Aviation In Canada

Wednesday, May 04, 2005

Surveillance Approach

Have you ever heard of a surveillance approach? Any idea what it is?

It's an emergency procedure that pretty much has to occur in a pretty nasty situation. A PAR or GCA is the classic, "talk a pilot down," approach where a radar gives a picture to ATC of where an aircraft is in relation to the final approach course and the glidepath with two separate antennas, one scanning the vertical and the other the horizontal. These antennas make rapid passes of the approach area to give a fast refresh rate for the controller, allowing him or her to react quickly to give guidance to a pilot. It's near continual talking to give a pilot the position information he needs to fly a precision approach -- one with glidepath information. They have fallen out of favor and are mostly relegated to the military now, since ILS gives the pilot the same information and it's right in front of his eyes.

The surveillance approach, on the other hand, is a similar kind of tactic but it varies in a few, but significant, ways. First, there is the conspicuous lack of glidepath information. It is done with enroute radars, and therefore the only possible attempt at vertical guidance is through recommended altitudes, typically given at each mile on final. The keeners would recognize that ATC's enroute radars turn comparatively slowly (in Canada, once every 4.8 seconds, in the US I understand that some are as slow as once every 10s, but I stand to be corrected here). This means that another significant difference is the update rate. And last, enroute and terminal ATC don't exactly get regular practice on such a procedure the way a PAR controller would. It's an emergency procedure only, but it is still in the toolbox, should it ever be needed. And it's not meant to be an IFR approach, either, so much as a cloud breaking procedure. Like a PAR, it can't be conducted just anywhere on the fly. Only airports that have reasonable radar coverage are candidates for it. This would include most of the major airports in Canada, but few of the "satellite" airports, except those lucky enough to be near a radar.

If you're instrument equipped and trained, you'd be better off with a real IFR approach. If you're not IFR equipped, you'd be better off maintaining VFR on your own, in my opinion. Also, if you're destination in one that is served by a radar and their weather is bad, don't just go asking for this as a way to get home. Find another suitable field and land to wait out the weather there. An unnecessary surveillance approach will require a declaration of an emergency, and will get you a lot of unwanted attention if your situation wasn't really that bad. Still, it's good to be aware that such a thing exists, should it be one of the few options available.