noting that the marking "657 BB" is a code for a portion of a right wing flaperon from that aircraft. The object was transported from Réunion—an overseas department of France—to Toulouse, for examination by France's civil aviation accident investigation agency, the Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile, and a French defence ministry laboratory. Malaysia is sending investigators to both Réunion and Toulouse. Furthermore, French police are conducting a search of the waters around Réunion for additional debris, and the Malaysian Transportation Minister, Liow Tiong Lai, asked countries near Réunion, including Mauritius, for assistance in the search for debris.

On 5 August, the Malaysian Prime Minister announced that experts have "conclusively confirmed" that the debris found on 29 July is from Flight 370; the debris is the first physical evidence that Flight 370 ended in the Indian Ocean. On 3 September French prosecutors formally announced that the flaperon was certainly from Flight 370, a unique serial number having been formally identified by a technician from Airbus Defense and Space in Spain, which had manufactured the flaperon for Boeing.

Search for additional debris

A week after the discovery of a flaperon from Flight 370 on a beach on Réunion (an overseas department of France), France announced plans for an aerial search for possible marine debris around the island. On 7 August 2015, France began searching an area 120 km (75 mi) by 40 km (25 mi) along the east coast of Reunion. Foot patrols for debris along beaches are also planned. Malaysia has asked authorities in neighboring states to be on alert for marine debris which could be from an aircraft.

On 23 March 2016, what appeared to be a piece of a Rolls Royce engine cowling was found on a beach in South Africa. The Malaysian authorities have sent a team to recover the piece and determine whether or not it came from the missing plane.

Analysis of hydroacoustic data

A source of evidence to assist in locating the final resting place of the aircraft is analysis of underwater sound recordings. If the aircraft hit the ocean hard, hydroacoustic recordings could have potentially recorded an impact event. Furthermore, the aircraft's flight data recorders were fitted with underwater 'pingers', which emit a detectable, pulsating acoustic signal that could have potentially led searchers to their locations.

Impact event

If Flight 370 had impacted the ocean hard, resulting underwater sounds could have been detected by hydrophones, given favourable circumstances. Sound waves can travel long distances in the ocean, but sounds that travel best are those that are reflected into the 'deep sound channel' usually found between 600–1,200 m beneath the surface. Most of the sound generated by an aircraft impacting the ocean would travel straight down to the seabed, making it unlikely that any of these sounds would be reflected into the deep sound channel unless the seabed sloped. Sounds from pieces of the aircraft imploding at depth would be more likely to travel in the deep sound channel. "The combination of circumstances necessary to allow [detection of an ocean impact] would have to be very particular", according to Mark Prior, a seismic-acoustic specialist at the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), who also explains that "given the continuing uncertainty regarding the fate of MH370, underwater acoustic data still has the possibility of adding something to the search." When an Airbus A330 hit the Atlantic Ocean at speed of 152 kn (282 km/h; 175 mph), no data relating to the impact was detected in hydroacoustic recordings, even when analysed after the location of that aircraft was known. As with the analysis of the Inmarsat satellite data, the hydroacoustic analysis uses the data in a way very different from that originally intended.

The Australian Transport Safety Bureau requested the Curtin University Centre for Marine Science and Technology (CMST) analyse these signals. Scientists from CTBTO and Geoscience Australia have also been involved with the analysis. Available sources of hydroacoustic data were:

• The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which operates a system of sensors to detect nuclear tests to ensure compliance with the Comprehensive Nuclear Test Ban Treaty. Data was analysed from CTBTO hydrophones located south-west of Cape Leeuwin, Western Australia (HA01) and in the northern Indian Ocean. These stations have two hydrophones each, separated by several kilometres, allowing a bearing to be calculated for the source of noise to within 0.5°.
• Australia's Integrated Marine Observing System (IMOS). Data from an acoustic observatory (RCS) 40 km west of Rottnest Island, Western Australia, near the Perth Canyon. IMOS stations have just one hydrophone each and therefore cannot provide a bearing on the source of the noise. Several IMOS recorders deployed in the Indian Ocean off northwestern Australia by CMST may have recorded data related to Flight 370. These recorders were not recovered as part of the investigation. These sensors record only five minutes out of every fifteen and are likely to be contaminated by noise from seismic surveys. CMST originally planned to recover the sensors in September or October, but now plan to make the trip in August.
• It is unclear what other sources of hydroacoustic data are available in the region. India and Pakistan operate submarine fleets, but the JACC claims they aren't aware of any hydrophones operated by those countries. The U.S. Navy operated a vast array of hydrophones—the Sound Surveillance System (SOSUS)—during the Cold War to track submarines, which is believed to remain in operation. Asked if any SOSUS sensors are located in the Indian Ocean, a spokesman for the U.S. Navy declined comment on the subject, noting that such information is classified.

Scientists from the CTBTO analysed their recordings soon after Flight 370 disappeared, finding nothing of interest. However, after the search for the flight shifted to the Indian Ocean, CMST collected recordings from the IMOS and found a clear acoustic signature just after 01:30 UTC on 8 March. This signature was also found, but difficult to discern from background noise, in the CTBTO recordings from HA01, likely because HA01 receives a lot of noise from the Southern Ocean and Antarctic coastline.

File:MH370 suspect hydroacoustic signal.png

Map of the Indian Ocean. Dots off the southwest corner of Australia indicate the location of hydrophone stations. The seventh arc and region of the underwater search is depicted west of Australia. The area of uncertainty where the hydroacoustic detection originated is a long, slim region in red running from the center of the coast of Arabia on the Indian Ocean to a point in the middle of the Indian Ocean, but far from the seventh arc and underwater search area.

The CMST researchers believe that the most likely explanation of the hydroacoustic data is that they come from the same event, but unrelated to Flight 370. They note that "the characteristics of the [event's acoustic signals] are not unusual, it is only their arrival time and to some extent the direction from which they came that make them of interest". If the data relates to the same event, related to Flight 370, but the arc derived from analysis of the aircraft's satellite transmission is incorrect, then the most likely place to look for the aircraft would be along a line from HA01 at a bearing of 301.6° until that line reaches the Chagos-Laccadive Ridge (approximately 2.3°S, 73.7°E). In the latter possibility, if the acoustic recordings are from the impact of the aircraft with the ocean, they likely came from a location where water is less than 2,000 m deep and the seabed slopes downwards towards the east or southeast; if they came from debris imploding at depth, the source location along this line is much less certain. The lead CMST researcher believed the chance the acoustic event was related to Flight 370 to be very slim, perhaps as low as 10%. The audio recording of the suspect detection was publicly released on 4 June 2014; the ATSB had first referenced these signals in a document posted on its website on 26 May.

Underwater locator beacons

The aircraft's flight recorders were fitted with Dukane DK100 underwater acoustic beacons—also known as "underwater locator beacons" (ULBs) or "pingers"—which are activated by immersion in salt water and thereafter emit a 10 millisecond pulse every second at frequency of 37.5±1 kHz. The beacons are limited by battery life, providing a minimum of 30 days and have an estimated maximum life of 40 days, according to their manufacturer. The nominal distance at which these beacons can be detected is 2,000–3,000 metres. Because the flight recorders to which they are attached could provide valuable information in the investigation, an intense effort was made to detect the beacons' pings before their batteries expired.

HMS Echo made one possible detection on 2 April—the same day the ship joined the search effort. The following day, following tests, the detection was dismissed as an artefact of the ship's sonar system. On the afternoon of 5 April Perth time, HMS Echo detected a signal lasting approximately 90 seconds. The second detection was made within 2 km from the first detection.

MV Haixun 01, operated by the China Maritime Safety Administration, detected a signal at 37.5 kHz pulsing once per second on 4 April and again on 5 April at a position 3 km west of the first detection. HMS Echo was sent to the location of the MV Haixun 01 detections and determined that the detections were unlikely to originate from ULBs attached to the plane's black boxes due to the depth of the seafloor, surface noise, and the equipment used. A submarine sent to the location made no acoustic detections.

File:TPL-25.jpg

The towed pinger locator on the deck of a vessel. An inset shows a rack of electrical equipment.

ADV Ocean Shield was sent to the search area with two Phoenix International TPL-25 towed pinger locators (also known as "towfish"). Shortly after one of the towfish was deployed, while descending, an acoustic signal was detected at a frequency of 33 kHz on 5 April. Further detections were made on 5 April and on 8 April, but none could be detected when the ship passed the same location on an opposing heading.

Independent analyses of the detections made by ADV Ocean Shield determined that the signals did not match the performance standards of the ULBs attached to the aircraft's black boxes. However, although unlikely, they noted that the signals could have originated from a damaged ULB.

Between 6–16 April, AP-3C Orion aircraft of the Royal Australian Air Force deployed sonobuoys, which sank to a depth of 300m to detect the acoustic signature of the ULBs attached to the aircraft's black boxes. Sonobuoy drops were carried out at locations along the calculated arc of the final satellite communication with Flight 370 where seafloor depths were considered favourable, near the MV Haixun 01 detections, and along the bearing determined by the Curtin University research team of a possible impact event. One AP-3C Orion sortie was capable of searching an area of 3,000 square kilometres (1,200 sq mi). No acoustic detections related to the ULBs attached to the aircraft's black boxes were made by the sonobuoys.

The interim report released by the Malaysian Ministry of Transport in March 2015 mentioned, for the first time publicly, that the battery for the ULB attached to the flight data recorder had expired in December 2012. The battery's (and thus the ULB's) performance may have been compromised, but this likely was not significant in the search, given the close range at which the detection must be made and the vast search area.

Search timeline

Main article: Timeline of Malaysia Airlines Flight 370

8 March 2014

Flight 370 disappears after departing Kuala Lumpur at 00:41 MYT (16:41 UTC, 7 March). A search and rescue effort is launched in the South China Sea and Gulf of Thailand.

9 March

Malaysia's military announces that Flight 370 may have turned back and flew west towards Malaysia. The search is expanded to include the Strait of Malacca.

12 March

Malaysia announces that Flight 370 crossed the Malay Peninsula and was last spotted on military radar 200 nmi (370 km; 230 mi) northwest of Penang on Malaysia's west coast. The focus of the search is shifted to the Andaman Sea and Strait of Malacca.

15 March

Officials announce that communications between Flight 370 and a communications satellite operated by Inmarsat indicate it continued to fly for several more hours and was along one of two corridors at the time of its last communication.

18 March – 28 April

Aerial search of the southern Indian Ocean, west of Australia, is conducted.

24 March

Prime Minister of Malaysia announces that Flight 370 is presumed to have gone down in the southern Indian Ocean; Malaysia Airlines states to families that it assumes "beyond reasonable doubt" there are no survivors. The northern search corridor (northwest of Malaysia) and the northern half of the southern search corridor (the waters between Indonesia and Australia) are definitively ruled out.

30 March

The Joint Agency Coordination Centre is created to coordinate the multinational search effort.

2–14 April

An intense effort by several vessels and aircraft-deployed sonobuoys is made to detect underwater acoustic signals made by underwater locator beacons attached to the aircraft's data recorders. Several acoustic detections are made between 4–8 April.

14 April−28 May

A sonar survey of 860 km² (330 sq mi) of seafloor near the 4–8 April acoustic detections is conducted, yielding nil debris.

File:Bathymetry of the MH370 Search Area.webm

Video tour of bathymetry data collected during the bathymetric survey.

May–December

A bathymetric survey is conducted in the region where the underwater search will be carried out.

26 June

Plans for the next phase of the search (the "underwater search") are announced to the public in-depth for the first time and the Australian Transport Safety Bureau (ATSB) releases a report detailing the previous search efforts, analysis of satellite communications, methodology used to determine the new search area.

October−ongoing

The underwater search began on 6 October and is expected to last up to 12 months. The search is conducted in areas where the bathymetric survey has been completed.

8 October

Officials announce that the priority area to be searched is further south of the area identified in the June ATSB report. The ATSB releases a report (a supplement to the June report) that details the methodology behind refinements to the analysis of satellite communications.

22 January 2015

The ATSB calls for expressions of interest for recovery operations of Flight 370, so that a recovery effort can be mobilised quickly and effectively if and when debris from Flight 370 is located. The request will allow the ATSB to determine which organisations can supply the equipment and necessary expertise for the recovery effort.

29 July

A piece of marine debris, thought to be a flaperon from a Boeing 777, is found on Réunion Island.

5 August

The Malaysian Prime Minister announces that experts have "conclusively confirmed" that the debris found on 29 July is from Flight 370; the debris is the first physical evidence that Flight 370 ended in the Indian Ocean.

6 August

Malaysia's Transport Ministry claims that window panes and aircraft seat cushions have washed up on Réunion. This claim is disputed by France.

7 August

Maldivian police investigate claims that plane debris has washed up on North Malé Atoll, Maldives. Authorities in nearby Mauritius have also begun searching for debris and sent a piece of a bag found on Îlot Gabriel for inspection.

12 August

A packet of Malaysian noodles were found in South Australia and a Malaysia Airlines baggage tag was found in Nowra, New South Wales. The items were turned into Australian authorities, who noted that "It’s very challenging for investigators to find something that can be linked to the aircraft — it would really have to be some form of debris from the aircraft. But we encourage people to bring anything unusual or out of place forward. It’s far better that we investigate and rule it out."

The debris from North Malé is flown to Malaysia for investigation.

Malaysia's government news agency published a new theory that Flight 370 made a soft landing on the water, floated for a while on the surface, and then sank mostly in one piece. Many experts also believe in this theory.

3 September

French investigators affirm "with certainty" that the aircraft flaperon discovered on 29 July is from Flight 370, due to a serial number that matched the records of the Spanish manufacturer that produced portions of the flaperon.

8 September

Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) releases a drift analysis that concludes that the finding of the flaperon on Réunion is consistent with the current search area for Flight 370.

3 December

Australian Deputy Prime Minister Truss announces the number of vessels in the search would be doubled to four, and that the undersea search was expected to be completed by June 2016. The JACC release an updated report on the undersea search area.

19 December

A second 19th-century shipwreck is discovered.

19 April 2016

The ATSB issue a report on the debris found in Mozambique.

12 May

The ATSB issue an updated report on debris found in South Africa and Mauritius to confirm identification.

See also

• Air France Flight 447 – Crashed into the Atlantic Ocean in 2009. After several extensive searches, the fuselage and flight recorders were discovered two years later.
• Flying Tiger Line Flight 739 – Disappeared over the Pacific Ocean. Despite one of the largest ever search and rescue operations, the aircraft was never found.
• South African Airways Flight 295 – Crashed into the Indian Ocean in 1987. The search and recovery process took more than two years and was the deepest underwater search and recovery at the time.
• List of accidents and incidents involving commercial aircraft

External links

• Joint Agency Coordination Centre (JACC)
• Australian Transport Safety Bureau — MH370 – ATSB webpage for information about Flight 370
• MH370 – Definition of Underwater Search Areas – Report by the Australian Transport Safety Bureau, released 26 June 2014, and the most comprehensive report on Flight 370 publicly released at that time. The report focuses on defining the search area for the fifth phase, but in doing so provides a comprehensive overview/examination of satellite data, the failed searches, and possible "end-of-flight scenarios".
• MH370: Bathymetric Survey – Information about the bathymetric survey from Geoscience Australia
• Timeline of AMSA's involvement

Press releases / Media

• Australian Maritime Safety Authority
• Australian Transport Safety Bureau
• Malaysia Airlines
• Malaysian Ministry of Transport
• US Department of Defense