How Boeing plane stays in contact

How Boeing plane stays in contact

It is one of the most modern and technologically advanced aircraft ever built.


So it is a mystery how Malaysia Airlines Flight MH370, a very "talkative" Boeing 777-200, is still missing since losing contact with air traffic controllers on March 8.

This is how the Boeing plane usually stays visible - and in contact - throughout its flight.


Located in the cockpit, the transponder transmits discreet signals picked up by radar at air traffic control. The Boeing 777 is equipped with two transponders.

If one fails, a warning message will show and the crew can select the second one. However, transponders can be turned off - manually - at any time.


Located at the back of the plane is an indestructible flight data recorder (also known as a black box, even though it is painted bright orange for visibility) that captures all instructions sent to any electronic systems on the aircraft.

It also records sounds in the cockpit and data like the plane's altitude, air speed, vertical acceleration and heading.

It is fitted with an underwater locator beacon (or pinger) that activates automatically when submerged, for up to 30 days and a depth of 6,000m.


Air traffic controllers use radar to monitor aircraft. There are two kinds: the primary radar which sends out radio waves that bounce off aircraft to determine their location (aircraft will appear as blips on the radar screen), and the secondary radar that communicates with the transponders.

When an aircraft picks up radio waves from the secondary radar within a 300km range, its transponder sends back a unique four-digit code (called a squawk) that identifies the plane.

The primary radar is usually used by the military, and the secondary radar for civil aviation.


Pilots talk to ground controllers - and other aircraft - using radio signals transmitted over ultra-high frequencies or very high frequencies.


Pilots use Global Positioning System (GPS) satellites to navigate and determine where they are, but the information is not transmitted elsewhere.


The Aircraft Communications Addressing and Reporting System, or ACARS, allows pilots to send simple short text messages transmitted through radio signals and satellites.

It also sends data about engine performance to its manufacturers.


The ADS-B (Automatic Dependent Surveillance-Broadcast) is a new type of flight surveillance system that captures radio waves constantly sent out by ADS-B transponders, which are usually attached to the bottom of the plane.

The radio waves contain GPS information, the flight number, speed and vertical velocity. Although it is not a global standard, most planes are already fitted with these transponders, which flight-tracking services rely on for flight data.

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