|Air traffic control|
|Work in progress|
This article or section will be worked on in the upcoming hours or days.
Note: Complete rewrite in progress by elgaton
See for the latest developments.
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.
This article, written for controllers and pilots alike, will teach you that procedure and will hopefully help you to enjoy controlled areas and airports on the FlightGear multiplayer servers.
How do I know if an airport is controlled?
Check the Pilot List in FlightGear or the Multiplayer map. Usually, controllers:
- have a callsign XXXX_DE, XXXX_GN, XXXX_TW or XXXX_AP (where XXXX is the ICAO code of the airport they are manning); each callsign has a specific meaning (see "Controller roles" below);
- use the OpenRadar, ATC-TOWER, ATC (or similarly named) aircraft.
The roles a controller can assume mirror the ones that a pilot can encounter in "real life" aviation:
|xxxx_DL||Clearance Delivery||Checks flight plans submitted by pilots (or creates them) to make sure no aircraft intersects the route of another one at the same time and that visibility conditions and cruise altitude are adequate. Revokes or amends the flight plans as necessary. Assigns squawk (transponder) codes. Gives aircraft clearances (authorizations to fly to a destination airport via a certain route).|
|xxxx_GN||Ground||Controls the movement of aircraft on the ground at an airport (stands, apron, taxiways). Issues taxi clearances, assisting pilots if needed. Controls the inactive runways, but does not control the active ones; thus, a pilot generally needs to contact Tower to enter or cross them (at some fields, Ground coordinates with Tower and is able to issue runway crossing clearances).|
|xxxx_TW||Tower||Controls the runways and the airspace up to 10 NM (nautical miles) from the airport; chooses the runways to use; clears planes for takeoff and landing, making sure that they are at least 10 NM or three minutes apart.|
|xxxx_AP||Approach||Controls the airspace up to 30 NM 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/have the runway in sight (then gives the plane to TWR) or are leaving their airspace to continue their flight (then hands them off to CTR). Ensures that aircraft is adequately separated.|
|xxxx_DE||Departure||This position is rarely used, except at busy airports; it handles all the departures and hands them off to CTR, leaving the approach controller free to handle only arrivals. Coordinates closely with the approach controller to prevent collisions.|
|xxxx_CT||Center||Center (sector) controllers own all airspace not controlled by APP/DEP or TWR. They control the plane while en route, and get it from X to Y safely, until it can be instructed to descend and given to the approach controller.|
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 Airport Codes list. For example, London Gatwick is "EGKK" so a Gatwick Tower Controller would log-in as EGKK_TW.
At large airports, multiple controllers may man the same positions.
Center controllers also have ICAO identifiers, but they are not for one airport, but for a larger area. For example, LFFF_CT is France Center, and LFFF_FS is the France Flight Service Station.
Controller roles in FlightGear
Since there are not many ATCs in FlightGear, often a single controller fills more than one position. Generally speaking:
- a controller filling a particular position also fills the positions below him/her (the one listed before in the table above) if no one else is covering it; for example, if EGKK_TW (a Gatwick Tower Controller) is online, but there is no EGKK_GN, the Tower controller acts also as Ground controller;
- as an exception to the rule above, Tower controllers often act also as Approach controllers for the respective airports.
If more than one controller is manning an area, the first controller should tell the pilot to contact the second controller when the airplane is about to enter the airspace of the latter. This is usually done with the phrase: "callsign, contact station on frequency".
IFR vs VFR flights
See Flight rules for the main article about this subject.
A distinction you should know for flying in controlled areas is the one between IFR and VFR flights, as flight planning and some phraseology are different.
- VFR (Visual Flight Rules) can apply when a pilot is able to orientate and recognize other aircraft and obstacles visually (that means he must maintain a low altitude, where at most just a few clouds are present, the light must be sufficient, and there must be little or no fog at all); they are used mainly in general aviation;
- IFR (Instrument Flight Rules) apply in all the other cases.
Getting and reading charts
See Getting aeronautical charts for the main article about this subject.
You should get aeronautical charts for the airports you intend to fly from/to, specifically:
|Airport information||Describes the characteristics of the airport and provides a list of radio frequencies.|
|Ground (aerodrome chart/airport diagram)||Depicts the taxiways and runways of a specific airport; used while taxiing from and to the terminal.|
|SID/STAR||Used for instrument departures and arrivals.|
|VFR||Those charts are used for VFR flights and usually depict minimum safe altitudes for each area, as well as reporting points (you must report your position to ATC when flying over them).|
A sample IFR flight
We will teach the phraseology through an IFR sample flight from LEBL (Barcelona) to EDDF (Frankfurt am Main). For simplicity, we assume that all controller positions (delivery, ground, tower, approach/departure and center) are manned; also, we assume our callsign is BAW1542 (to be read as Speedbird one five four two).
Planning the flight
See Flight planning for the main article about this subject.
It's a good practice to file a flight plan on Lenny's website so that the controllers will be able to know your departure/destination airports, cruising altitude and route without asking you about that every time.
Follow the instructions on the Flight planning article to file a flightplan from LEBL to EDDF with a cruising altitude of FL250.
Getting the departure clearance
We start on the airport apron at terminal T1, stand 220.
The first thing we need to do is to check the current air pressure and which runway is being used; as a general rule, planes should be heading into the wind for takeoff and landing. To accomplish this, we need to listen to the ATIS (Automatic Terminal Information Service), a prerecorded message describing weather information, the runways in use and other important information for pilots and transmitted continuously on a dedicated radio channel. The frequency to use is written in the Airport information chart and can also be found by clicking on AI -> ATC Services in Range -> LEBL: in our case, it's 121.970 MHz.
We open the Radio panel, set the COM1 frequency to 121.97 and listen to the ATIS message:
- LEBL ATIS: This is El Prat information Alpha. Landing runway two five right. Departure runway two five left. Transition level five zero. Wind two zero zero degrees, one zero knots. Visibility one zero km or more, few two thousand five hundred feet. Temperature two two, dewpoint one zero. QNH one zero one eight. No significant change. On initial contact advise controller you have information Alpha.
This tells us that:
- We're going to depart from runway 25L.
- We need to set the altimeter to 1018 hPa and set it back to standard pressure (STD) at the transition level (FL050, or 5000 feet).
- Every ATIS broadcast is identified by a progressive letter of the NATO phonetic alphabet; we'll need to tell the delivery controller that we have information "Alpha" so that (s)he can checkwhether we have the latest information or not.
Note also that numbers are spelled out for clarity - this will be done in all further communication.
We now get the clearance (authorization to fly to a destination airport) from the delivery controller. The process is as follows.
- We get the Delivery frequency from the Airport information chart or the ATC Services in Range window (in this case, the frequency is 121.800 MHz) and tune COM1 to it (or connect on Mumble and joining the delivery channel).
- We contact the controller and ask for the clearance. (It is the pilot who needs to initiate contact with ATC, not the opposite). Tip: note down the clearance on a piece of paper as it's difficult (and risky) to memorize it.
- The Delivery controller gives us the clearance including:
- our callsign;
- whether we've got the latest ("current") ATIS information or not;
- our destination airport;
- the departure SID/waypoints;
- the route we'll need to follow (if it is not mentioned, we'll follow the route we wrote in our flight plan);
- the initial and cruising altitude;
- the squawk (transponder) code we'll need to set.
- We read back (repeat) the clearance to confirm we understood it correctly.
- The controller corrects any mistakes we've made and then hands us off to the Ground controller.
- BAW1542: El Prat Delivery, this is Speedbird one five four, requesting delivery to Frankfurt, flight level two five zero, we have information Alpha.
- El Prat Delivery: Speedbird one five four two, Alpha is current, cleared to Frankfurt via OKABI three Whiskey, initial altitude five hundred feet, expect flight level two five zero after ten minutes, squawk four zero zero zero.
- BAW1542: Cleared to Frankfurt via OKABI three Whiskey, initial altitude five hundred feet, expect flight level two five zero after ten minutes, squawk four zero zero zero, Speedbird one five four two.
- El Prat Delivery: Speedbird one five four two, readback correct, contact El Prat Ground on one two one decimal six five zero.
- BAW1542: Contact El Prat Ground on one two one decimal six five zero, Speedbird one five four two.
The controller asked us to follow the OKABI3W SID after departure - get the SID charts, find it and look at the chart or read the text route descriptions. In this case, the SID prescribes pilots to climb to 500 ft, turn left to intercept radial 199 PRA and be at least at 2500 ft at 8 NM from PRA; intercept radial 287 VNV and pass VNV at 5000 ft; turn right to KARDO, pass KARDO at FL120 and proceed direct OKABI. If you've got the Level-D files from Navigraph, select the SID in the Route Manager dialog for the route to be automatically entered; otherwise, use the Route Manager to input the VORs and waypoints manually.
We also set the transponder code and switch the transponder to Ground mode (if the aircraft we're using supports this functionality).
Pushing back and starting up
Before pushing back (being pushed away from the stand with a tug) and starting up, we need to get appropriate clearances from the Ground controller. This ensures we won't block taxiways unnecessarily.
- BAW1542: El Prat Ground, Speedbird one five four two at stand two two zero, request pushback.
- El Prat Ground: Speedbird one five four two, El Prat Ground, pushback approved, facing east.
- BAW1542: Pushback approved, facing east, Speedbird one five four two.
We then push back, making sure the aircraft is turned towards ("facing") east at the end of the maneuver, and ask for permission to start our engines.
- BAW1542: Speedbird one five four two, request startup.
- El Prat Ground: Speedbird one five four two, startup approved.
- BAW1542: Startup approved, Speedbird one five four two.
After that, we start our engines and complete our checklists as quickly as possible.
Taxiing to the runway
We ask for clearance to taxi to the departure runway.
- BAW1542: Speedbird one five four two is ready to taxi.
- El Prat Ground: Speedbird one five four two, taxi to holding point Echo two via Lima and Echo, QNH one zero one eight.
- BAW1542: Taxi to holding point Echo two via Lima and Echo, QNH one zero one eight, Speedbird one five four two.
Open the ground chart and check your taxi route before starting, as in some cases taxi signs will not be present at all intersections. You will notice that the controller cleared us only to holding point E2, so, once there, we'll need to report our position and await further instructions. The holding point is marked by a "stop bar" (a dotted/continuous yellow line: the dotted one faces the runway while the continuous line faces the taxiway, to remind you that you need a clearance to cross the runway, and it is lit at night by means of pulsing yellow lights).
Taxi to E2 as instructed at a maximum speed of 30 knots and hold short (stop) just before the stop bar. Remember that, while the controller may instruct you to hold position (stop) and give way to another plane, it's still your responsibility not to collide with buildings, vehicles or other aircraft; also, should you at any point become unsure of your position, stop at once and ask the ground controller.
We contact the ground controller to tell him/her we're at E2.
- BAW1542: Speedbird one five four two, we're holding short Echo two.
- El Prat Ground: Speedbird one five four two, cleared to cross runway zero two, taxi to holding point Golf one via Echo one and Kilo.
- BAW1542: Taxi to holding point Golf one via Echo one and Kilo, Speedbird one five four two.
We then cross the runway without delay and turn left on K. Near K2 you can notice a CAT II/III holding point (marked by an empty yellow rectangle with vertical lines, equipped with fixed lights) - that's where we would stop if visibility was reduced or if another aircraft was landing using ILS; since that's not the case and we were cleared to G1, just proceed.
We stop at G1 while the ground controller instructs us to contact the tower:
- El Prat Ground: Speedbird one five four two, contact Tower on one one eight decimal three two zero, goodbye!
- BAW1542: Contact Tower on one one eight decimal three two zero, Speedbird one five four two, bye!
Approaching the destination airport
Taxiing to the stand and shutting down
A sample VFR flight
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, runway 9, line up and wait.
B-ELIO: Runway 9, line up and wait, B-ELIO.
One thing to note, the phrase 'position and hold' is no longer used, since the FAA adopted the ICAO standard "line up and wait" (since September 30, 2010).
You may also use a conditional clearance, to make your job easier:
You: B-ELIO, runway 9, line up and wait [after the arriving B747 / following the departing B757]
The plane may give a call back when he's ready like 'ready for departure' or 'on the numbers'. 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 for takeoff
B-ELIO: Cleared for 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').
- In some areas (e.g. France) Center controllers are supplemented by Flight Service Stations (FSS), which provide useful information (weather, frequencies...) to pilots and do not offer air traffic control.
- European airports generally use hPa (hectopascals) for the QNH while American ones use inHg (inches of mercury). Some airplanes allow you to enter QNH values using both units; if that is not the case, you will need to use a converter.