I was looking through my ADSB Virtual Radar outputs couple days ago and saw a weird re-route for one of the aircraft that looked out of place.

Can one of the pilots/ATC guys pitch in to help me understand what may have caused this A/C to do this? Is this "normal"?

I would expect if this was a wake turbulence from A/C ahead they would have just asked the rerouting A/C to just slow down?

Tail #: N39463


1 Answer 1


Its hard to tell from the picture, but assuming you are talking about the yellow airplane and the "wiggle" in the course, that was probably just an S-turn for spacing. Sometimes the controllers don't get the spacing exactly right, or one airplane slows down early and messes things up. In those cases, in visual conditions, the controller can ask the following airplane to make an S-turn. This causes the plane to take a bit more time to cover the same distance as flying straight and spaces the planes out.

This may be used instead of a speed assignment for a number of reasons

  • Planes on approach may not be able to slow down further as configured
  • There may already be a speed assignment but it wasn't enough
  • Slowing down takes time, and S turn may be more efficient.

An ATC instruction may assign a heading and follow up with a new heading and approach clearance or other instructions to join final, or they may simply ask for an "S turn to the right for spacing". The vectors would be more likely in instrument conditions and the S-turn more likely in visual conditions.

  • $\begingroup$ So you know I am going to ask, why not just have the A/C slow down? Also, what might that ATC instruction sound like? $\endgroup$
    – KORD4me
    Commented Mar 10, 2014 at 2:13
  • 1
    $\begingroup$ +1. This sort of maneuver is much more efficient (and doesn't require altitude changes) than changing the speed of the aircraft would require. $\endgroup$ Commented Mar 10, 2014 at 2:14
  • $\begingroup$ @user1599043 updated. $\endgroup$
    – casey
    Commented Mar 10, 2014 at 2:20
  • 1
    $\begingroup$ @casey - learned something new, thank you! I know this is probably really basic, but neat to hear some of the explanations for things i see on my scope :) $\endgroup$
    – KORD4me
    Commented Mar 10, 2014 at 2:24
  • $\begingroup$ @user1599043 thats what we're here for! $\endgroup$
    – casey
    Commented Mar 10, 2014 at 2:27

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