Separation (not the Quebec kind)

There’s really only one thing that air traffic controllers spend a lot of time worrying about, and that’s separation. Separation means that each aircraft has an invisible bubble around it. When a controller is required to separate aircraft, she has to make sure that neither aircraft enters the other’s bubble. If she messes up once, she’s in big trouble; if she messes up a couple more times, she’s fired.

When a controller is not required to separate two aircraft from each-other, he’ll probably still point out traffic and do his best to keep you apart, but if you come too close to each other it’s usually the pilot’s responsibility, not the controller’s. As a result, if you want to get in trouble, the most effective way to do it is to do something that causes a loss of separation — the controllers will let you get away with almost any other bonehead move while you’re in the air, but it you cause a loss of separation, they will have to turn you in to Transport Canada to save their own behinds.

Of course, there are worse ways to get in trouble than with Transport Canada. Even with a fine and penalty, and you’ll probably fly again; get into a midair collision, and the outlook is a bit darker. As a result, it’s very important to know two things:

  1. Is the controller providing me with separation?
  2. If so, what is she separating me from?

To figure out the answers, it’s important to know what kind of airspace you’re in (note that this applies to Canadian airspace — US airspace has some important differences):

Class Description IFR VFR
A All airspace from FL180 (higher up north) to FL600 All aircraft (no VFR)
B Controlled airspace from 12,500 ft to FL180 All aircraft All aircraft
C Busy towered airport control zones, and major terminal areas below 12,500 ft Other IFR aircraft, and VFR only to resolve conflicts With IFR aircraft when necessary to resolve conflicts
D Less busy towered airport control zones, and less busy terminal areas below 12,500 ft Other IFR aircraft only No separation
E Airways below 12,500 ft, towered airports when the tower is closed, MF airports with an FSS, control zone extensions, etc. Other IFR aircraft only No separation
F Any special-use or restricted airspace Not usually No separation
G Totally uncontrolled airspace No separation No separation

So if you’re flying VFR on an airway at 14,500 ft, you’re in class B airspace, and ATC will be separating you from all other aircraft. On the other hand, if you’re flying IFR into Oshawa airport (class D), ATC is not responsible for separating you from any VFR aircraft in the zone, even though they probably will give you advisories, so keep a sharp lookout when you break out from the clouds.

Note that I haven’t gotten into the other kind of separation here, separation from terrain and obstacles. I think that’s normally both the pilot’s and controller’s shared responsibility, except when the plane is on vectors, but I haven’t double-checked (I always assume it’s my problem anyway).


About David Megginson

Scholar, tech guy, Canuck, open-source/data/information zealot, urban pedestrian, language geek, tea drinker, pater familias, red tory, amateur musician, private pilot.
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