India used heat sensors on flights over hundreds of Andaman Sea islands such as North Sentinel Island and will expand its search for the missing Malaysia Airlines jet farther west into the Bay of Bengal, officials said. Credit:AP Photo This indicates that it was either being flown by the pilots or someone with knowledge of those waypoints, the sources said. The last plot on the military radar's tracking suggested the plane was flying toward India's Andaman Islands, a chain of isles between the Andaman Sea and the Bay of Bengal, they said. Waypoints are geographic locations, worked out by calculating longitude and latitude, that help pilots navigate along established air corridors. A third source familiar with the investigation said inquiries were focusing increasingly on the theory that someone who knew how to fly a plane deliberately diverted the flight.

Outpouring of emotion ... A woman writes a message on a banner for passengers of missing Malaysian Airlines Flight 370 at Kuala Lumpur International Airport (KLIA) in Sepang, Malaysia. Credit:Bloomberg POSSIBLE SABOTAGE OR HIJACK "What we can say is we are looking at sabotage, with hijack still on the cards," said that source, a senior Malaysian police official. Flights continue ... A Boeing 737-800 aircraft operated by Malaysian Airlines is prepared for take off at Kuala Lumpur International Airport (KLIA) in Sepang, Malaysia. Credit:Bloomberg All three sources declined to be identified because they were not authorized to speak to the media and due to the sensitivity of the investigation.

Officials at Malaysia's Ministry of Transport, the official point of contact for information on the investigation, did not return calls seeking comment. Malaysian police have previously said they were investigating whether any passengers or crew had personal or psychological problems that might shed light on the mystery, along with the possibility of a hijacking, sabotage or mechanical failure. As a result of the new evidence, the sources said, multinational search efforts were being stepped up in the Andaman Sea and also the Indian Ocean. ANDAMAN ISLANDS Indian aircraft on Friday combed Andaman and Nicobar, made up of more than 500 mostly uninhabited islands, for signs of the missing jetliner that evidence suggests was last headed towards the heavily forested archipelago.

Popular with tourists and anthropologists alike, the islands form India's most isolated state. They are best known for dense rainforests, coral reefs and hunter-gatherer tribes who have long resisted contact with outsiders. The Indian Navy has deployed two Dornier planes to fly across the island chain, a total area of 720 km (447 miles) by 52 km (32 miles), Indian military spokesman Harmeet Singh said in the state capital, Port Blair. So far the planes, and a helicopter searching the coast, had found nothing. "This operation is like finding a needle in a haystack," said Singh, who is the spokesman for joint air force, navy and army command in the islands. NARROW CORRIDOR The Defence Ministry said the Eastern Naval Command would also search across a new area measuring 15 km by 600 km along the Chennai coast in the Bay of Bengal.

The shape of this area, located 900 km west of Port Blair, suggested the search was focusing on a narrow flight corridor. On standby is India's most advanced maritime air surveillance plane, the P-8I Poseidon, a long range anti-submarine variant of the U.S. Navy's P-8A. India, the first overseas customer for the aircraft, has ordered eight P-8Is. Indian ships are also helping in the search by more than a dozen nations for the missing plane, by looking in an area north of Sumatra, in the south Andaman Sea. The 2004 Asian tsunami devastated much of Andaman and Nicobar. In the wake of that disaster, a member of the reclusive Sentinelese was photographed shooting arrows at an Indian coastguard helicopter. Another nomadic tribe, the Jarawa, are increasingly in contact with outsiders. Tribal rights group Survival accuses travel agencies of organising "human safari" tours to view the Jarawa, who are fish and turtle hunters and number about 400.

Andaman and Nicobar is of strategic importance for India, because of its location near the busy Malacca Straits shipping route. Over the past decade, India has built up its military presence on the islands. LAST SIGHTING In one of the most baffling mysteries in modern aviation, no trace of the plane nor any sign of wreckage has been found despite a search by the navies and military aircraft of more than a dozen countries. The last sighting of the aircraft on civilian radar screens came shortly before 1.30am. Malaysian time last Saturday (1730 GMT Friday), less than an hour after it took off from Kuala Lumpur, as the plane flew northeast across the mouth of the Gulf of Thailand. That put the plane on Malaysia's east coast. Malaysia's air force chief said on Wednesday an aircraft that could have been the missing plane was plotted on military radar at 2.15am, 320 kilometres northwest of Penang Island off Malaysia's west coast.

This position marks the limit of Malaysia's military radar in that part of the country, a fourth source familiar with the investigation said. When asked about the range of military radar at a news conference on Thursday, Malaysian Transport Minister Hishammuddin Hussein said it was "a sensitive issue" that he was not going to reveal. "Even if it doesn't extend beyond that, we can get the co-operation of the neighboring countries," he said. The fact that the aircraft - if it was MH370 - had lost contact with air traffic control and was invisible to civilian radar suggested someone on board had turned off its communication systems, the first two sources said. They also gave new details on the direction in which the unidentified aircraft was heading - following aviation corridors identified on maps used by pilots as N571 and P628. These routes are taken by commercial planes flying from Southeast Asia to the Middle East or Europe and can be found in public documents issued by regional aviation authorities.

In a far more detailed description of the military radar plotting than has been publicly revealed, the first two sources said the last confirmed position of MH370 was at 10,600 metres about 145 kilometres off the east coast of Malaysia, heading towards Vietnam, near a navigational waypoint called "Igari". The time was 1.21am. The military track suggests it then turned sharply westwards, heading towards a waypoint called "Vampi", northeast of Indonesia's Aceh province and a navigational point used for planes following route N571 to the Middle East. From there, the plot indicates the plane flew towards a waypoint called "Gival", south of the Thai island of Phuket, and was last plotted heading northwest towards another waypoint called "Igrex", on route P628 that would take it over the Andaman Islands and which carriers use to fly towards Europe. The time was then 2.15am. That is the same time given by the air force chief on Wednesday, who gave no information on that plane's possible direction. Loading

The sources said Malaysia was requesting raw radar data from neighbours Thailand, Indonesia and India, which has a naval base in the Andaman Islands. Reuters