|Air traffic control|
See Air Traffic Control for the main article about this subject.
Air Traffic Control is an agreed procedure and process which keeps the aircraft separated to ensure that they don't crash into each other or are affected by turbulence when passing through the same air space. The separation of planes taking off or landing at airports is three minutes. This allows the air to settle again. Pilots have used an analogy of calling the atmosphere soup as air and liquid has similar properties.
In order to be able to effectively and reliably communicate, ATC and pilots agree on a set of keywords and jargon. This may vary between regions and the like. English is the agreed language for internaltional flights.
|xxxx_GND||Ground Controller||Controls the movement of aircraft on the ground at an airport, however only the taxiways and bays... not the active runways. Whenever a plane needs to cross an active runway, it has to call the tower.|
|xxxx_TWR||Tower Controller||'Owns' the runways and the airspace up to 10 NM (nautical miles) from the airport. Clears planes for takeoff and landing.|
|xxxx_APP||Approach Controller||Controls the airspace up to 30NM away from the airport, up to 18,000 ft (usually). Handles all aircraft leaving or arriving at an airport, until they are established on the ILS (then gives the plane to TWR) or are leaving their airspace to continue flight (then hands off to CTR)|
|xxxx_DEP||Departure Controller||An position rarely used except at busy airports in the real world which relieves the work-load of the approach controller by handling all the departures, and getting them away from arrivals as quickly as possible, leaving the approach controller free to handle arrivals (the hard bit).|
|xxxx_CTR||(ARTCC) Center Controller||Centers own all airspace not controlled by APP or TWR. They control the plane while en route, and get it from X to Y safely, until it can be descended and given to the approach controller.|
|xxxx_FSS||Flight Service Station||Flight Service Stations cover large areas (e.g.: France) and provide support to pilots and controllers. They can advise pilots of weather and frequencies for other controllers. They do not provide Air Traffic Control.|
|xxxx_DEL||Clearance Delivery||Clearance Delivery is rarely used in FlightSims. In the real world, a controller would give a clearance (which explains where the plane is allowed to fly) to all planes, but the ease of giving a clearance in the virtual world, means the Tower can normally give the clearance.|
The 'xxxx' in the table replace a code used to identify the area that controller is using. These are known as ICAO codes, and can be found on the ICAO web-site. For example, Heathrow is 'EGLL' so a Heathrow Tower Controller would log-in as EGLL_TWR.
Centers and flight service stations also have ICAO identifiers, but they are not for one airport, but for a larger area. For example, LFFF_CTR is France Center, and LFFF_FSS is the France Flight Service Station.
You may also see the callsigns xxxx_SUP and xxxx_OBS. These are used only in the virtual world and represent, respectively, a supervisor and an observer (someone who isn't controlling).
So now you can choose your position, but beware: if you are the approach controller at an airport which doesn't have a ground / tower controller, planes will expect you to offer them all those facilities, but if you are a London Center controller, you are not expected to offer center facilities to airplanes in an adjacent sector, but could be expected to offer very basic facilities of GND / TWR / APP to airports in your sector...
Now, we'll have a look at each of the positions in details:
Ground is possibly the easiest position available to controllers. The basic responsibility is to get planes to and from the runway and terminal buildings as quickly as possible (to save fuel and time) and to avoid planes colliding with each other. For this, you'll need a GROUND SECTOR FILE. These are very detailed maps of a particular airport (can be downloaded from the Sector System on IVAO) which hold all the taxiways as geographic data (press F5 to view).
Depending on the airport, the taxiways may have letters, or descriptions (e.g.: Inner Taxiway) or each section of the airport may have a number (called blocks). At Heathrow, the last two are used, so a statement like 'taxi to block 76 via the outer taxi-way' would be valid.
Tower has responsibility for all planes coming into or out of the airport, and the planes wishing to enter or cross the active runways. For Tower you can use any sector file with the airport shown, and center on your airport and zoom in to give your short (10NM) range. The first responsibility is to choose which runways to use (there's always at least 2 - one runway being used either direction) according to the weather (more later). You will also be expected to give IFR clearances, but this is very simple.
The biggest responsibility the tower has is to ensure that planes can take-off and land as quickly as possible, without any two colliding. Your approach controller should make sure that all planes arriving are well spaced and already heading directly for the runway. When a plane you've given permission to take-off to has left the ground, they are given straight to APP (Approach). Normally, there will not be a ground controller, so you may have to also give basic ground instructions (just ask a plane to get to the runway - not giving them directions - but warn them of any other traffic).
Approach is the most complicated position. Approach controllers deal with all traffic arriving and leaving (unless there is a departures controller - unusual). The main aim, as always, is to keep the aircraft arriving and leaving separated. For departing traffic, the aim is to get them going in the right direction and give them to center as soon as possible; for arriving traffic, the aim is to get them onto the approach (the correct height and heading) so that they can follow an electronic system (the ILS) which gives them exact guidance onto the runway, and then you can hand them off to the tower, who will clear them to land and try and get planes taking off in between the landings.
The difficulty is, of course, dealing with the high volumes of traffic around an airport. In Lesson 3, SIDs and STARs are introduced which are standard ways of leaving from or arriving at an airport which ensure that planes maintain separation.
An unusual position in the virtual world, the departure controller controls all planes leaving an airport; normally _APP will handle these but sometimes traffic means that there is just too much for a single controller to do. It is the aim of the departures controller to get the departing aircraft away from the airport as soon as possible without interfering with approach's planes. Later, you will see that departures are kept below a certain altitude until they're a distance away so that any arrivals can fly over them without any mid-air collisions.
In this position you absolutely must co-ordinate very closely with the approach controller.
_CTR (ARTCC - Center)
Center handles all airplanes in a specific area which are en route and not getting ready to land or having just departed. They navigate the plane from place to place as quickly as possible whilst ensuring that planes stay separated from each other. A plane may deal with many centers as it passes over many countries in a flight.
Notice how I've mentioned separation in every description? SEPARATION is the first key to controlling. It does not matter how far out its way a plane has to go if you keep everybody on board alive. A pilot may well want to have landed five minutes earlier, but it's your job as the controller to keep them separated. Of course, having said that, the second key to controlling is expedite flow - that is keep traffic moving quickly and get it where it wants to go by the most direct route.
Let's look at a plane taxiing to the runway and taking off now. So, to do this, we'll consider two controllers: ground control (_GND) and the tower (_TWR).
First, we have to know which runway is being used so that ground can get the plane to the right place. The rule is 'planes always like to be heading into the wind for takeoff or landing'. The winds are given in the METAR like 'xxxyy'. The direction of the wind is given first in 3 digits, and the speed after that in 2 digits; so 11007 indicates winds of 7kts with a direction of 110 (magnetic heading). Winds under 5 kts can be considered 'calm' and can be ignored. Thus, the basic idea is to match the heading of the wind, and the runway heading (add a '0' to the runway number - 17L is 170) as closely as possible. Runways are numbered by knocking the '0' off the heading, and appending 'L' for left or 'R' for right if there are parallel runways.
At Heathrow, there are runways 9L and 9R, and the same runways (used in opposite directions) 27R and 27L. If the wind is 110º @ 15 kts then runways 9L and 9R are most suitable, as 90 and 110 are only 20 degrees away, but 270 and 110 are 160º away! At Heathrow, where there are parallel runways, one runway can be used for landing and the other for taking off - so a plane can be leaving on 9L while another is almost landing on 9R. Where there is only one runway, the same runway can be used to landing and taking off. It is important to notice that if an aircraft is taking off on runway 7, and another lands shortly after on runway 7, they are travelling in the same direction, so they are not approaching each other, and a collision is impossible.
Knowing about your ATIS which can be read by all planes to avoid you repeating information, you would want to put the active runways in your ATIS so that other controllers know which runways you have chosen, and so planes have an idea of what they will be expected to do. Always keep your ATIS short (as it is hard for the pilots to read a long ATIS), and delete any blank lines at the end. The other component of your ATIS should be the current weather, so a good ATIS for a tower or ground controller would be:
London Heathrow Ground/Tower Information <alpha/bravo/charlie/delta/echo...>. Active runways are 9R for departures, and 9L for arrivals. Weather is (copy from METAR) 110@15 FEW030 OVC090 Q1015 NOSIG. On initial contact report you have <alpha/bravo/charlie/delta/echo...> ; the only detail to note here is the use of alpha/bravo, etc. Each time you update your ATIS change the identifier up by one, so start with alpha, then use bravo, then charlie. This is used so that when a plane calls you and says 'information alpha' you know if he has current information or an old version.
Now that the active runway has been established and the ATIS set-up, you can go about controlling. First, though, you need to know some basic guidelines about contact. Usually, expect a plane to call you first. They should give their current location, callsign (used to identify each plane) and which ATIS they have, so:
B-ELIO: Ground, this is B-ELIO at the terminal, Information Alpha. Request clearance to Paris Orly.
B-ELIO, a plane, has called you telling you where he is, what information he has, and what he wants. To reply, you need to tell him whether the information is current ('Alpha is current') or new information ('New active runway is 23') and reply to his request.
First, we earlier mentioned IFR clearance. This allows the controller to know where the plane is going, and to plan ahead for the aircraft. If you remember looking at a Flight Strip in lesson 1, you will recall it allows a controller to see the destination of the aircraft, the route the aircraft will follow and the requested altitude. The aim of the clearance is just to confirm these details with the pilot, especially in the real-world where they may be altered due to traffic levels, to make sure there aren't any mistakes and everyone knows what's going to happen. The clearance is as follows:
<Callsign> is cleared to <destination> as filed (give any changes to the flight plan here). After takeoff c/m (climb and maintain) <altitude> on runway heading / and turn <left/right> to <heading>, expect <requested flight level> after 10 minutes. Squawk <transponder code>.
Here's an example clearance:
You: B-ELIO is cleared to Paris Orly as filed. After takeoff c/m 6,000 and turn left to heading 180 (south) expect FL310 after 10 minutes. Squawk 5201.
The clearance can be given whilst on the ground, and is given by Clearance Delivery (_DEL) if one is online, else the GROUND (_GND), or TOWER (_TWR) controller. The pilot must read-back the whole clearance, to which you confirm by saying 'readback correct'. The Squawk code is a number used to identify the plane. It can be seen on the flight plan (will default to 1200) and means - in the real world - a controller can tell the dots apart as each one has a number. Just assign an available number in the 5000 or 6000 range (eg: 6001, 6002, 6003, etc.).
B-ELIO: B-ELIO cleared to Orly as filed. c/m 6000 left 180 - expect FL310 after 10, and squawk 5201.
You: B-ELIO, readback correct, call when ready to push-back and start-up.
B-ELIO: B-ELIO requests start-up and push-back.
Here a push-back and start-up means he wants a vehicle to pull the plane away from the buildings so he can start his engines... this is a real-world call, and is not used in the virtual world, so just approve it. He might skip this entirely and just ask if he can taxi, otherwise say:
You: Cleared to push-back and start engines. Call when ready to taxi
B-ELIO will then call you when he's ready to taxi. Note you don't have to type B-ELIO, just click on his icon on the screen and ProController automatically inserts it for you. You can often just respond with 'roger' or 'rgr' which means you've heard what the other person has said, or 'wilco' which means you have heard and will obey. When he calls to taxi:
B-ELIO: rgr (to the push-back and start-up clearance). Ready to taxi to the active runway.
You: B-ELIO, Taxi to runway 9 (or whatever Tower has chosen) and hold short, altimeter 1009.
B-ELIO: to runway 9 and h/s, alt 1009, B-ELIO (h/s is short for hold short)
Hold short asks the plane to get close to the point given (here, the runway) without actually getting on to the point. Each runway has a line painted on the ground (the holding line) at which a plane waiting to take-off will wait until he is cleared onto the runway (tower's duty). If you put the plane on the runway, tower might be landing a plane and this plane might well land on top of it! The altimeter is given now so that you are sure that the plane has the correct altimeter setting, and is just good practice. Even with it in your ATIS, and their take-off checks, it never hurts to be safe. Your aim as ground is just to get a queue ready for takeoff so that tower has aircraft ready to takeoff when there's a gap in arrivals.
If the pilot needs to cross a runway, he'll stop before the runway and ask for clearance. You just direct him to ask the tower for this information. Imagine for a second that there's another plane taxiing to the runway as well... tell the plane to give way:
You: B-ELIO, Taxi to runway 9 and hold short. Give way to the American Airlines 747 taxiing from left to right.
Now the pilot will have to give way to the 747 moving in front of him from his left to his right. If B-ELIO was also an American Airlines, you can use the word 'Company' to mean 'of the same company' so 'Give way to company 747...' would be legal. As a ground controller, with a detailed map, you might like to give full details of the way you want him to go, but normally the controller can just give a simple statement like the ones above:
You: B-ELIO, taxi via Inner Taxiway to block 53, then left onto taxi-way B to runway 9, and hold short.
Now the plane is ready to get onto the runway and takeoff, you hand him off to TWR, using the method you learnt in Lesson 1 by right-clicking on the plane, selecting 'aircraft >' and then 'request handoff' and select the appropriate controller. This will ask the controller for a hand-off and, when they accept, the circles around the plane will change colour, you can now go through the same menu and choose hand-off which will give B-ELIO the following message. In the real world, you'd actually say it, and in IVAO, you can just type it without using the automated system:
You: B-ELIO, contact the tower frequency 119.7 (you'd have to look up the frequency in who is on-line)
So now, it's Tower's turn to get this plane off into the sky...
If you were awaiting a plane to land, you could just leave the plane queuing, but if you are ready to have him on the runway tell him to get into position on the runway. Remember, it is your job to get aircraft onto and off the runways as quickly as possible, so that planes can land and take-off quickly:
You: B-ELIO, taxi into position and hold.
B-ELIO: Position and hold, B-ELIO.
One thing to note, Europeans may use the terminology 'line up and wait' in stead of 'position and hold' - it means exactly the same. You may also use a conditional clearance, to make your job easier:
You: B-ELIO, taxi into position and hold [after the arriving B747 / following the departing B757]
The plane may give a call back when he's ready like 'ready to go' or 'on the numbers' or 'in position'. If not, just wait until his icon stops moving and give him his takeoff clearance:
You: B-ELIO, winds calm/110@15, runway 9, cleared to takeoff
B-ELIO: Cleared to takeoff.
The plane will commence his take-off roll, and - as soon as he is airborne - you want to get rid of him and get onto your next plane. You initiate the hand-off to approach, and handoff as soon as (s)he accepts. So now, onto approaches dealings...
(In this section the approach controller is presumed to be handling departures, as there are very, very rarely departure controllers. If there were a departure controller, (s)he would deal with a departing plane, and the approach controller would deal with any planes arriving)
So approach now has a plane that wants to get on with its flight. The first thing to notice was the clearance: climb and maintain 6,000...
It wasn't explained last page, but the reason for this low height is to ensure that planes arriving at the airport - also at low heights - that are arriving from the takeoff end of the airfield are kept above the departing planes. If arriving planes are only cleared down to 8,000 ft. then - even if they have to fly over the airport and turn around - they cannot conflict with departing planes. For this reason, departing planes are usually cleared to 6,000 and arriving planes to 8,000 until they are on the 'safe' (non-departure) side of the runway.
Let's look at how the hand-off occurs this time:
EGLL_TWR: B-ELIO, contact EGLL_APP on 119.72, good-day.
B-ELIO (to you): Heathrow Approach, good-day, this is B-ELIO out of 1,700 for 6,000 on runway heading
This time, because the plane is in the air, you want to acknowledge you can see him on the radar: You: B-ELIO, Radar Contact, continue to 6,000... (and right to 120)
The aim now is to get the plane heading in the right direction (that is, towards the first VOR or NDB - remember how they're shown on the display - listed in the Flight Strip, or just in the general direction of the country he's heading to. When the planes far enough away from the airport, or there's no other traffic, climb him up to 12,000 - 18,000ft and hand him off to center. Now, a few words about giving the plane vectors (headings), remember:
- Don't expect the plane to respond instantly... think ahead. By the time he's got your message and started to turn he might be 1 NM further on that you expected.
- If he's heading directly to a 'fix' (any VOR, NDB or Intersection) give them a 'direct <place>' order like 'B-ELIO, turn left direct BIG' - don't bother trying to figure out headings when you've been given an easy way.
- Consider your heading -- are you sure you mean 90 and not 270? If the aircraft is heading to the left of the screen, he's flying a heading of 270 and not 90!! This may seem obvious, but is one of the biggest problems for new controllers.
Now the plane's in the sky, a big, bold few words about separation: Keep your planes at least 3NM from each other, or at least 1,000 ft vertically between them. If you think the planes will eventually come too close, don't wait -- turn or descend one immediately! In order to make collisions between planes traveling in opposite directions less likely, use this rule:
|Plane flying headings 0-179||Fly at ODD FLIGHT LEVELS|
|Plane flying headings 180 - 359||Fly at EVEN FLIGHT LEVELS|
What are Flight Levels? Flight Levels are used to shorten heights -- you should recognize them from the plane's blip -- you simply remove the two last digits from the height, for example 32,000ft --> FL320. Also, when you talk about Flight Levels, the pilot uses a standard altimeter setting (instead of the local altimeter setting found after the Q in the METAR weather report in the bottom right of your screen); while at low altitudes the plane will use the local barometric pressure. This means that all planes cruising will think 32,000 ft is at the same place, and not vary slightly depending on the local pressure.
Your aim is to get the planes in the right direction at a height ready for hand-off to an ARTCC (_CTR) and away from the airport. Once you've done it pass your plane onto the centre controller. It is a good idea to use the .chat <callsign of controller> function to ensure that you and your center agree on what places and heights you'll hand off at.
Now the planes with Centre. The same hand-off procedure as above applies... wait for the first contact. When you've got it, identify the plane, and report 'radar contact'. If a plane is in your airspace and won't contact you try asking on your frequency, then try a quick switch to 121.50 to send a 'Contact EGTT_CTR on 132.600' to get the plane's attention. Using 121.50 (the Guard Frequency) is used when you can't contact a plane -- all planes within a few hundred miles will hear your broadcast, irrespective of who it was intended for! Remember to switch back to your frequency -- you don't want everyone to hear your broadcasts for the rest of eternity (or perhaps you do; I certainly don't).
Centers job is pretty easy until its busy. Read the planes intended route and just get the plane to fly it. If there are other planes, make sure they don't collide. Since opposite traveling planes will have a 1,000 ft separation (using the table above) you shouldn't need to worry that much. Other than that, listen to the pilot's requests and help him where you can. When you get to your ARTCC boundary hand-off to the next centre, or - if there isn't one - give the order:
You: B-ELIO, no control available in France, resume own navigation to Belgium, radar service terminated
This statement removes all your requirements to control the plane, as it now knows that your not watching on radar, and you're not going to help him navigate. When you are navigating as centre - if the flight plan doesn't include a route - find the start and end points, and plan a quick route (either direct - give one heading - or by 'hopping' from VOR to VOR).
These terms are used often while controlling to confirm or deny requests and answer any questions:
|Affirmative (sometimes affirm or aff)||Yes or correct|
|Negative (sometimes neg)||No or incorrect|
|Confirm...||Is it correct that...|
|Unable...||Sorry, I cannot accept your request for...|
|Roger (almost always rgr)||I've heard and understood your last transmission|
|Wilco||I will comply with your orders (implies Roger)|
|Standby (sometimes stby)||Please wait, I will call you back when I am free.|
Some examples of these:
- You: Confirm current altitude is FL310.
- B-ELIO: Negative, FL290
- B-ELIO: Request descent to FL290
- You: Unable FL290 (there is already traffic at FL290?)
When the plane is nearing its final destination, make sure it has descended to between 18,000 and 22,000 ft. This means that the approach controller can take the plane and descend it quickly -- it's no good trying to descend a plane 35,000 ft in 20 NM and still get it to land. Notice that the plane should remain above 18,000 ft (in your airspace) until you've handed off. Approach might decide not to take the plane and have you make it fly circles in the sky for 20 minutes until he has some room; otherwise arrivals and departures might crash while they're being handed over! So:
You: B-ELIO, d/m (descend and maintain) 18,000 on QNH 1221, right to 270 and expect hand-off to approach in five minutes.
B-ELIO: down to 18,000 on 1221, will expect approach in five, B-ELIO.
What is the QNH? This is an altimeter setting. As the plane will shortly be moving back to local pressure, and not the flight level standard pressure, the pilot must know the local pressure. This ensures that his diagrams which give him the height of the airfield above sea level are correct -- if everyone used a standard altimeter setting at low altitudes the airport's height would seem to fluctuate over a period of hours by a few hundred feet! And finally:
You: B-ELIO, contact EGLL_APP on 192.72
I'm not sure how we ended up at Heathrow, but that's another story!
Our plane, B-ELIO, is now about 40NM east-south-east of Heathrow ready to start the approach to runway 9L - as tower has chosen runway 9R for departures, with the winds of 87@22 - the plane is at 18,000 ft and is heading at 270 (towards the left of our screen...).
Did you remember that the landing direction would be towards the right of the screen? I hope so... Anyway, planes need to be at 2,500 ft about 8NM away from the airport heading in the correct direction to intercept the magical ILS device that will guide them perfectly onto the runway. We know we need to keep the plane at 8,000 ft until its past OCK, and then get it down to 2,500 and onto the grey dotted line leading to the left runway (9L) for the ILS and tower to take the passengers safely to the ground. Formulate a plan: accept the hand-off, descend the plane to 8,000 and send it directly towards OCK VOR, at OCK descend it to 2,500 and fly it past OCK on 270, then turn it to 360 (north, easier to read than '0') up the grey dotted line pointing north, then turn it to 45 so that is cuts the grey-dotted line at 90 to runway 9L... when the plane is on a course taking it through extended center-line (an imaginary line representing a line extending from the runway) it is said to be intercepting the localizer. The plane can then be told to get itself onto this extended center-line as the ILS will warn the plane when it needs to turn to establish itself on the line.
Since the airplane is on the wrong side of the airport, we fly three sides of a rectangle, the first is known as the down-wind (since you land heading up-wind), then the next 'leg' is known as the base, and the red-line shows the final. If the plane was coming from the west, he could just fly a 'straight-in' approach, also known as an extended final - as the plane only flies a very long final.
The orange line shows the 'intercepting the localizer' as the plane will continue to fly this heading until the ILS tells it to turn right onto the center-line of the runway. As soon as the plane reports it's established on the localizer (it has direction signals), it can be cleared for the approach and told to descend with the glideslope which gives the plane height signals. The glideslope and localizer give precision approach information and are known - together - as the ILS (Instrument Landing System). Then get the plane to the tower, because - remember - you may well be dealing with planes taking off which you need to get out of your air-space, and other planes trying to get established on the ILS, as the tower wants a steady stream of well-separated planes on the ILS. You hopefully now know what you're supposed to be doing, but how do we do it. We'll look at each stage in turn.
B-ELIO: B-ELIO with you at 18,000 for Heathrow. Information Alpha. (Your ATIS - might contain weather, voice IP?)
You: B-ELIO, Radar Contact, alpha is current. d/m 8,000 and direct OCK please.
B-ELIO: rgr, down to 8,000 to OCK.
Great... B-ELIO will now get to OCK and be at 8,000. Just before he gets to OCK, you need to issue the next instructions so that he can be ready for them:
You: B-ELIO, d/m 2,500 continue present heading and expect ILS approach to runway 9L at Heathrow.
B-ELIO: rgr, 2,500 on my heading for 9L, B-ELIO.
OK so far? Now let's head him towards the airport. This is the base leg:
You: B-ELIO, turn right heading 360 (for base) the for base is for information and is usually left out.
B-ELIO: t/r (turn right) 360, B-ELIO
This is where judgment and cunning use of the feature for monitoring heading and distance come into play. It is also your duty to give the plane the frequency for the ILS (in the form xxx.xx) which can be found at www.ivao.aero/db/ss (or from database, sector system) using the search facility. The plane just hit the extended center-line at least 8NM away from the airport, so make sure you issue the turn to 45 at the correct time, otherwise B-ELIO will miss the ILS. Right place, so...
You: Turn right heading 45 to intercept the localizer on 119.21 to 9L and report established.
B-ELIO: right to 45 for LLZ to 9L, will report established
B-ELIO will now get himself onto the localizer and call:
This is your cue to clear him for the approach and allow him to descend (otherwise he'll fly perfectly over the runway at 2,500ft). This is done with the following command:
You: B-ELIO, rgr (I heard the 'established') cleared the ILS approach to 9L, descend with the g/s.
B-ELIO: Cleared ILS approach.
You: B-ELIO, contact the tower on 118.52 (if there is a tower, else you'll have to do the job... and look up the tower frequency in who's on-line)
B-ELIO: Over to the tower, thanks for your help.
That's your job done! As the approach controller you have the most work, so don't be afraid to give planes holds. A hold is a request for a plane to circle around a given fix (e.g.: a VOR) at a given height until you can do something with them. In fact, if you have lots of planes all circling a VOR, it's known as a 'stack' because the plane's are stacked there. So, we could get three planes holding at the OCK VOR (while we waited for traffic to decrease) at 6,000 ft, 8,000 ft and 10,000 ft and add new planes to the top and take planes ready for the approach from the bottom. To give a hold, the basic command is:
Hold at <vor name> VOR at <current altitude/10,000 etc. / FL120 etc.>, expect further clearance in
Which requests the pilot flies around the <vor name> VOR at the assigned altitude until you give him a new clearance. The expect further clearance (e.g.: expect further clearance in 10 minutes) just gives the pilot some idea of the delay and does not give the pilot the right to start flying away after that time is over! The full clearance for holding is as follows, but usually you can just use the one above unless you specifically need to avoid a plane coming to a certain side of the VOR:
Hold <north/east/south/west> of the <vor name> VOR on the <approach heading> radial, expect further clearance in
The approach heading is the heading at which you want the plane to approach the VOR. So, hold north of the OCK VOR on the 270 radial would ask the pilot to fly to OCK on a hdg of 270 and then to hold so he's always north of the fix. A hold is a racing track shaped rectangle.
The key to remember as the approach controller is to, wherever the planes coming from, remember its height is just as important as its direction when it comes to landing - 2,500 ft (above ground level) for the ILS.
Disaster! You've got a propeller aircraft doing an approach and you've started a 747 on the same approach behind it. There's nothing to hold it at, and there getting very close -- what do you do? You could take the plane away and start the approach again, but using an orbit -- a circle to the left or right and then on the original heading -- will increase your time, just give:
You: B-ELIO, one orbit to the left please for spacing.
Also, sometimes as approach you will want to slow a plane down to ensure that it isn't conflicting with a plane already on approach in front... if they are too close, the second plane will end up missing his approach because the plane in front will still be on the runway.
You: B-ELIO, slow to 210kts
You: B-ELIO, slow to minimum feasible speed please
You: B-ELIO, maintain minimum 190kts etc.
Anyway, back to our imaginary flight in which B-ELIO is flying the approach and is back with the tower...
Tower now has B-ELIO who is now cleared for the ILS approach, so can descend to the decision height. The decision minimum height is the height above the airport to which the plane can descend before being cleared to land. The plane cannot pass the decision height until he has visual contact (that is, he can see) the runway he wants to land on. If he cannot see the runway he will execute a missed approach and go around for another approach.
The pilot will report to the tower:
B-ELIO: B-ELIO with you to land 9L.
You: B-ELIO, Rgr. (you do not need to give radar contact, as the pilot no longer needs a radar service. He is using ILS)
You can then give the landing clearance, or - more likely - you can delay the clearance until he is 8NM from the airport and so are more certain that he will be able to land. The 8NM point of the approach is marked by a special device that causes a tone and light in the plane's cockpit. This device is known as the outer marker (O/M or OM). You can ask the pilot to tell you at this point for his clearance:
You: B-ELIO, report the O/M for landing clearance
B-ELIO: at O/M
You: B-ELIO, winds 109@17, runway 9L, cleared to land.
B-ELIO: 9L, cleared to land, B-ELIO.
Your aim as the tower is to clear the plane to land to avoid it having to miss its approach, and get other planes taking off between the landing planes, whilst maintaining separation between the planes. You must remember to account for the fact that a plane trying to land may miss its approach, and have to fly past the airport -- so make sure you turn slower planes away from the airport quickly in case a jet needs to continue past the runway.
After B-ELIO has landed, while he's still on the runway, you still control him. You want him off your runway as soon as possible, so you can land the next plane (otherwise, if he's still anywhere on the runway, you'd have to give a landing plane a missed approach), so:
You: B-ELIO take first taxi-way to <left/right> then contact ground on 121.65 (look up frequency in who's on-line)
B-ELIO: Thanks for your help, switching to ground.
And your job is done... let's look at a worse scenario. You landed a plane before B-ELIO and for some reason it hasn't been able to get off the runway yet. You must not let B-ELIO land whilst any other plane is on the runway, so you order B-ELIO to miss his approach:
You: B-ELIO initiate missed approach immediately, c/m 6000 on runway heading, and contact approach on 192.72 (again, use who's on-line)
B-ELIO: Missed approach, and will contact approach.
Approach will then climb the plane back to 6,000 ft (as it is almost a departure now) and complete the down-wind and base legs again (possibly on the other side of the airfield, depending on traffic). The plane can then be vectored back onto approach by the approach controller, and then given back to tower to try again. Of course a plane can initiate their own missed approach.
B-ELIO: No visual on runway, going around (same as missed approach), B-ELIO.
You: Rgr, c/m 6000 left to 60 (perhaps there's traffic straight ahead?) and contact approach on 192.72.
Once, B-ELIO is back with the ground controller, having taxied just off the runway, he will be given instructions to taxi to the terminal building. If there is no ground, the tower controller can just give a 'taxi to parking' order without specialized instructions.
That concludes the average flight in ProController, but the next (and last) page of this lesson contains some information that you may want to know, for example: the words used to represent single letter (e.g.: alpha for A in ATIS, and lima for L as in 'taxi-way lima' as opposed to 'taxi-way L').