Air traffic control (ATC) – ATC as a standard practice, to monitor aircrafts uses two radar systems, primary and secondary.
Primary radar -By using the reflected radio signals an approximate position of the aircraft is detected. In this case subject has an option of getting traced or not.
Secondary radar, works similar to the primary radar but it is equipped with a transponder, that transmits its identity and altitude as well.
Whenever a transponder receives a signal from radar, it automatically broadcast a unique 4 digit code corresponding to the plane’s identity.
As the radar stations receives the code, they ascertain the speed and direction by observing the successive transmissions. This flight data is then communicated to ATC.
There is a limit to transmission and receiving the signals via radar and is commonly known as line-of-sight. The line-of-sight or the range beyond which the radar coverage fades away is 150 miles. At that time the aircraft uses high-frequency radio waves to establish the contact with ATC.
Why can’t aircraft be tracked real-time using GPS ?
As of now aircraft’s pilot uses GPS to locate their position but it is not usually shared with ATC.
Now a day’s Automatic Dependent Surveillance – Broadcast (ADS–B) is used in the aircrafts. As a part of it, GPS transmits aircraft’s position twice per second. The problem here is receiver’s coverage , as it won’t work beyond the line-of-sight . It is quite expensive to provide coverage over the large water bodies.
To overcome this issue a concept is being proposed by Thales Alenia Space and Iridium (Aireon) to install receivers on satellites. The system is expected to be operational in 2018.
Aireon is going to place ADS-B receivers on the Iridium NEXT constellation, that comprises of 66 Low Earth Orbit (LEO) satellites. To achieve 100% global air traffic surveillance irrespective of terrain, location or infrastructure, these space-based ADS-B receiver set-up will transmit signals from all ADS-B equipped aircraft to controllers globally.
To know about the health of the aircraft’s system, there is Aircraft Communications Addressing and Reporting System (ACARS).
ACARS is used by onboard plane computers to communicate with computers on the ground, giving information about the systems health.
Radio or digital signals via satellites are used to communicate through messages, and can send information of any kind of system ranging from engine’s fault to any minute system fault. This gives important diagnostic information to the ground crews which can expedite the maintenance process.