This study guide is still work in progress. Stay tuned for further chapters.
This Study Guide is designed to give you all the information you need to become an efficient Tower Controller within VACC Austria. We assume that you have already read the Study Guide:OBS, Study Guide:Delivery and Study Guide:Ground.
Tower's main responsibility is to make efficient use of all available RWY's.
The tower is therefore responsible:
- for all movements on the runways - for all movements within the control zone (see "Airspace Structure" below).
Euroscope visibility range for Tower should not exceed 50nm (regarding Vatsim CoC C12)
A/C are categorized by their respective weight and approach IAS
Aircraft are categorized into four weight categories:
|Light Aircraft (L)||< 7 000 kg|
|Medium Aircraft (M)||7 000 – 136 000 kg|
|Heavy Aircraft (H)||>136 000 kg|
|Super Aircraft (S)||is only one: the A380|
You can find a list of aircraft in this link 
Weight depicted is MTOW.
Aircraft are categorized by their reference approach speed (Vref) at maximum landing weight:
|A||<= 90 knots|
|B||91 - 120 knots|
|C||121 - 140 knots|
|D||141 - 165 knots|
|E||>= 165 knots|
For an aircraft to fly the lift force produced by (mostly) the wings has to outweigh the gravitational force that affects the aircraft.
Basically, a wing produces lift by deflecting the air it moves through into one direction. According to Newton's third law of motion, the lift is produced in the opposite direction. This lift grows with the speed the aircraft has in relation to the air and with the angle, the wing draws with the direction of movement. This angle is called Angle of Attack (AoA).
The principle only works as long as a steady airflow around the wing exists. As soon as the airflow seperates from the wings surface the lift starts to decrease. The AoA at which this occurs is called critical Angle of Attack. It depends on the profile of the wing and it's dimensions but for subsonic aircraft, it typically lies between 8 and 21 degrees.
Think of a level flying aircraft that reduces its speed. In order to compensate for the reducing lift, the pilot has to raise the nose. However, at some point, the Angle of Attack will cross the critical angle of attack and the pilot will find himself in a stall. So the speed of an aircraft is limited on the lower side by the so-called stall speed but the aircraft is also limit by aerodynamics in the higher range of speed (buffeting). Because the stall speed depends on the profile most aircraft are equipped with devices that alter the profile during flight such as flaps or slats (Approach). In General, when an aircraft flies it will produce thrust but at the same time it produces drag. So if you fly just horizontal (cruise) you have at the same time Lift=weight and thrust=drag. Drag produce automatic noise and that is the big problem. to prevent this we have different procedures in the approach and a lot of research in aviation to reduce the sound of the aircraft but the main part are the engines.
On approach, pilots have to fly in a certain speed range in order to conduct a safe landing. The lower boundary is called landing reference speed and is often a fixed multiple of the stall speed. As a result of this, the approach speed also depends on the weight and aircraft configuration (Flap/Slat setting). For safety, the Approach Vapp is higher than Vref and the difference depends mostly on the weather conditions.
Generally, you can say that bigger aircraft also have a bigger approach speed however at some point this rule does not work anymore because the Vref depends largely on the aircraft's weight in relation to its maximum takeoff weight (MTOW). The speed ranges from 50 knots in a C150 up to 170 knots with a fully loaded 747. However for example it is possible that a light 747 is slower than a fully loaded 737.
Transition Altitude/Transition Level
Aircraft Altimeters use the air pressure around them to determine their actual altitude. In order to get correct readings, you have to use the actual local pressure in your area. As a memory hook, you can use this: The altimeter needle moves in the same direction you turn the rotary knob to adjust the pressure. If you turn it counterclockwise, the needle also turns counterclockwise and therefore indicates a lower altitude.
As ground pressure changes every hundred miles, aircraft would need to update their settings every few minutes. If ALL aircraft would need to do this, it would be terribly unpractical and dangerous. Guess what happens if one forgets? So the altitude is "sliced":
- In lower areas (where the terrain is in close proximity), aircraft have to update local settings. Most aircraft are there only for takeoff and landing, so no big deal.
- In higher areas, aircraft all tune a standard-setting (QNH 1013 or 29.92 HG) - this setting may be "wrong", but as all aircraft have the same "wrong" setting, it does not matter.
And where is the altitude where that changes?
- For climbing aircraft, it is the Transition Altitude, where they change from local to standard pressure.
- For descending aircraft, it is the Transition Level, where they change from standard to local pressure.
Between the two, there is a safety layer (called "Transition Layer") which compensates for the difference between local and standard pressure, which is 1000ft minimum, so the stack is:
Upper airspace: measured in Flight Levels (FL220 = Altitude 22.000ft at standard settings) Transition Level: the lowest Flight Level Transition layer (to keep distance) Transition Altitude (TA): the highest altitude cleared at local pressure settings Lower airspace, where the altitude is given (you write "A5000ft").
As the difference between TA and TL varies with pressure (the lower local pressure, the thinner), the size of the Transition Layer varies (the lower local pressure, the thicker). Use the following table to calculate your TRL:
QNH < 0977: TA + 3000 ft. QNH 0978 - 1013: TA + 2000 ft. QNH 1014 - 1050: TA + 1000 ft. QNH 1051 > : TA = TL
Before you start controlling
Tower decides which runways are in use and maintains the ATIS. The tower is also responsible for ground and delivery if they are not online or if they are not defined for that particular airport (LOWS has DEL, but no GND; LOWI, LOWG and LOWK have only TWR).
Airspace Structure around Major Airports
Major airports in Austria are surrounded by a control zone (CTR) which is class D airspace. This means that A/C need clearance for entry. So either they are cleared for an approach or they are cleared into the control zone. Details will be discussed in the VFR part later on.
Setting the right priorities
The moment you are responsible for more than one aircraft you will have to set priorities in your handling. As a general guideline:
- aircraft in the air have top priority - you take care of them first. Reason: They can't stop.
- aircraft moving on the ground have next priority. They could bump into each other.
- aircraft standing on ground have the least priority.
The runways are one of the most dynamic spots on an airport. Aircraft are travelling at high speed with little room to manoeuvre and most of the time no ability to stop at a reasonable distance. In general only one aircraft may be cleared to use a runway at the same time., nevertheless there are exceptions to this rule which will be described in the upcoming chapters.
So now we are at the point where the pilot reaches the Holding Point of his departure runway and reports ready for departure. What are the things you should check before issuing the takeoff clearance?
- Have a look at the Flightplan. Take note of the type of aircraft and the Departure Route.
- Check the traffic approaching the runway.
To give a takeoff clearance the following phrase should be used:
AUA2CM, wind 320 degrees, 7 knots, Runway 29, cleared for takeoff.
When the A/C is well established in climb check if squawking Mode C and the right Code. Afterwards, he is handed off to the next Controller, in this case, a radar position:
AUA2CM, contact Wien Radar frequency 134.675.
The next aircraft reports ready for departure. Again check the points above, but this time we cannot give the takeoff clearance straight away because the preceding aircraft is still occupying the runway. Now you get to know the first exception to the Runway separation rule above. To speed things up you can instruct the next aircraft to line up behind the first one while this one is still in the takeoff roll occupying the runway:
AZA639, behind departing Austrian Airbus A319, line-up rwy 29 behind.
Note: you must add another "behind" at the end of the clearance!!
This type of clearance is called conditional clearance.
The earliest possible point where you can issue the next takeoff clearance is, when the Proceedings aircraft has overflown the opposite runway end or has clearly turned onto either side of it.
Take care! Phraseology around the runway is vital
In 1977, at the Tenerife Airport, two 747 Jumbo Jets collided on the runway and burst up in flames, killing more than 500 people. There was a simple cause: misunderstandings in the takeoff phraseology: Tower said "standby for takeoff", the pilot understood "cleared for takeoff". So, there are two iron rules which you should never break as a Tower controller:
- Use the word "takeoff" only when you clear for takeoff: Say "<aircraft> cleared for takeoff" and nothing else. If you have to say anything else (like that the aircraft can leave in 2 minutes), then use the word "departure".
- Use the word "landing" only when you clear for landing: Say "<aircraft> cleared to land" and nothing else. If you have to say anything else (like where to leave the runway after touchdown), use the word "arrival".
There are several factors to take into consideration when deciding what the minimum separation between succeeding aircraft is. It is the tower controller's responsibility to decide which kind of separation to apply. The following types of separation shall be considered:
CAUTION: Regardless of separation minima to be used, the following rule ALWAYS applies:
Departing aircraft will not normally be permitted to commence take-off until
- the preceding departing aircraft has crossed the end of the runway-in-use or
- has started a turn or
- until all preceding landing aircraft are clear of the runway-in-use.
Note that this paragraph is not about the actual clearance. You may clear an aircraft - considering the minima below - for takeoff before the above conditions are fulfilled, taking into account the time it will take the aircraft, until the actual takeoff can be commenced.
Time Based Separation
To avoid hazards created by the turbulence formed at the wingtips of aircraft (wakes), separation based on time shall be applied between succeeding departing traffic. This is due to the fact, that wakes need a certain time to dissipate.
The actual time to apply depends on the wake turbulence category and thus on the weight of the aircraft:
|Light Aircraft (L)||< 7 000 kg|
|Medium Aircraft (M)||7 000 – 136 000 kg|
|Heavy Aircraft (H)||>136 000 kg|
Provided that succeeding aircraft are using:
- the same runway
- crossing runways if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 300 m (1 000 ft) below
- parallel runways separated by less than 760m (no applicable in Austria)
- parallel runways separated by 760 m (2 500 ft) or more, if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 300 m (1 000 ft) below (not applicable in Austria)
a minimum separation of 2 minutes applies whenever a
|Light or Medium||follows||Heavy|
Provided that succeeding aircraft are taking off from:
- an intermediate part of the same runway (read: intersection)
- an intermediate part of a parallel runway separated by less than 760 m (2 500 ft) (not applicable in Austria)
a minimum separation of 3 minutes applies whenever a
|Light or Medium||follows||Heavy|
Note: In LOWW the following intersections are, for the purposes of wake vortex, NOT considered to be intersection departures:
|11||A11 and A12|
|29||A1, A2 and A3|
|16||B1 and B2|
|34||B11 and B12|
To point out this hazard to a pilot the following phrase should be used:
DLH32C, wind 180 degrees, 3 knots, runway 16 cleared for takeoff, caution wake turbulence.
For radar-equipped TWR stations, which in Austria are basically all controlled TWR stations, departure separation shall be as such, that departing aircraft are entering the approach airspace with radar separation. For LOWW_TWR these minima are for example:
|Departing traffic on different SIDs||3 nm||increasing|
|Departing traffic on same SIDs||5 nm||increasing|
Note: LUGEM and MEDIX count as the same SID
Deciding Which Separation to apply
In order to provide an expeditious flow of traffic for departing traffic, it is imperative for the tower controller to always apply the lowest separation minimum. Since time-based separation is always the larger of the minima, it should always be strived to achieve radar separation. In principle, taking the minima above into consideration, radar separation may always be applied when succeeding departing traffic is in the same wake turbulence category or if a heavier aircraft is departing behind a lighter one. Otherwise, time based separation has to be applied.
Tips And Tricks
- Try to avoid having multiple aircraft using the same SID depart the same runway right after each other. Throw in a departure with another SID in between to utilize the 3nm radar separation minimum instead of 5.
- If possible, have heavier planes depart behind lighter ones, so you avoid having to use time-based separation. Of course, take this with a grain of salt, since you can't let the heavier aircraft wait forever.
- To achieve radar separation as soon as possible, use initial visual turns if weather permits (VMC). Example:
TWR: AUA117M, after departure visual right turn to SOVIL is approved, wind calm, runway 11 cleared for takeoff.
In this case, the aircraft will make a very early right turn, allowing you to have the next aircraft takeoff within seconds, provided it is not lighter than the preceding.
- The ground controller should send aircraft to your frequency early enough during taxi - provided that there are no conflicts on the ground - that you should be able to distribute the aircraft onto the different holding points to your needs. Use the holding points in order to prepare a proper departure sequence that allows you to use the lowest minima possible.
Note: According to the austrian AIP, the pilot shall prepare and be ready to use the following intersections for departure:
For those intersections it is normally not necessary to ask a pilot if he is able - it is his obligation to tell ground upon requesting taxi clearance or latest upon initial contact with the tower controller.
Arriving Aircraft call you when they are established on an approach to a runway. Most of the time this is an ILS Approach but also other kinds are possible.
MAH224: Linz Tower, MAH224 established ILS Approach rwy 27.
Again you are not allowed to clear more than one aircraft onto the same runway at the same time.
|In order to issue a landing clearance
If these conditions are met use the following phrase to clear the aircraft:
MAH224, Linz Tower, wind 300 degrees 16 knots, runway 27, cleared to land.
During periods of high traffic, it is likely that you have more than one aircraft approaching the same runway at the same time. The approach has to ensure the minimum radar separation of 3 nm and additionally increased separation due to wake turbulence.
AUA26T: Linz Tower, AUA26T established ILS 27. TWR: AUA26T, Linz Tower, continue approach, wind 300 degrees 16 knots.
|Meanwhile MAH224 has left the runway.|
AUA26T wind 310 degrees 14 knots, runway 27 cleared to land.
|AUA81 is approaching runway 16, OE-AGA is on left base runway 16 and there is a rescue helicopter operating in the area around Freudenau.|
AUA81: Wien Tower, AUA81 established ILS 16 TWR: AUA81, Wien Tower, VFR traffic is on left base rwy 16, continue approach, wind 140 degrees 7 knots. AUA81: continuing approach, AUA81. TWR: AUA81, There is a rescue helicopter operating west of the extended centerline, presently at your one o'clock position, 5 nm, 1400 ft. AUA81: Thank you, looking out, AUA81. AUA81: traffic in sight, AUA81.
Helicopters don't need a Runway for the approach, sometimes they are able to land at their parking position, lets have a look on the Phrases.
The rescue helicopter from the example above needs to land at your airport: OEBXR: Wien Tower, Freudenau 1500ft for landing. TWR: OEBXR, Fly direct G-A-C, stay north of extended centerline RWY 11, 020 deg 4 kts, land own discretion.
To give you an idea of how dense traffic can get in real life consider that during peak times and good weather the separation is reduced to 2,5 nm. This corresponds to one landing every 75 seconds.
Merging Departing and Arriving Traffic
And now to the most fun part of being a Tower Controller. Sometimes you get into the situation that you use the same runway for departures and arrivals. Either your airport has only one runway or weather demand this configuration.
Still the above rule of only one aircraft at the same time applies, however, we also use conditional clearances which look very similar to those above in the departing traffic section.
AUA123, behind next landing C750 line up RWY 29 behind.
To depart an aircraft in front of an approaching aircraft at the time of the departure clearance given the arriving aircraft should not be closer than 4 nm to touchdown. To squeeze a departing aircraft between two arrivals you normally need a minimum of 6 nm between them. It is important for you to check carefully if you have the necessary gap, so have a close look at the distance between the arrivals and their speed. If the second one comes in faster than normal consider this in your calculation. Also, you should make sure, that the pilot will be ready for departure when you need him to depart. To check this use the following phrase:
"Ready for immediate departure?"
|You are the Tower Controller at Vienna airport. Runway 29 is active for departures and arrivals. One aircraft is on a 5 nm final, one at 12 nm out. Additionally, you have two departures waiting at the holding point of runway 29.|
TWR: CAL275, ready for immediate departure? CAL275: Affirm TWR: Wind 250 deg 6 kts, Runway 29 cleared for immediate takeoff. CAL275: cleared for immediate takeoff runway 29, CAL275
|After the CAL B747 has taken off.|
TWR: AUA289, wind 300 degrees 7 knots, runway 29, cleared to land. AUA289: Runway 29, cleared to land, AUA289. TWR: AUA2LT, behind landing Airbus line up runway 29 behind. AUA2LT: Behind the landing Airbus, lining up runway 29 behind, AUA2LT.
|AUA289 has vacated the runway.|
TWR: AUA2LT, wind 300 degrees 8 knots, runway 29 cleared for takeoff. AUA2LT: cleared for takeoff runway 29, AUA2LT.
Differences to handling of IFR Traffic
The essential collision safety principle guiding the VFR pilot is "see and avoid." Pilots flying under VFR assume responsibility for their separation from all other aircraft and are generally not assigned routes or altitudes by air traffic control. Governing agencies establish specific requirements for VFR flight, consisting of minimum visibility, distance from clouds, and altitude to ensure that aircraft operating under VFR can be seen from a sufficient distance to ensure safety.
To guide VFR Traffic through your airspace you make use of VFR Routes, Sectors, and reporting Points. Used phrases:
TWR:OE-AGA, enter control zone via VFR route Klosterneuburg, 1500ft or below, QNH 1020, Squawk 7000, report XXXX (i.e. Freudenau), expect runway 29. TWR:OE-AGA hold (orbit) overhead XXXX (i.e. Freudenau) in XXXX (i.e. 2500ft)
VFR flights should be guided into downwind, base and final leg for landing.
TWR: OE-AGA, join downwind for runway 29 TWR: OE-AGA, join base for runway 29
VFR Flights Squawk and basic information (active runway, QNH etc.) from Delivery, the route clearance from Tower. After startup, they will contact Ground for taxi, thereafter the Tower will issue the clearance. A possible VFR clearance could be:
TWR:OE-AGA, verlassen Sie die Kontrollzone über Sichtflugstrecke Klosterneuburg, 1500 Fuß oder darunter, QNH 1014, Squawk 7000, Rechtskurve genehmigt. TWR:OE-AGA, leave Control Zone via VFR-route Klosterneuburg, 1500 feet or below, QNH 1014, Squawk 7000, right turn approved.
TWR: OE-AGA, steigen sie auf 3500 Fuß, melden Sie Donauturm. TWR: OE-AGA, climb 3500 feet, report Donauturm.
In the air ATC provides traffic information.
TWR:OE-AGA, Traffic at your 12 o'clock position, 2100 feet, a PA28 on VFR inbound route Klosterneuburg-Freudenau.
When the aircraft leaves the control zone.
TWR: OE-AGA, Squawk 7000, you may leave.
Wien Tower/Turm can also be contacted in German.
Merging in VFR Traffic
To manage VFR Traffic efficiently you have to use traffic information and visual separation.
TWR: OE-ANX, traffic at your 3 o´clock position, moving right to left, B767, distance 2.5 miles, report mentioned traffic in sight OE-ANX: Traffic in sight, OE-ANX
Because of other traffic, it might be necessary for the aircraft to remain in the downwind leg until the traffic has passed:
TWR: OE-AGA, Extend right downwind. OE-AGA: Extending right downwind, OE-AGA
To instruct the aircraft to continue it's approach use the following procedure:
TWR: OE-ANX, traffic at your 3 o´clock position, moving right to left, B767, distance 2.5 miles, report mentioned traffic in sight OE-ANX: Traffic in sight, OE-ANX TWR: OE-AGA, behind B767 traffic, join final RWY 29, caution wake turbulence OE-AGA: Behind B767, join final RWY 29 behind, caution wake turbulence, OE-ANX
When using an extended downwind you should always consider that the aircraft's speed might be considerably lower than the speed of other aircraft involved. So if an aircraft has to fly a long way out it might take some time for it to come all the way back, generating a big gap in the arrival sequence. Instead, you should aim to keep the plane within the vicinity of the airfield:
TWR: OE-AGA, Make a right three-sixty. OE-AGA: Making three-sixty to the right. TWR: OE-AGA, Orbit left OE-AGA: Orbiting left, OE-AGA
The second instructions mean, that the pilot should make orbits until further advice.
It is also possible to ask VFR traffic for a speed reduction.
TWR: OEABW, Fly speed 90 kts OEABW: 90 kts, OEABW
Could be used when weather Minimums are below VFR condition.
Weather minimums for (S)VFR are follow
- Base Cloud at min. 600ft
- visibility min 1500m
Verlassen Sie Kontrollzone als Sonder-Sichtflug über Donauroute. Verlassen Sie Kontrollzone als Sonder-Sichtflug. Nach dem Abheben geradeaus steigen auf 600 ft, dann Rechtskurve Steuerkurs 340. Verlassen Sie Kontrollzone als Sonder-Sichtflug. Nach dem Abheben geradeaus bis zur Ende der Raffinerie. Folgen Sie der Donau. Ausflug Richtung Norden genehmigt.
Leave control zone special-VFR via November Leave control zone special-VFR. After departure climb on runway heading 600 ft then right turn heading 340 Leave control zone special-VFR. After departure climb on runway heading until end of refinery. turn right heading 360, follow the Danube. Leaving control zone to the north approved.
Night VFR is handled like any other VFR flight. Adherence to special procedures associated with flying VFR after ECET and clearance of terrain is the responsibility of the PIC.
The traffic pattern is separated into departure, crosswind, downwind, base, and final. On request, the Tower controller can clear VFR traffic into the traffic pattern.
OEABC, after departure, join traffic pattern Runway 29.
OEABC, after departure, join downwind runway 29.
If the controller clears an aircraft into any part of the pattern, it implies the clearance for the whole pattern. To tell the pilot to maintain on the downwind use:
OEABC, extend downwind
OEABC, I call you for base
Helicopters are sometimes able to depart from their current position i.e helipad, GAC, TWY. Nevertheless they may also depart via runways:
OEBXR: Wien Tower, OEBXR at G-A-C request to leave the Control Zone via Klosterneuburg. TWR: OEBXR, Wien Tower, after departure leave control zone via VFR Route Klosterneuburg, 1500 feet or below, SQ7000. OEBXR: After departure leave control zone via VFR Route Klosterneuburg, 1500 ft or below, SQ7000. TWR: Correct, ready for departure? OEBXR: Affirm TWR: 260 deg 4 kts, Takeoff own discretion. TWR: Airborn Time 52'
Coordination with other ATC Stations
Communication from one controller to another is as important as the communication from controller to pilot. This is especially true during high traffic situations where you might be tempted to concentrate solely on what is happening on your frequency. In these situations don't hesitate to take a call from a fellow controller even if it means that a pilot has to wait before you call him back. Secondly, if you know a controller is busy, try to keep your conversation with him concisely and avoid chatting in a TeamSpeak channel next to him.
Within VACC Austria we usually use TeamSpeak to coordinate with each other. The coordination with other ATC units is mostly done per private chat. Other means of communication are the Intercom functions of Euroscope which would be a very nice feature, however often they only work with certain controllers. The ATC Channel within Euroscope should not be used for individual coordination.
When you come online or go offline you should inform neighbouring ATC stations.
Special Situations (High Traffic, Slots, ...)
Reduced Runway Separation Minima (LOWW)
Each runway in Vienna has a 2400m-marker indicated on the runway - be aware that the second marker from the respective threshold is the 2400m-marker for that very threshold: For details refer to ICAO DOC4444 7.11
Application of RRSM: An aircraft may be cleared for takeoff, given that:
- a preceding departing aircraft has passed the 2400m-marker.
An aircraft may be cleared to land, given that:
- a preceding landing aircraft has passed the 2400m-marker, is in motion and is not required to make a backtrack.
- a preceding departing aircraft has passed the 2400m-marker.
Reduced runway separation minima shall be subject to the following conditions:
- wake turbulence separation minima shall be applied
- visibility shall be at least 5 km and ceiling (BKN/OVC) shall not be lower than 1000ft.
- tailwind component shall not exceed 5 kt
- minimum separation continues to exist between two departing aircraft immediately after take-off of the second aircraft
- traffic information shall be provided to the flight crew of the succeeding aircraft concerned
- Reduced runway separation minima shall not apply between a departing aircraft and a preceding landing aircraft
- Reduced runway separation minima shall only be applied during the hours of daylight from 30 minutes after local sunrise to 30 minutes before local sunset. (simplified VATSIM rule: once night-SIDs are in operation, RRSM is not applicable anymore)
High traffic situations
During high traffic situations, communication with adjacent approach sectors is very important. Especially during single runway operations you might have to ask for increased inbound spacing to be able to fit in departing aircraft.
Additional phrases during periods of high traffic
In order to expedite the flow of traffic use the following phrases:
Austrian 125, wind xxx/xx runway 29 cleared for takeoff, expedite Austrian 125, wind xxx/xx runway 34 cleared to land, expedite vacating OE-ABC, wind xxx/xx, runway 29 cleared for takeoff, after departure right turn
Opposite runway operations
This is one of the more difficult situations for a Tower controller. You have to consider the departure route of each aircraft to estimate the required spacing to arriving traffic. Again close coordination with approach is very important.
If you really want to study hard, then read the relevant sections for DEL in the official radio telephony guide from Austrocontrol.
A really good index (and much more orderly is here at Eurocontrol.