Air Traffic Control System

By Hassan Ali Khan(5097)

Topics of Discussion

• What is ATC?• History of ATC.• Types of Radars used in ATC.• ATC Operating Frequencies.• ATC Transponder Modes.• ATC Airborne Equipment• ADS-B• Emergency ATC Transponder Codes.• Busiest ATC in the world.

ATC(Air Traffic Control)

• It is a service provided by ground-based controllers who direct aircraft on the ground and through controlled airspace.

• Primary purpose of ATC systems worldwide is to prevent air traffic collisions.

• To organize the flow of traffic.• Provide Information and other support to pilots.• It plays a security or defensive role when

operated by military.

History of ATC

• In 1921, Croydon Airport, London was the first airport in the world to introduce air traffic control.

Types of Radars used in ATC

• PSR(Primary Surveillance Radar) only indicates the position of the targets, it does not identify them. Inefficient because transmitted energy is large compared to reflected energy. Only range and azimuth information. 2700 to 2900 MHz operating Frequency.

• SSR(Secondary Surveillance Radar) relies on targets equipped with a radar transponder, that replies to each interrogation signal by transmitting a response containing encoded data. Based on IFF system. It also tells identity and altitude.

PSR SSR

ATC Operating Frequencies

• Operates on two frequencies within L-band.

• Interrogation codes on 1030 MHz carrier wave.

• Reply codes on 1090 MHz carrier wave.

ATC Transponder Modes

• Mode A tells 2D information. Azimuth is shown on the controller’s screen.

• Mode C tells 3D information. Azimuth and Pressure Altitude on the controller’s screen.

• Mode S works on roll call principle. It allows specific aircraft to be interrogated and only that specific aircraft replies so it has increased efficiency. Uses monopulse SSR. Only require single pulse.

• Mode A and C format • Mode S ‘all call’ format

• 0.8 us for Mode A or C ‘all call’• 1.6 us for Mode A/S or C/S

‘all call’

ATC Airborne Equipment

• Commercial aircrafts contain 2 ATC antennas, 2 transponders and a control panel.

• One Antenna is at top of aircraft and the other one is at the bottom.

• ATC and DME both operate in same frequency so a circuit is utilized which prevent the interference.

ADS-B

• It’s a NextGen System.• Intended to replace SSR.• Provides surveillance where ground coverage is

not possible, e.g. over oceans.• Uses GNSS.• 90% cost effective and fuel efficient system.• Unlike radar, ADS-B accuracy does not seriously

degrade with range, atmospheric conditions, or target altitude.

• Squitter – Mode-S transponders send periodic burst transmissions called "squitter". These are not a result of interrogations from the secondary surveillance radar.

• Extended Squitter – is a set of messages used to broadcast an aircraft's GPS position, navigation system status, projected path, and identity so that other aircraft, and controllers, can track the aircraft with a high degree of accuracy.

• VHF digital link(VDL) – is a means of sending information between aircraft and ground stations. Suited for short message transmissions from large no. of users over longitude range. Uses Glonass to send messages.

ATC Emergency Transponder Codes

• 7700 – General Air Emergency.

• 7600 – Loss of Radio.

• 7500 – Hijacking

Busiest ATC in the World

OSHKOSH, Wisconsin USA

The End