Radio Communication: A-Z of Air Traffic Control

Air traffic control (ATC) began in the 1930's with a system that used teletype machines, wall sized blackboards, large table maps and markers representing airplanes. Controllers used the markers across the map to estimate the position of the aircraft. 

Although a radar system was developed during WWII, the procedures of the ATC were yet manual. Controllers were required to spend nearly 75% of their time in voice communication and in-flight progress. But when the radar system was combined with computers and aircraft transponders, ATC services became more effective.

by Sonalee Sarkar
1 year, 3 months ago
1

Avionics are the electronic system used by an aircraft for its communication. Avionics is a combination of two words i.e. aviation and electronics. It not only helps in communication but also helps todisplay the number of other systems used by the aircraft for the aircraft to perform in proper and functional manner. The cockpit is the main area where the avionic system is located. If there is absence of the avionic system in the cockpit there will be no proper flying of the aircraft as you will not be able to the determine the altitude, speed, degree of turns, the path to follow, to know if there is any other aircraft closer to you etc. International standards for avionics equipment are prepared by the Airlines Electronic Engineering Committee (AEEC) and published by ARINC. Avionic system helps in communication with both i.e. the flight crew with the ground crew also known as ATC (Air Traffic Control) and the flight crew with the passengers. The communication of the flight crew with the passengers is done with the help of the aircraft intercom. E.g. if you have traveled on a plane, before its take-off the crew explains the various safety measures, this explanation is given with the help of the intercom.

In today’s world automatic flight controls are used to reduce human error and also reduce the workload of the flying pilot. Automatic flight controls was first introduced by Lawrence Sperry during World War II to fly bomber planes so that it can hit the precised target. However now days most of the commercial planes do have automated flight controls.

Avionic system helps to find out the following:-

  • To find out the location of other aircrafts
  • To find out the closest ATC (Air Traffic Control) tower of the aircraft flying.
  • An ATC tower is said to be closest to the aircraft if it is not just within the     aircraft communication radio but the aircraft should be able to actively    communicate with the ATC.
  • To help to find out the flight plan so that the flight can be manoeuvred accordingly.

These are just a few examples. There are many more uses of the system.

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2

Radar(radio detention and ranging) makes use of radio waves to determine the range, altitude, direction or speed of the aircraft.

                                             Basic Flight Recorder

                                                            Antenna

A basic radar system as seen in the above diagram is spilt up into a transmitter, switch, antenna, receiver, data recorder, processor and some sort of output display. Everything starts with the transmitter as it transmits a wave to a switch which then directs the wave to be transmitted out to an antenna. After the antenna is finished transmitting the wave the switch switches control to the receiver which allows the antenna to receive the echoed signals.  Once the signals are received the switch then transfers control back to the transmitter to transmit another signal. The switch may toggle control between the transmitter and the receiver as much as 1000 times per second. Any received signals from the receiver are then sent to a data recorder for storage on a disk or tape.

Primary radar is used by the ATC which transmit waves like a marrow beam by a rotating antenna. The radar antenna is designed to both transmit radio waves and receive the reflected signals.  The waves transmitted by the ATC on the ground levels hit the flying aircraft and then these waves are reflected back to the antenna which then displays the location of the flying aircraft on the radarscope of the ATC. The range of the aircraft is determined by the distance it is from the antenna. In simpler words it measures the time the radio waves take to reach the aircraft and return to the receiving antenna. It is very essential for the ATC to know the location of the aircraft in order to avoid collision between two aircrafts. Primary radar have some limitations like it does not work well with small aircrafts, its range is limited by terrain, it does not detect if the object on way is a plane, tree, hill etc. and it does not even record the planes altitude.The Air Traffic Control Radar Beacon System (ATCRBS) is also called the secondary surveillance radar or simply secondary radar. They are used by the ATC for better monitoring of radar surveillance. They are mainly used for aircrafts at higher altitudes and where there high traffic areas. They cover the limitations of the primary radar.
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3

Transponder is a short form of transmitter responder. Transponders are also sometimes referred to as "beacons", and another name for secondary radar is "ATC Radar Beacon System" or ATCRBS (pronounced "at-crabs"). It is an electronic device that responses to the wave received from the ATC. This reply helps the ATC to find out where the aircraft is on the radar in order to avoid collision with other aircrafts. It is a regulation to test the transponder every 24 calendar months for operation in controlled airspace.

 You need to be familiar with the transponder in order to operate it correctly. Transponders have some several positions (buttons). They include Off, SBY (Standby), On, ALT (Altitude) and TST (Test). Transponders are four digit numbers that are sent by the transponder of the aircraft to the ATC so that it can help the ATC in controlling the air traffic. The term squawk is used by the ATC controller to assign a particular aircraft a code so that the aircraft can be easily tracked on the radar. E.g. A pilot may be requested to squawk a given code by the air traffic controller via the radio, using a phrase such as "Cessna 123AB, squawk 0363". The pilot then selects the 0363 code on their transponder and the track on the radar screen of the air traffic controller will become correctly associated with their identity. You should avoid codes like 7500, 7600 and 7700. This is because these codes have their own role to play and if these codes are set as a code on your transponder than it can bring a wrong alarm for the ATC controller. Roles played by the numbers are:-7500 sends an alarm to the ATC that an aircraft has been hijacked, 7600 means a failure of both ways communication and 7700 is used for other emergencies.

As seen in the above diagram of an airplane transponder the reply button illuminates when you reply to the wave received from the interrogator. The mode of the operation is controlled by selecting the on or off buttonon the left side of the above diagram.
When the ID button is pressed called the IDENT button it flashed for a few seconds on the radar allowing the controller to establish positive connection with the aircraft. Test button checks for the proper working of the transponder. 1200 above displays transponder code given to the aircraft. It acts like a personal identification of the aircraft that is displayed on the radar of the ATC controller. In India, if the ATC controller does not specify any code then it is by default set as 2000, and in USA the default code is 1200.

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4

The direction and coordination of instrument flight rules (IFR) traffic within specific terminal areas is delegated to airport surveillance radar (ASR) facilities. Arrival and departure of the plane is all within the control of the ASR. This radar system only provided short range coverage of the airport area. Airport surveillance radar systems are capable of reliably detecting and tracking aircraft at altitudes below 25,000 feet (7,620 meters) and within 40 to 60 nautical miles (75 to 110 km) of their airport. Most ASR utilise a form of automated radar terminal system (ARTS). This system has several different configurations which depend on the computer equipment and software programme used. Usually the busiest airports have the most sophisticated computers and program used. This system is installed with a suffix of numbers and letters, for example: ARTS-111A.

Installation can detect, track and predict primary as well as secondary radar returns. On the controllers radar screen ARTS equipment automatically provides a continuous display of the aircrafts position, altitude, speed, and other information pertaining it. This information is updated continuously as the aircraft progresses through the terminal area. 

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5

When you are using the radio it is important to speak in a professional manner which ensures that others understand the message you are trying to convey. Slang, jargon and incorrect radio procedures should be corrected immediately or else it can compromise on the safety of yours and of others. Your first and most important lesson as you learn to use the right words is not be afraid of using the wrong words.

Regardless of the form it takes, communication is the goal. As you learn aviation's language, your vocabulary and phraseology will improve, so relax and communicate. Radio transmission should be as short as possible in order to keep the radio frequency less congested.  If the controller is working five other airplanes and needs to issue timely control instructions, he can't do it until you release the microphone button. This delay may affect the safety of the other airplanes. Transmissions that are too brief usually result in the controller asking you to provide more detail. 

When you are ready to speak on the mike you should know well in your mind what you want to speak and before you speak you should pause for a few seconds to know whether someone else is talking on the phone or not. When you talk you should tell who you are, where you are and what you are requesting for. When you are ready to speak, hold the mike close to your lips and speak in a very clear and normal tone. If you do not receive any response then you should try again. Also you should check that the mike is not stuck at the transmitting position as if so then it can block the other transmissions and disrupt communication with others for a long period of time. 

If your airplane has an intercom, connecting a tape recorder to it, that is an easy way to take notes of ATC communications. It allows you to replay the transmissions you didn't get on the first pass, and it gives you a chance to review how well you used the right words during your flight. You can also listen to ATC communications at your leisure. You can increase how fast you hear, and improve what you understand, if you know what to expect during a transmission. ATC instructions mostly consist of numbers preceded by key words that tell you what the numbers mean. For example, "climb and maintain...." is always followed by an altitude assignment. Controllers frequently combine the three words into one—"climbandmaintain" but they're more deliberate with the altitude assignment, such as "one-two-thousand." An experienced pilot recognizes the word group and knows that an altitude follows. The Aeronautical Information Manual (AIM) is the best reference for learning good ATC communication skills and phraseology.

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6

When you transmit or receive numbers over the radio, each number is spoken the same way you are used to saying it, with the exception of the number nine. It is spoken as “niner” to distinguishit from the German word “nein” which means no. To reduce confusion, certain sets of numbers are spoken as individual digits. When you state radio frequencies, the decimal is pronounced as “point” but the decimal is dropped when you state an altimeter setting. In the U.S. each aircraft is identified by a registration number which is painted on the outside of the airplane. Registration numbers usually are a combination of five letters and numbers. They are sometimes referred to as the tail number, or N-number, because all U.S. registered aircraft have an N preceding the number. On the initial call ups to ATC or other facilities, you should state the number of facility you are calling and then give your aircraft type, model or manufacturer and registration number. If you state the manufacturers name or model you may drop the N prefix of the registration.

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7

Since a flight may cross several time zones, it would be confusing to estimate the arrival time at your destination using only the local time at the departure airport. To overcome this problem, the aviation uses the 24 hour clock system, along with an international standard called coordinated universal time (UTC). The 24 hour clock eliminates the need for a.m. and p.m. designations, since the 24 hours of the day are numbered consecutively. For instance, 9 a.m. becomes 0900hours, 1 p.m. becomes 1300 hours, and so on. Coordinated universal time, which is referred to as Zulu time in aviation, places the entire world on one time standard. When a given time is expressed in UTC, or Zulu, it is the time at the 0 degrees line of longitude which passes through Greenwich, England. All of the 24 time zones around the world are based on this reference. In the United States, you add hours to convert local time to Zulu time and, to convert Zulu time to Indian time, you subtract hours.

Coordinated Universal Time (UTC) is the basis for civil time in many places worldwide. Many ...
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8

The NATO phonetic alphabet, more accurately known as the International Radiotelephony Spelling Alphabet, and also called the ICAO phonetic or ICAO spelling alphabet, is the most widely used spelling alphabet. Although often called "phonetic alphabets", spelling alphabets do not have any association with phonetic transcription systems, such as the International Phonetic Alphabet. 

Instead, the International Civil Aviation Organisation (ICAO) alphabet assigned code words acrophonically to the letters of the English alphabet so that critical combinations of letters and numbers can be pronounced and understood by those who transmit and receive voice messages by radio or telephone regardless of their native
language or the presence of transmission static. It would be difficult for pilots to speak all of the language which could be involved in international flight. Thus the ICAO member states have agreed to make English language as the language for air/ground communication. 

When the pilot identifies the aircraft during initial contact with ATC or other facilities he will use the phonetic alphabet as a routine measure. Since letters like B, C, D, AND E have similar sounds they can be easily mistaken for one another especially during radio transmission. The phonetic alphabet was thus developed to avoid misunderstanding of this type.


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1. System used for communication by an aircraft
2. Live Flight Tracker Called Radar
3. Transponder Operation
4. ATC is Watching you - Airport Surveillance Radar
5. Using The Radio - ATC Communication
6. ATC Communication -Using Numbers on The Radio
7. Coordinated Universal Time
8. Phonetic Alphabets
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