How Do You Track A Plane?


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By BBC 14 March 2014 Last updated at 11:58
Mystery continues to surround the fate of Malaysia Airlines flight MH370, which disappeared without trace more than a week ago.

The Boeing 777-200ER plane, with 239 people on board, vanished from air traffic control screens at approximately 01:20 local time on Saturday 8 March - just an hour after leaving Kuala Lumpur bound for Beijing.

Concrete facts about what happened remain elusive. A variety of theories have been put forward, from hijacking or sabotage, to a slow loss of cabin pressure, which in turn could cause the crew and passengers to become disorientated.

But, with no debris yet identified, much of the search has been focused on the last-known movements of the aircraft.

So, how do you track a plane and what do we know about the movements of flight MH370?
Air traffic control standard international practice is to monitor airspace using two radar systems: primary and secondary.

Primary radar, based on the earliest form of radar developed in the 1930s, detects and measures the approximate position of aircraft using reflected radio signals. It does this whether or not the subject wants to be tracked. Secondary radar, which relies on targets being equipped with a transponder, also requests additional information from the aircraft - such as its identity and altitude.

All commercial aircraft are equipped with transponders (an abbreviation of "transmitter responder"), which automatically transmit a unique four-digit code when they receive a radio signal sent by radar.

The code gives the plane's identity and radar stations go on to establish speed and direction by monitoring successive transmissions. This flight data is then relayed to air traffic controllers.

However, once an aircraft is more than 240km (150 miles) out to sea, radar coverage fades and air crew keep in touch with air traffic control and other aircraft using high-frequency radio.

Flight MH370 disappeared from air traffic control screens when its transponder signal stopped. The last definitive sighting on civilian radar showed the plane flying north east across the Gulf of Thailand.

The final radio message received by air traffic control - "Alright, roger that" - suggested everything was normal on board.

Don't planes have GPS?

Yes, but while GPS (Global Positioning System) is a staple of modern life, the world's air traffic control network is still almost entirely radar-based.

Aircraft use GPS to show pilots their position on a map, but this data is not usually shared with air traffic control.

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I am not sure if this is the correct section, may be combined with other news, not sure. It is up to Mods. :)

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