So I was wondering. How do you ATC crew know when to clear one plane to takeoff after another? How long do you have to wait before you are able to clear the next plane to takeoff? Is there a certain distance you need to wait for before you can clear the next plane?
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Separation requirements are outlined in Section 3.1 of the ATC Manual.
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Although it’s relatively rare, but ATC may also slow the departure rate intentionally for various reasons. This practice is called flow control.
You may notice flow control being implemented especially at VA events (fly-outs) if most pilots are bound for the same destination. You may also see this happen if a controller opens an airport that is “feeding” the hub, which already has a congested airspace.
Flow control eases the workload of Approach controllers at the destination and can do heaps in reducing airspace congestion. We usually measure flow control either in minutes or distance (nm). For example, one departure out every 3mins or 5nm.
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So it’s normal for me to line up and wait and then be held for 3 or so minutes after the last aircraft took off? I used to think they forgot about me
Most Local (Ground+Tower) controllers are controlling 3 frequencies at the same time. And occasionally, there might be a wave of traffic,for this example - on ground frequency requesting pushback, taxi, etc instructions at the same time. During such a mini wave, it may be a priority to instruct those X number of aircraft on Ground frequency, prior you are cleared for take-off on Tower frequency just simply to avoid and ground conflicts.
Another scenario may be that there is an intersecting runway that is being used for landing. In this scenario there may be a wave of inbound traffic with minimum separation and this will require the controller to occasionally prioritise those planes landing and getting off the runway.
Of course, at the end of the day we are all humans and skill mistakes can happen. IFATC take great pride in training and maintaining a high standard of our operations, but small mishaps happen! Just remember that when you have 1 aircraft to worry about - controller can have 10-30 airplanes requesting various items at once!
I hope this helps and clear skies!
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Only if flow control is being implemented by ATC, then yes.
Otherwise, by default, controllers will follow the seperation minima shared by Aatogamer above.
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