The area, the location
* The main search area covered 470,000 square nautical miles in the southern Indian Ocean till Friday. It is one of the most isolated regions in the world, far from any land, airline routes.
* The predominant winds and ocean currents there would move the debris in an easterly direction from the presumed crash site. The speed would depend on the strength of winds and the speed of surface and subsurface currents. On Friday, the search area saw another shift, 1,100 km to the north-east, closer to land.
* The southern corridor of the Indian Ocean ranges in depth from 3,770 feet to 23,000 feet.
* There are volcanic ridges rising up from the ocean floor. The Southeast Indian Ocean Ridge cuts through the search area, meaning the sea bed is rugged and constantly being reshaped by magma flows. Experts hope the wreckage is lying on a flat area, as a search operation becomes complicated if objects are lodged in a ravine or mountainous area. Geological features can hinder sonar (Sound Navigation and Ranging) and obscure debris.
Search planes are having to fly with and against a wind system called the Roaring Forties, which circle the earth at 30-40 mph, moving west to east. The search area is characterised by high waves and swift undercurrents.
Ocean currents move west to east in loops and eddies in southern hemisphere, and can carry material 50-60 miles. This is the location of Indian Ocean Gyre, an area of circular ocean current.
* The planes black box sends out a ping activated by immersion in water that can be picked up. The emergency locator transmitter sends out a distress signal on impact. The voice recorder and data recorder each have their own pinger. But theres a problem the battery of the pinger on MH370 will only last 30 days.
* The search will try to locate the wreckage before moving in to pinpoint the black box by picking up the ping. If the pinger has expired then, other techniques such as magnetic detection will be necessary. But the box is small and heavy, about 10 kg. Made of aluminium, it is designed to withstand massive impact and will sink quickly.
* Honeywell, which made MH370s pinger, says the signal can only be picked up a mile away. This means aircraft need to be almost directly on top of the black box to hear the ping. And thats discounting possible wreckage on the surface, or the black box being submerged in mud.
* If the pinger is at the ocean floor, navies have hydrophone technology to listen in. But if the pings hit a layer of warmer or colder water above, the signal might be refracted or reflected.
Over the open ocean, such images are limited in the amount of detail they can provide. Besides, satellites pass over this part of the Indian Ocean only periodically, so it is unlikely one of them would have registered the moment MH370 entered the ocean.
Knowing whether an object in a satellite photo is aircraft debris or a piece of rubbish (there is a lot around) is also very difficult.
Britains Inmarsat used a wave phenomenon discovered in the 19th century to analyse the seven pings its satellite picked up from MH370 to determine its final destination. The company used the doppler effect the change in frequency of a transmission due to movement of a satellite or aircraft. When this data was compared with data for the known paths of other aircraft, the likely route taken by MH370 was established.
The French example
In June 2009, Air France flight 447 went missing flying from Rio de Janeiro to Paris. Two years later, Frances aviation accident investigation authority BEA sought out US statisticians with expertise in finding objects lost at sea. Colleen Keller and her team relied on Bayesian statistics named after an 18th-century British Presbyterian minister, Thomas Bayes. This thinking allows one to assess various scenarios at once to give the most likely solution.