Study Guide:Delivery

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Radio Communication - Basics

Because communication is crucially important for Air Traffic Control a fixed format and syntax is used, in order to minimize the risk of misunderstandings and to keep messages short. Worldwide English is the primary language in use, however in most countries you are also allowed to use the local language. In Austria VFR flights can choose their language whereas IFR flights are mostly conducted in English. Link: Buchstabiertabelle

Basic Rules

In order to achieve the goals set above the following rules important:

  1. Listen before you talk
    It's impossible for two radio stations to transmit on the same frequency at the same time. If this is done, the radio signal will be blocked and this will result in a nasty noise on the frequency. Therefore it's important that every station monitors the frequency for about 5 seconds before transmitting, to make sure there’s no ongoing radio traffic. If you hear an ongoing conversation, wait until the conversation is over before you begin to transmit. Don’t start your communication if there is a read-back expected on the last transmission even if there is a short pause.
  2. Think before you talk
    The radio traffic flow should be as smooth as possible. To achieve this it's vital to "think first" before transmitting so that a clear, concise and uninterrupted message can be sent.
  3. As far as possible use standard phraseology and syntax
    To prevent misunderstandings and to maintain the radio traffic as effective as possible, stick to standardized phraseology and skip slang and of course private messages.

Callsigns and Initial Contact

Every participant on the network has his own Callsign. Controller Positions are identified by their location and their Function (e.g. Wien Radar, Graz Tower), Aircraft either by their Registration (e.g. OE-ALB) or an Airline Callsign followed by a combination of numbers and letters (e.g. AUA25LM, SWR387). To pronounce these letters and digits the ICAO-Alphabet is used. To initiate the contact between two stations an initial call has to be made. This call has the following structure:

Station 1: Station 2, Station 1, Message 
Station 2: Station 1, Station 2, Message

Example - Austrian 251 is calling Wien Tower:

AUA251: Wien Delivery, Austrian 251, Radiocheck 
LOWW_DEL: Austrian 251, Wien Delivery, read you 5 by 5

In Subsequent calls the calling station part can be ommited.
When a controller (or aircraft) transmits a message to a station it is very important that the receiving station acknowledge the message and reads back any required parts.. If the receiving station does not acknowledge, the transmitted message is considered as a lost transmission and the sender should resend the message or check if the receiving station got the message. Items that must always be read back in full are all clearances (including altitudes, headings, speeds, radials etc), runway in use, altimeter setting (QNH or QFE) and transition level, and all frequencies. For a controller, this is extremely important to remember, since if a pilot's readback is incorrect, the controller has to ask for confirmation, i.e a new readback. There are also items that should not be read back to reduce unnesessary radio transmissions. In short, this includes everything not mentioned above, but a few examples are: wind, temperature and other weather information (except altimeter settings) and traffic information in detail. When giving an instruction the Callsign is stated at the beginning, when reading back you usually add it at the end of your transmission (although you are allowed to do it at the beginning too).


LOWW_APP: AUA251, turn left heading 290, descend Altitude 5000 feet, QNH 1019.
AUA251: Turn left heading 290, descending altitude 5000 feet QNH 1019, AUA251 

LOWW_GND: OE-DLT, taxi to Holding Point Runway 29 via Exit 12, M and A1, QNH 1019, give way
to Speedbird Airbus A320 crossing you right to left on M.
OE-DLT: Taxiing to H/P Rwy 29 via Exit 12, M and A1, giving way to Speedbird
Airbus A320 on M, OE-DLT.


References for detailed information: METAR, TAF 

How is an Aerodrome organized

As airports grew bigger over time also the workload for the Air Traffic Controller handling the traffic got bigger. Soon it was necessary to distribute this workload onto more than one controller in order to be able to cope with the traffic.

So the Tower Position got divided into thre basic types with different areas of responsibility.

  1. Clearance delivery (DEL), responsible for checking flightplans and issuing IFR clearances to departing aircraft.
  2. Ground (GND), responsible for all traffic on the apron and the taxiways.
  3. Tower (TWR), responsible for movements on the runway and within its associated Control Zone.

Because Tower and Ground controllers rely very strongly on what they see out of their window, these are the positions which are situated within the airports control tower.

Apart from that there are the controllers who manage the traffic once it has left the control zone. They are again divided into:

  1. APP Positions, managing the traffic within the airports vicinity (the so called TMA, Terminal Area). In Austria they are situated directly at the airports.
  2. ACC (Area Control Center, on VATSIM the abbreviation CTR is used) positions, which are responsible for enroute traffic. They reside in Vienna.
  • Since they all use their radar to control air traffic, they are also called Radar positions.

Working Delivery Positions


Flightplan Structure


Aircraft routing types used in flight planning are: Airway, Navaid and Direct. A route may be composed of segments of different routing types.

  3. Direct: Direct routing occurs when one or both of the route segment endpoints are at a latitude/longitude which is not located at a Navaid. This is a routing from Vienna

Issuing IFR Routing Clearances


Destination of flight
Initial climb altitude after departure (5000ft)
Squawk (Squawk assignments for LOWW are 4600 to 4620)
QNH (Local QNH of airport according to latest METAR) = given with taxi clearance


Normal construction of a routing clearance:



Squawk 4601.


Squawk 46XX




Callsign, readback correct. Austrian 125, readback correct /(readback was correct)


Special Situations (High Traffic, Slots, ...)



Behavior in situations with increased traffic


If possible you should inform the pilot about the expected delay:

Austrian 125, readback correct, expect startup in 10 minutes.
Austrian 125, startup approved, expect departure in 10 minutes.