This study guide is still work in progress. Stay tuned for further chapters.
- 1 Introduction
- 2 Radio Communication - Basics
- 3 METAR and TAF
- 4 How is an Aerodrome organized
- 5 Working Delivery Positions
This Study Guide has been designed to give you all the information needed to start controlling as a Clearance/Delivery controller on the VATSIM network.
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
In order to achieve the goals set above the following rules important:
- 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.
- 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.
- 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.
LOWW_TWR: NLY2678, wind 330 degrees, 6 knots, Rwy 29, cleared for takeoff. NLY2678: Rwy 29, cleared for takeoff, NLY2678.
METAR and 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.
- Clearance delivery (DEL), responsible for checking flightplans and issuing IFR clearances to departing aircraft.
- Ground (GND), responsible for all traffic on the apron and the taxiways.
- 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:
- APP Positions, managing the traffic within the airports vicinity (the so called TMA, Terminal Area). In Austria they are situated directly at the airports.
- 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
Clearance Delivery is responsible for checking and correcting flightplans of departing aircraft and issue routing clearances to them.
Flight plans are documents filed by pilots with the local Civil Aviation Authority prior to departure. They generally include basic information such as departure and arrival points, estimated time en route, alternate airports in case of bad weather, type of flight (whether instrument flight rules or visual flight rules), pilot's name and number of people on board.
For IFR flights, flight plans are used by air traffic control to initiate tracking and routing services. For VFR flights, their only purpose is to provide needed information should search and rescue operations be required.
Aircraft routing types used in flight planning are: Airway, Navaid and Direct. A route may be composed of segments of different routing types.
- Airway: Airway routing occurs along pre-defined pathways called Airways. Mostly aircraft are required to fly airways between the departure and destination airports. The rules cover altitude, airspeed, and requirements for entering and leaving the airway (SIDs and STARs).
- Navaid: Navaid routing occurs between Navaids (short for Navigational Aids) which are not always connected by airways. Navaid routing is typically only allowed in the continental U.S. If a flight plan specifies Navaid routing between two Navaids which are connected via an airway, the rules for that particular airway must be followed as if the aircraft was flying Airway routing between those two Navaids. Allowable altitudes are covered in Flight Levels.
- 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
DEL gives routing clearances to all departing aircraft with the following information:
Destination of flight SID (= Standard instrument departure) Normally the filed SID is given 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 CTOT (= Calculated take-off time) Slot time (Normally not used on the VATSIM network)
The bold marked points are mandatory, all other points are optional.
Normal construction of a routing clearance:
Callsign, cleared to XXXX via XXXXX XX departure, (initial climb 5000ft), Squawk 46XX
Austrian 125, cleared to Frankfurt via LUGIM 1C departure, initial climb 5000ft, Squawk 4601.
Some Aircraft are not able to follow SIDs for various reasons, most of the time due to missing equipment. In these cases you should issue a so called vectored departure. A vectored departure clearance includes the same components as a normal clearance but instead of the SID you issue instructions to be carried out after departure. In this case the initial climb altitude is mandatory.
Callsign,cleared to XXXX, after departure RWY XX, XXXXXXX, initial climb 5000ft, Squawk 46XX
Austrian 125, cleared to Frankfurt, after departure Runway 29, turn left heading 240 expect vectors to LUGIM, initial climb 5000 ft, Squawk 4601.
You can find the instructions for each Airport within the Study Guide:Airport Details If the pilot responds with a correct readback you should answer with the following phrase:
Callsign, readback correct. Austrian 125, readback correct /(readback was correct)
Afterwards you either hand the pilot over to GND or wait for his startup request, depending on local procedures.
Special Situations (High Traffic, Slots, ...)
In order to guarantee a safe flow of traffic and to minimize delays in the air so called slots are being used. A slot is a timeframe of five minutes before to ten minutes after the CTOT mentioned before. The aircraft has to depart within this timeframe from its departure airport. On the VATSIM network this system is only used on special occasions.
Behavior in situations with increased traffic
Sometimes one of your neighboring sectors has to stop accepting traffic. In these cases you should delay an aircrafts start-up clearance.
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.