Aviation In Canada

Wednesday, January 26, 2005

Circling Procedures, Part Two

Now that we determined in yesterday's post the requirement for an ATC clearance for a circling procedure, we should look at another important aspect. Just how far back from the airport can you start to circle for the other runway?

There are prescribed distance for this, and the distance depends on the category of the aircraft, which in turn depends on the speed of the aircraft on final. There are five categories, A through E, and the further along the alphabet, the faster the approach speed. Most jets fall into the C and D categories, while lighter aircraft typically fall into the A and B. Category E aircraft are military fighter jets, and not all approaches are drawn up to include Category E. Allowed categories for each approach will be denoted, along with weather minima for straight-ins and circling procedures, in the approach minima box at the bottom left of the approach plate. If there are no published minima for the procedure, it was not assessed, and therefore not allowed.

In any case, the area where a circling procedure can be initiated is as follows. The AIP Canada has a diagram which describes it better in RAC 9.3, as does my Weekly Topic from two years ago available by clicking here. Arcs are drawn around the runway thresholds, and lines drawn between the point of tangency of each of these arcs. The radius of the arcs is dependent upon the category of the aircraft, and is not more than 2.5 NM for a Category D aircraft, slower aircraft getting less distance. This is to allow for lower weather limits for slower aircraft, taking into account the smaller geographical area covered at lower speeds. Generally speaking, if you're cleared for an approach with a circling procedure, you still have to complete the instrument approach procedure before starting to circle. Starting the "circling manoeuver" before even making the Final Approach Fix is just not right. Doing so may very well affect separation between you and other aircraft in the air or departures launching before your arrival.