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Air Traffic Control
HindustanTimes.com, PTI
May 21, 2003
First Published: 16:30 IST(21/5/2003)
Last Updated: 16:32 IST(21/5/2003)

"Cleared to land runway… Two Seven, wind Two Nine Zero degrees One Two (12) knots… 

The soft and relaxed voice from the ground has a soothing effect on the pilot who completes his tiring journey by making a successful landing. It's a wonder for many how an aircraft reaches its final destination from a departure station, who all are involved in the process of safe flight and landing?

It is understandable if they assume that the pilot is the person who takes care of everything from take off, en route flying and landing. People in general know about the pilot, but much less about those who remain behind the screen and shoulder the responsibility of guiding the flights from the starting an engine at departure aerodrome to its landing at destination.

THE ORIGIN OF ATC

By the end of the first decade of powered flight, people began to realise that aircraft, like automobiles, would crash into each other unless some means was developed to control and direct them.

At first, because aircraft could not fly very high, such control was accomplished using simple hand signals. Later, control was exercised through radio communication.

By the end of World War II, the invention of radar permitted visually displayed tracking of several aircraft at once. When coupled with radio communication, radar made it possible for the pilot to be warned when he was in danger of colliding with another aircraft or when he was off course. Today, aircraft are continually tracked from take-off to landing

HISTORY OF AIR TRAFFIC CONTROL

Archie William League (1907-1986), is widely acknowledged as the first US air traffic controller with his claim to the first air traffic controller largely unchallenged. After becoming a licensed airplane and engine mechanic, flying and barnstorming around Illinois and Missouri with his own 'flying circus' , Archie was hired by the city to direct the growing air traffic at St. Louis's Lambert Field.

His "control tower" was a wheelbarrow on which he mounted a beach umbrella for the summer heat. In it he carried a beach chair, his lunch, water, a note pad and a pair of signal flags to direct the aircraft either to 'GO' or 'HOLD'. In the winters, he wore a padded flying suit to keep warm out on the field.

However, with improvements in airplanes from Orville and Willbur Wright's first flight in 1903 to the dawn of Jet Age in 1930 and supersonic aircrafts in 1968 , lot of newer gadgets came into being to ease Air Traffic Control.

It started with humble introduction of Light Beacons. In 1921, the US Army deployed rotating beacons in a line between Columbus and Dayton, Ohio, a distance of about 80 miles.

The beacons, visible to pilots at 10-second intervals, made it possible to fly the route at night. The US Post Office took over the operation of the guidance system the following year, and by the end of 1923 constructed similar beacons between Chicago and Cheyenne, WY, a line later extended coast-to-coast .

Another development of enormous importance to aviation was radio. Aviation and radio developed almost in lock step. Marconi sent his first message across the Atlantic on the airways just two years before the Wright Brothers' first flight at Kitty Hawk.  By World War I, some pilots were taking radios up in the air with them so they could communicate with people on the ground.

The airlines followed suit after the war, using radio to transmit weather information from the ground to their pilots so they could avoid storms.

Perhaps an even bigger development, however, was the realization that radio could be used as an aid to navigation when visibility was poor and visual navigation aids such as beacons were useless.

Once technical bugs were worked out, the US Department of Commerce constructed 83 radio beacons across the USA.  They became fully operational in 1932, automatically transmitting directional beams, or tracks, that pilots could follow to their destination. Marker beacons came next, allowing pilots to locate airports in poor visibility. These beacons in the form of NDB and VOR provide the homing and holding facility to the aircraft.

In the beginning the cockpit crew had only one reliance for landing an aircraft. to lookout for the runway and make approach for landing keeping Runway in view. Continued progression in the electronics, gifted the aviation industry with what can be termed as additional pair of eyes for the cockpit crew to be used when it is dark, foggy or otherwise a situation when visual reference may not be possible.

These are Precision Approach facilities, like PAR, ILS and MLS. PAR (Precision Approach Radar) had two Radar antennas one in vertical plane other in horizontal plane to give a continued picture of an aircraft in the approach path, indicating position of aircraft with reference to centerline of runway and its descent profile. However it needed a controller to give a running commentary to the pilot about his position with regard to runway, and was dependent on many things between pilot and his aircraft. That is, the Radar Equipment, the controller on ground using this Radar, Radio communication between aircraft and controller, pilot's more pressing need to attend to aircraft rather than to the rattling by the controller.  All these were the drawbacks of PAR. however it gat replaced with ILS and MLS soon enough.   

ILS and MLS are essentially close to each other with exception of MLS being superior over ILS and is some conditions an option available when ILs can not be used. However both these are Pilot interpreted precision approach facilities. Meaning thereby these systems do not need a controller to give any rattling any more. The Equipment consists of two antenna transmitting radio beams in horizontal and vertical plane. An onboard radio receiver installed in the cockpit gives indication to the pilot about his position with reference to runway. This equipment follows the normal principle of cockpit instruments, follow the needle, that is if needle is down - go down, if needle is left - go left.

RADAR
  
A technological development with a much greater impact on the world war's outcome (and later on commercial aviation) was radar.  British scientists had been working on a device that could give them early warning of approaching enemy aircraft even before the war began, and by 1940 Britain had a line of radar transceivers along its east coast that could detect German aircraft the moment they took off from the Continent. 
  
Introduction of Radar in the air traffic control has definitely eased the job of Controllers as well as Pilot. These equipments with ultra modern technology now available, provide a controller with a three dimensional picture, and also gives predicted course, traffic convergence warning etc. Though not many nations have so far completed the installation of Radar System that will cover all of the airspace under their respective jurisdiction, the ultimate goal, under FANS project (Future Air Navigation System) is to give a global surveillance system by use of composite radar system and satellite tracking system.


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