Aviation In Canada

Friday, January 07, 2005

Uncontrolled Airports vs Uncontrolled Airspace

A comment from my last post was related to most uncontrolled airports in Canada being in uncontrolled airspace. This is true, but has little to do with the fact that the airports are uncontrolled. The reasons different classes of airspace are established are related to traffic flow and desired levels of service within them.

In the case of many uncontrolled airports (like those with three-letter-one-number designators), many just don't have the level of IFR traffic to warrant any extra precautions. With this level of traffic, most aerodromes have an ATF, or Aerodrome Traffic Frequency, established. These are treated just like Mandatory Frequencies (MF), but aircraft without radios are allowed in them. If IFR traffic were to frequent the airports to the point where IFR-VFR conflicts became an issue, the airspace in the area may end up being reclassified as Class E controlled airspace to raise the weather limits for VFR flight, thereby giving a better shot at letting the see-and-be-seen concept work. This would also mean separation would now have to be provided between IFR aircraft. Were an airport to become busier yet, a control zone may be established to once again ensure higher weather limits are necessary for VFR flight now around the airport itself, instead of just the area around it. A CZ is controlled airspace from the ground up to a defined height, which probably enters the base of surrounding controlled airspace. Note that a CZ in place doesn't necessarily mean that an airport control tower is in place. At this point, we have a CZ with controlled airspace to the ground, but it's likely Class E, which permits VFR without talking to ATC, but IFR need a clearance. A Class E control zone normally has a Mandatory Frequency assigned to it, and often has a Flight Service Station established, either on site or for RAAS (Remote Aerodrome Advisory Service by RCO). Again, another increase in traffic might warrant the establishment of a tower, and now the CZ would likely get a designation of Class D, meaning airport ATC has authority in the airspace and VFR must contact ATC to enter.

An airport with a lot of VFR-VFR could also meet requirements for a tower to be established, even without the IFR traffic. This is somewhat more rare, but it does happen. These areas are often already surrounded by controlled airspace, since it would happen in areas which are already busy with other traffic.

This is why so many of our uncontrolled airports are in uncontrolled airspace. The traffic levels just aren't there to require it. Uncontrolled airports and uncontrolled airspace are sort of disconnected. A controlled airport always means controlled airspace, but controlled airspace doesn't always mean a controlled airport.

All of the classificiation of airspace can be found in the Desingated Airspace Handbook (DAH), which is downloadable from http://aero.nrcan.gc.ca/english/ATS_dah_e.html, and the Canada Flight Supplement has information on individual airports and their facilities.