In case you have ever wondered about ATC slots, Sylvia, the blogger behind the Fear of Landing blog has written an informative post to clear up any misunderstandings that you may have about the allocation of slots. Sylvia began her post by noting that there is always a tendency to blame the airport after an announced delay about a flight missing its slot or being given a bad slot. Sylvia then noted her explanation for how slots work:
- If you are flying VFR, you are flying visually and you choose the route as you go – just like a sail boat.
- On the other hand, IFR flight fly routes which they must apply for and be approved of in advance. Since an IFR flight is not using the see-and-avoid method, traffic must be managed to ensure that no airplanes are in the exact same place at once and as part of this planning, a slot time or a specific slot is allocated.
In other words, missing a slot is like missing the flight itself and the plane will just have to wait.
However, Sylvia also contacted “Jumpseater,” who blogs at Norven Munky’s Weblog, who came up with the following and by far the best and easiest explanation for how ATC slots work:
Idiot’s Guide to ATC Slots
ATC slots are issued as a function of airspace capacity.
It’s very simple: if you have a room that holds ten idiots, you can’t put eleven idiots in the room, as much as you might like to.
Idiot number eleven has to wait until one or more idiots come out or the room is made bigger, so the idiot (No11) is given a slot time. This is the time the idiot has to present himself to commence his journey to the room.
If there’s only seven idiots in the room, then you can get three further idiots in there without restricting their progress at all, but the fourth idiot and any subsequent idiots will have to wait their turn.
If that room is in fact a corridor joining two rooms, then you can only get so many idiots down that corridor at any one time, even if the room at either end has a limitless supply of idiot capacity. Therefore any idiot wishing to pass through the corridor may get a slot time for the corridor, depending on how many idiots wish to use the corridor at any given time.
If there is another different corridor joining the rooms, you can send the idiots down those corridors, which may mean that the idiots will not be restricted at all.
So using the above Idiot’s Guide, you should be able to see that ATC SLOTS do not get secured by an airlines schedule or their staffing levels, they are a tactical daily/hourly response to airspace capacity.
So the next time you are a passenger grumbling about an announced delay because your flight missed its slot or was given a bad slot, just remember both Sylvia’s and Jumpseater’s informative explanations.