Radar communication system

Radar

Radar is actually an acronymthat stands for RAdio Detection And Ranging. It was developed in the early 1940s. Radar uses the echo principle.Radar equipment emits a high energy radio signal from an antenna. The signal travels out from the source untilit is reflected back by contact with an object. The radar antenna relays this signal to a scope where the imageis displayed. Using the time it takes for the emitted signal to reach the object and reflect back to its source,the distance to the object can be computed. The radar signal is moving at the speed of light and can make sucha trip in microseconds.

In aviation, a ground radarantenna sends radio signal pulses into the sky. These signals are reflected back by aircraft flying in the airspace.The radar scope displays the direction and distance from which the signals are reflected back. This coupled witheach aircraft's transponder signal identifies the aircraft on the radarscope. Also, all airliners are equippedwith radar equipment in the aircraft's nose. Short bursts of radio signals are emitted from the nose cone of theaircraft. These signals reflect off clouds ahead of the aircraft. The on-board computer calculates the distanceand displays the object (the cloud) on the on-board radar screen.

The Flight PlanCommercial airline companies employ flight planners who perform all the necessary data gathering and analyses necessaryto complete a flight plan. These flight plans are then given to the pilots during a flight briefing before thepilot begins the aircraft preflight check. These flight plans contain information similar to what is required fora small aircraft pilot's flight plan. Small aircraft pilots and charter pilots perform their own flight planning and submit their flight plans to the Flight Service Station (FSS) that services their departure airport. The FSS enters the flight plan information into their system. Among the many services offered by the FSS, it is responsible for processing flight plans. After a pilot files a flight plan with an FSS facility, a record of the flight plan is made that includes the aircraft description and tail numbers, departure and destination airports, route of flight, estimated time of departure (ETD), estimated time of arrival (ETA) and number of people on board. About an hour before takeoff or once airborne, the pilot "opens" the VFR flight plan. This ensures that the FSS will keep track of the airplane's ETA. Along the route the pilot radios the FSS with occasional position reports. This helps the FSS to track the route. If the pilot gets disoriented along the way, an FSS specialist could locate the aircraft with a VHF direction finder or use radar. Within thirty minutes of completing a flight, the pilot needs to close the VFR flight plan. If the pilot changes the final destination or will be at least 15 minutes later than estimated, the pilot needs to inform the FSS facility accordingly. If the pilot does not close the flight plan or indicate changes to the FSS, the FSS will initiate search and rescue procedures believing the aircraft has been "lost".

Flight Tracking Strip and Data BlockUpon acceptance of a flight plan for a commercial jetliner flight, a "flight tracking strip" is generated in the departure control tower. This strip contains essentially the same information from the flight plan, but in an abbreviated format. This strip communicates to air traffic controllers along the route information about the flight that assists controllers in directing the pilot. This strip is physically handed off from controller to controller within the same air traffic management facility (such as the local control tower). It is also electronically handed off from one air traffic management facility to another as the flight moves from one airspace sector to another.Each air traffic management facility has a slightly different look for their flight tracking slips.

Every commercial flight is equipped with a transponder. This electronic device is connected to the on-board computer. It transmits coded radio signals to the controller's radar receiver. These signals contain information about the flight: aircraft's identification letters or flight number and its altitude. Upon departure, pilots receive a 4-digit transponder code and set their transponder to that code. The terminology is "Squawk" 1200. The standard transponder code for VFR flights is 1200. When the code is set, the radar "blip" for that flight shows as an enhanced signal on the controller's radar screen. The aircraft is shown in motion on the screen and is followed by a box with the flight's information in it: the data block. This way controllers can visually track each flight as it flies through their designated airspace.