SCENARIO: You’re flying a series of touch-and-go’s for practice, and the Tower controller gets on the radio: “Unable touch-and-go due to wake turbulence, Dash 8 departed thirty seconds ago, what are your intentions?”

What does this mean, and how should you reply?

A very brief wake turbulence recap

• Aircraft leave a vortex of spinning air trailing approximately behind each wingtip when they fly.
• They also leave a starting vortex (approximately one wingspan wide) horizontally across the runway as they takeoff…
• … and a stopping vortex (also one wingspan wide) across the runway when they touchdown.
• A small plane flying through these vortices can be upset, which could be dangerous.

Air Traffic Control procedures are to provide pilots with either a wake-turbulence restriction (“unable due to wake turbulence“), or advisory (“caution wake turbulence”) when you ask to take off closely behind a larger aircraft. The rules for a light aircraft depend on whether you’re following a medium or heavy aircraft:

• If a light aircraft is following a heavy aircraft, there’s a two (or three) minute restriction for takeoff. This doesn’t happen at CYTZ because no heavy aircraft use the airport.
• If a light aircraft is following a medium aircraft ATC issues a wake turbulence advisory only – unless the light aircraft starts its takeoff from further down the runway than the threshold – then they have to apply a three minute restriction. These situations occur frequently at CYTZ because the Dash 8 is considered a medium aircraft.

So why is the restriction applied when you want a touch-and-go?

Recall that clearance for a touch-and-go is clearance to land, and clearance to take off again immediately afterwards. Because the take-off roll will follow the landing it wills start some distance down the runway – it’s not considered to be a departure from the threshold. Therefore, ATC is not permitted to clear you for the takeoff implied in the touch-and-go if it will occur in this three minute period.

And that’s why when you ask for touch-and-go, ATC says “unable due to wake turbulence.” When they say “What are your intentions?” they want to know what you want to do instead.

What are your options?

You can do anything you want. Firstly you can fly a “full field circuit” – flying a whole circuit at circuit altitude – no descent, no landing, no takeoff. You just stay 1000 feet agl. That takes four or five minutes and you might hope that by that time you can do your touch-and-go. Of course there’s no assurance that another Dash 8 won’t have taken off in the mean time. Disadvantage: you don’t get to practice anything particularly useful, you just burn a hole in the sky and in your wallet for a few minutes.

Secondly you can request a “low approach”. That means you fly the circuit including the descent all the way to just before the threshold, then you pull up and go around. Benefit: you can practice a go-around. Disadvantage: you don’t get to practice a landing.

Thirdly you can request a full-stop landing. That’s because the restriction was on the takeoff part of the touch-and-go: there’s no restriction on the landing. Once you’ve landed you can ask to taxi back to the threshold for another departure. Benefit: you get to practice a landing. Disadvantage: there may be several aircraft waiting to take off and you go to the back of the queue for departure, so you may be sitting on the ground for a while.

Finally, don’t ask for a stop-and-go. A stop-and-go includes a takeoff clearance, and since you won’t be at the threshold, clearance cannot be granted during the wake-turbulence restriction time. It may irritate the controller, because then they have to come back with “unable stop-and-go due to wake turbulence, what are your intentions?“, and you’re no further forward.

Waive the restriction

Another option you have is to waive the wake turbulence restriction: “Lima Yankee Oscar waives wake turbulence restriction request touch-and-go.“. And then you’ll get your clearance: “Lima Yankee Oscar, check you’re waiving, cleared touch and go runway 26.”

Why would you do this? Well, why would you not do this? Wake turbulence restrictions are there for your benefit, and not for the benefit of Air Traffic Control. ATC doesn’t care, either way. Avoiding wake turbulence issues are always the responsibility of the Pilot-in-Command, regardless of whether or not you were given a restriction or advisory. So really you should fly the way you and you alone think is safe, at all times. It should be the existence of wake turbulence that informs your decision-making and not the issuance of an advisory or waiveable restriction by ATC.

That means that there may be times when you decide to reject an approach and go-around, possibly for wake-turbulence reasons, when ATC was silent. And there may be times when you judge it’s safe and appropriate to perform a touch-and-go (with clearance, of course) when a restriction would otherwise be in effect.

Even when you waive a wake turbulence restriction and are cleared for a touch-and-go, you still have the option of changing your mind later – you can always overshoot before touch-down, and the airspace ahead is already being protected for your takeoff. In fact, even if you’re cleared for a full-stop landing you can overshoot, and if you’re cleared for a touch-and-go you can abort the takeoff and make it a full-stop landing, just as long as you do it for a safety-related factor (not just because you forgot) and you later inform ATC of the reason.

So really what I’m saying is you don’t have to decide your intentions on the ATCO’s timetable: you can waive the wake turbulence restriction and request – and be cleared for – the touch-and-go, and make your mind up what you’re going to do later. Just do, actually, think about it. Don’t drift into a wake turbulence encounter because you make a habit of waiving the restriction and not giving it a second thought.

Things to factor into your decision

I can’t tell you whether you should carry out a touch-and-go close behind a departing Dash 8, or not. When you’re the PIC you have to make your own decisions, as always. But here are some things to think about:

• My experience is that wake turbulence behind a landing Dash-8 is much worse than behind one that departed. Depending on the aircraft I’m in I’m more likely to abort a landing because the plane ahead landed recently than because one took off.
• Strong winds – especially crosswinds – will move wake turbulence away from the runway quite quickly. If the crosswinds are proving challenging, wake turbulence is typically not an issue. Smooth air days, and calm air days, are the one where wake turbulence is more likely to be a problem.
• Dash 8’s don’t generate nearly as much wake turbulence as an Ornge helicopter practicing hovering in the airport infield¹ and you don’t get either a warning or a restriction for that.

When you’re not allowed to waive

If your light aircraft is following a heavy aircraft and is starting from further down the runway than the threshold, then you would not be permitted to waive the wake turbulence restriction, you’d have to wait out the three minutes. But most likely, if you’re following a heavy aircraft in a light one you’d rather wait, anyway. Wouldn’t you?

1. Ask me how I know :-)