Common Questions about ATC
Over time, certain patterns appear in bug reports, questions and occasional flat-out strops about the ATC system and how it works. While I’m making no attempt to say that it’s perfect – trust me, I know very well it’s not – a lot of the things that come up regularly are easily explained and, in most cases, down to misunderstanding or misinterpretation. This article, which I expect to grow over time, will cover the most common points.
Basic Misconceptions
ATC is not route guidance
If you’re used to hearing a GPS in a car issuing turn directions you might easily think that ATC is basically a three-dimensional version of that; it just gives headings and altitudes to move you along whatever route you have in your FMS and if you take a shortcut or change your mind, it will just recalculate and give you the next best route. This is not true. ATC is a safety service, not a route guidance service. To be flying in the first place, it’s assumed that you’re competent to follow a route yourself. ATC guidance comes in only when the route is insufficient, or you’re in a busy environment and safety concerns are more relevant than waypoints.
You can’t just disregard an ATC instruction because you think you know better, or you simply want to do something else. ATC has the overview of what’s happening in the entire region around you and requires that you follow their guidance to keep everybody safe.
Your FMS is irrelevant to ATC
The controller you’re talking to neither knows nor cares what your FMS is telling your autopilot to do. The unspoken contract is that the controller will keep you safe provided you follow their instructions. The FMS is there to assist you to follow those instructions and nothing more. If the route in the FMS doesn’t match what you filed, or what ATC is telling you needs to be done, reprogram your FMS.
Why does ATC keep telling me to “descend and maintain 10,000 feet” when I’m already there?
Incorrect altimeter setting
Possibly the most common thing reported as a bug, being told to “descend and maintain 10,000 feet” or similar while the aircraft appears level at 10,000 ft is down to your altimeter setting. If you’ve left it set to 1013 (or 2992 in the USA – different units) when you descended through the transition altitude, the altitude that your altimeter shows will be different to the one the ATC controller sees you at. If in any doubt, use the “Request Altimeter” radio call.
The same principle applies if your altimeter is set to anything except ISA above the transition altitude. Also, always check what the transition altitude and layer actually are in your location – especially for Americans, remember that the rest of the world does not have these set at a uniform 18,000ft.
Finally, always use the pressure setting given by the controller you’re talking to! No other source – for example your destination airport, pressure at the aircraft’s exact location or an online source – will give you the correct value.
Misinterpreted instruction
The other variant of this is when the actual command is misquoted. Originally it was “descend and maintain FL100”, not “descend and maintain 10,000 feet”. These are not the same thing! Any altitude given as a flight level tells you that the pressure setting must be ISA, while any altitude given as feet tells you that the pressure setting must be whatever “altimeter”, “QNH” or “QFE” the controller stated.
Obviously for both of these, the same applies for any altitude-related command, and for any altitude, not just 10,000 feet.
Why does ATC stop issuing climb or descent instructions during IFR flights?
Misunderstanding of what procedures (SID/STAR) really are
Many people believe ATC has stopped working because no further climb or descent instructions are given after departure or before arrival. If you are using a procedure – a SID, STAR or APPCH – these often contain restrictions on both speed and altitude, and even the direction in which to make a turn; they are not simple lists of waypoints. You are expected to obey all restrictions without spoken guidance, that’s the point of having published procedures, so the controller will not transmit per-turn instructions unless you stray from the published route – including the restrictions.
Not listening to the controller’s instructions
Pay attention to prior messages! You may get more than one action in the same message, including future actions, such as “Climb now to 13,000 feet then climb pilot’s discretion to FL340”. You won’t get a second instruction to climb to cruise altitude after you reach 13,000ft or when the SID ends, that clearance has just been given to you.
Why does ATC not confirm the SID or STAR I filed in my flightplan?
It seems that there is a widely-believed misconception that the “Issue Procedures as Vectors” checkbox in the flightplan dialog is just a way of having the controllers read out your turns for you instead of staying silent. This is not true. If you use that checkbox, or make the “No Procedures” radio call, or use “NO SID” or “NO STAR” as part of your filed route, you are telling the controller that you or your aircraft are incapable of following a procedure. If you do this, you should not hear any procedure name mentioned at all for the entirety of the flight.
This does mean, though, that if you don’t get assigned the procedure you expected, even if you filed one, you are not going to hear the name of the procedure you did get assigned. (The controller is free to use a published procedure for your route, they just won’t ask you to fly it autonomously). This is intentional! By stating that you are incapable of flying procedures, you have committed to following per-turn instructions which means that it will be impossible to preset your FMS with a particular route. It’s up to you to make the turns, altitude changes and speed changes exactly as the controller states, exactly when the controller states, without knowing what procedure if any they belong to.
ATC gave me crazy turns as soon as I started flying the STAR!
You’ve set your FMS incorrectly after declaring inability to fly procedures
If you’ve told the controller that you’re unable to fly procedures then any procedure you programmed into your FMS, whether for departure or arrival, is instantly and automatically wrong except by blind luck.
You’ve set your FMS incorrectly for the granted clearance
Another variant of this is simply that you weren’t assigned the STAR or other procedure that you requested in your plan. Your plan is a request, not a command, and if operational reasons mean that a procedure you requested is not currently usable you’ll be assigned an alternative. Listen to the controller’s response to your clearance request when filing the plan, and when you hear “Expect <procedure> arrival” or “Descend via <procedure>” as you approach your destination. Always use that as a trigger to check that the procedure you’ve been allocated is the one programmed into your FMS.
I ended up almost overhead the airport at 13,000 feet!
Just because you’re headed straight for a runway doesn’t mean you’re going to land on that runway. Many airports have procedures that take you directly overhead the airport at altitude and then descend on the far side while executing a procedure turn to put you back on the glideslope for the other end of the same runway.
As with “crazy turns”, always check that the runway stated in the “Expect…” and “Descend via…” or approach clearance calls matches the one you set in your FMS, and the one you try to land on.
Why does ATC tell me to climb near the airport while on approach?
Closely related to the previous question, this happens if you’ve descended below the commanded or cleared altitude. Remember, that altitude may be an unspoken restriction in the published procedure and it’s up to you to check and obey these! Especially if you’ve seen a runway dead ahead and descended sharply to land on it, check that you’ve not descended below the cleared altitude and that you’re not trying to land on the wrong end of the right runway.
Why did ATC tell me to descend to a crazy low altitude for the whole length of the STAR?
There is a difference in phrasing in different parts of the world. In some locations you will be told e.g. “Descend via <STAR> to 5,000ft”. This is saying that the final cleared altitude is 5,000ft, not that you must descend immediately to 5,000ft and then stay at that altitude for the next 70 miles. You should obey all altitude restrictions published as part of the procedure, exactly as in any other case.
What’s this “Descend via <STAR> except maintain 12,000ft until <WAYPOINT>”?
Yet another version of “procedures contain altitude and speed restrictions”, this tells you that you should maintain the stated altitude until a certain waypoint, after which you should obey the published restrictions without further instructions. This will be used in the case where you’re already below some of the higher restrictions. There’s a very similar version for climbing out on a SID where your final cruise altitude is below some of the higher restrictions.
Why did ATC tell me to climb on a SID and then immediately descend to 4,000 feet afterwards?
Check your flightplan both before and after filing it! If you’ve used a very low cruise altitude, often done by people typing e.g. “360” intending “flight level 360” but actually meaning “360 feet”, ATC will round up to the minimum safe altitude for the route. You will be told this when the controller reads you your clearance, and you will read it back to the controller. This situation comes about when you have a mistakenly low cruise altitude and a SID with no conflicting altitude restrictions.
If there are any differences between what you requested in your plan and what’s actually issued, they will be listed in the controller’s spoken clearance with the word “except”. If you do make this mistake, remember that you can request cruise altitude changes. It might take a few steps because the options available here are restricted to keep menu sizes reasonable.
Why does ATC think I’m off course when I’m not?
The route in your FMS doesn’t match the route you were cleared for
A common cause of this is that the route you filed is not the route you programmed into your FMS. You may have missed a waypoint either in the plan or in the FMS, or you may have altered the route in your FMS after filing the plan.
The rule is that if you file it, you fly it. That said, you can often recover from this situation if you request “Direct to navaid”, where each navaid on your filed route will be given as a choice or, of course, entering the missing waypoint into your FMS.
Also see above, the “crazy vectors on arrival” questions.
Your autopilot isn’t turning fast enough
If you’re getting vectors for departure or approach, and you’re flying on autopilot, check the turn rate limiter if your aircraft has one. Slow, gradual turns at low rates are fine for cruise but during this stage of the flight when you’re told to turn you need to turn immediately, and potentially sharply. Remember, STARs are published rather than invented by the sim and will frequently contain tight consecutive turns which require a high bank angle.
Why does ATC not just use my FMS? That’s the route I wanted!
How does a person sitting in a room hundreds of miles away see a six-inch screen in your cockpit at 38,000 feet? You request a particular route in your plan; ATC will monitor you along that route, and exactly that route, and give guidance where necessary; you respond to that guidance by programming your FMS to reduce your workload. The FMS is the last step in the chain of command, not the first.
Children of the Magenta Line consider this to be heresy.
Why does ATC never tell me to descend?
You’ve been mis-using the cruise altitude change
If you’re using repeated “Request Altitude Change” requests to perform a descent to your destination, you’ve missed the “Request Descent” call. The first is for changing your cruise altitude, not performing a manual step descent.
As you approach your destination you will have the option to “Request Descent”, to initiate the descent phase of the flight. If you leave this late, the controller will eventually prompt you to start descending. By continually requesting lower cruise altitudes what you’re actually doing is pushing that controller-initiated descent instruction further and further forward to the point where you can end up at a few thousand feet close to the airport without the actual descent phase starting.
Your route isn’t what you think it is
If you don’t see the “Request Descent” call as an option then re-check the route you filed – this will always be available in the ATC dialog’s transcript. In one case, someone accidentally filed a navaid nearly 1,800 miles beyond their destination as an intermediate waypoint so even directly overhead the airport, they still hadn’t had the descent instruction. Of course they hadn’t – they still had 3,600 miles to fly before they needed to descend!
Why do I fly directly overhead the airport before getting the descent instruction and get vectors taking me away from the airport again?
As in the previous question, if you file it, you fly it. Don’t file any waypoint closer than the initial fix for the STAR you wish to use. If you file the airport name itself, or a navaid on the airport, as part of your route you’ll be expected to fly to that navaid and only then enter the approach and landing phase. Especially if you’re very close to the airport, you’ll almost certainly be directed away from it to a point where you can join a procedure or a standard pattern approach.
Why did ATC give me turns taking me away from the runway?
This is not the runway you’re looking for
The most common reason for this is that you’re landing on the wrong runway. Remember to check the runway that’s specified in the “Expect…” and “Descend via…” calls – it may not be the one you intended. It may well not be the one closest to you, or the one that an online flight-monitoring website says is in use, or even the one that’s best aligned for the wind. You may be expected to land on the other end of a runway dead ahead of you – as above, just because you’re headed for it doesn’t mean that’s the runway you’re landing on.
You’re too close to the airport
The other possibility tends to come after a manual (and incorrect) step descent using repeated “Request Altitude Change” commands. If you end up too close to the airport you may well be repositioned further away before getting final approach vectors. The same will happen if you’ve ignored previous turn instructions and headed straight for the airport.
How do I know which runway to select when ATC only gives me a SID during clearance?
When you file your flightplan before departure, it’s reasonable to expect to be given the departure runway. The delay here is that some time may pass between filing the plan and executing it – pre-flight checks, loading etc. – in which time the active runway may change, or a different runway in the active set may become a better one to use. You’ll be given the actual departure runway when you request taxi. In the meantime you can find out what the actives are using ATIS.
Tumpty-tumpty-so I just ignored that and turned/descended
Wrooooooooong! If you’re being given vectors or any other explicit instruction, you need to follow that instruction. You also need to not make turns or altitude changes without explicit instructions when you’re under ATC control (except for flight following of course). It’s ATC’s responsibility to keep you and everyone around you both in the air and on the ground safe and that’s not possible in a busy, near-airport environment if every aircraft just makes it up as they see fit.
ATC will never ask you to do something that looks outside the capabilities of your aircraft, or which would be dangerous. If it does, that’s a clear bug and needs to be reported so it can be prevented. If you don’t understand why you got a particular instruction, or why you didn’t get one you were expecting, review the message transcript because 99 times out of 100 this shows a disconnect in understanding rather than an error in the controller’s decision-making.
If you go off-piste then the controller will diligently – and tirelessly – try to get you back on track. This may well involve repositioning you further away from the airport if you get too close. If you’re simply beelining for the brightest set of PAPI lights, the closest runway to your heading or a runway that’s set in your FMS even though it’s not the one you were told to land on, they’re not going to just throw up their hands and say “Oh, go on then”.
Why does the “Get from FMS” option not work?
Not all third-party aircraft, notably those with custom avionics, support any kind of interaction with the simulator’s default systems. Even though they would be able to read and write to the default avionics and transfer the routes to and from their own custom versions, this is just not done. X-Plane makes the information about routes available but can not force third-party developers to use this information.
Why didn’t the approach controller clear me for approach?
Depending on the airport’s level of control, you may need to call the airport directly rather than have a regional or approach controller clear you and hand you over. Outside the US this is common for smaller fields – typically but not exclusively GA-focussed airports. Even if you’ve filed a plan, you will be taken very close to the airport and then told to contact them directly to request landing.
I can’t make any radio calls except “Uncertain of Position” and “Radio Check”
You’ve left a controller’s frequency with outstanding readback. Obviously in real life this doesn’t prevent you from making new calls to a different controller but it’s bad practice. The sim indicates this by making you go back and complete your readback before allowing you to check in with the new controller.
Another possibility is that you departed from a FISO airfield and didn’t tell them you were leaving their frequency. This is also bad practice.
Flight Following: I didn’t get handed off properly
When you’re getting flight following, services from ATC are generally provided at their discretion. If they’re too busy, or in a part of the world where coordinated handoffs are less likely, you may not get a coordinated handoff when you fly into another controller’s airspace. In that case, it’s up to you to re-request flight following from the new controller.
Flight Following: I’m not getting turn instructions
Flight following is not the same as following a flight plan! This is a service targeted at unplanned flights, generally GA flights, where the pilot wants to be in contact with a controller for safety and coordination but is free to fly as they wish provided they obey basic rules.
This is not a way of avoiding getting strict vector instructions on landing! At a controlled airport you will still be given vectors and will still be expected to follow them precisely.
Flight Following: I didn’t get handed off after departure
As with many things in flight following, the pilot must use their own initiative at certain times. If you depart a FISO airfield they will not hand you off as you approach the edge of their airspace or ATZ. It’s up to you to tell them you’re leaving their frequency before switching to a new frequency to request flight following.
I can’t contact my destination and I’m only 80 miles away
Check that your destination actually has a person you can speak to, either fully-controlled or a FISO. If they only have UNICOM/CTAF, that’s not yet handled by X-Plane and the frequency will be empty. For smaller airports, and especially small FISO airfields, you may simply be outside their transmitter range. This also takes account of terrain so if line-of-sight from you to the airport is broken the effective transmitter range will be reduced. Finally, the airport may simply be closed (i.e. out of working hours, not temporarily closed due to unflyable conditions) and there is simply nobody there to answer your call.