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Comment by cm2187 | Hacker News Reader

But what about the Southwest crew? The article says they waited a full minute between being cleared for take off and starting to roll. Surely they wouldn't assume the runway is the right place to hang around in a busy airport, planes typically take off straight away. If they do that it will eat into any safety margin.

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It's very likely the Southwest pilots were completing a checklist, programming their flight computer, or some other minor pre-takeoff activity before being ready to takeoff. A minute just isn't all that much of a delay. If the controller needed it to happen immediately, they should have first asked if the plane was ready, and then should have issued a takeoff clearance with 'without delay' or 'immediate' in it. Only then would be the Southwest pilots job to refuse the clearance if they couldn't comply immediately.

I am unaware if there is a formal definition of how long a controller should expect a flight to take before following a non-urgent instruction, but 60 seconds doesn't seem wild to me.

Now you could say that the Southwest pilots should have heard 'traffic 3 miles out', and understood that things need to move quickly. But as a pilot, I can say we don't have the traffic picture controllers have, particularly in bad weather. The general understanding is if we can't see other aircraft, we manage our plane, and its ATC who can get a picture of how fast the other aircraft are moving and what is safe from a separation perspective.

As a passenger that flys almost exclusively long haul from very busy airports, it is rare that my plane will come to rest on the runway, generally accelerating in the turn onto the runway and taking off.

Did they come to rest on the runway, or did they wait a minute at the side of the runway and then proceed to takeoff? I don't think you would notice the difference as a passenger, unless you were listening in on the ATC transmissions.

I can not recall a flight where I was not in a queue to depart, nor an airport where there was not a 90 degree turn onto the runway.

Without ATC I do not know when "cleared to takeoff" is given; it may be given off the runway, pilots spend a minute checking the mirrors and blindspot before turning onto the runway.

There are many runway intersections that are not 90 degree turns. They are frequently mid runway so typically only used by smaller planes for departure

Cleared to takeoff can be given before you have entered the runway, or you can be asked to “lineup and wait”.

The first means that you have permission to enter the runway, if you haven’t already, and takeoff. The latter means that you are cleared to enter the runway, but not takeoff and wait for takeoff clearance.

As a passenger there's a pretty obvious difference between "swing a turn, stand on the brakes, floor it and full send" and "swing a turn, come to a stop, sit there a minute or so, stand on the brakes, floor it and full send"

There is zero evidence that happened. They could absolutely have been sitting at the threshold to the runway for those 60 seconds and immediately took off when they turned the corner 60 seconds later

The training I got as a lowly ppl, was that a takeoff clearance meant that the runway was yours to do with as you pleased within reason. If the southwest crew needed to sit on the runway for a few moments getting setup they had permission to do it. Their job is to follow atc directions, which they absolutely did.

If the controller wanted you to do an immediate takeoff they normally make damn sure that you are able and you know the context. At least in my experience mixing it up with jet traffic at Boeing field.

Something like: “Southwest xxx cleared for immediate takeoff, you have a FedEx heavy on 3 mile final”

To the pilot that is saying: you can go, but you only have 90 seconds or so.

But surely "within reason" includes some sort of timeout?

Kind of. It’s not unheard of for the plane to have issues on the runway. Flat tire, avionics settings, whatever. That causes you a delay on the runway, or to just have to sit there and close the runway

On a regular day the controller could see this, and ask what is going on. At a small GA airport with training ops the controller is likely used to people pulling out onto the runway and taking their god damn time. The FAA actually advises wait times of as long as 2 minutes for wake turbulence, and that’s something I’ve done. Just sit there on the end of a runway.

Things get a little different, in practice, at busy commercial airports, but the rules are the same.

Used to fly out of MEM in the co-pilot seat when it was still a hub for NWA. Usually, the small planes they lined up on an alternative runway, but occasionally wind direction / strength required using one of the two (now three) parallel runways.

More than once I remember a 747, 777 or A340 taking off and getting the call "cleared for immediate departure". The pilot I was with routinely would say something like "I'm not even taxing onto the runway for 2 minutes, then we can talk".

Maybe I am thick but I am not sure I got your point. You mean he would wait 2min off the runway? Why, vortex created by larger planes?

Yeah. Turbulence from a large plane can affect small planes in really dangerous ways, and it can exist for up to 2 minutes.

So if a large plane has just used a runway, small planes will wait before taking off, whether that’s on the runway or off the side on a taxiway is up to the pilot and the tower controller.

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