Base of Controlled Airspace
In Canada (as elsewhere, but I'll only speak for us), the base of controlled airspace depends on the area where you are. In the southern areas of Canada, the base of controlled airspace is much lower than in the far north. The Arctic Control Area, the far north of Canada's archipeligo, has Class A airspace based at FL270. The Northern Control Area is based at FL230, and the Southern Control Area, where all the most populous places are, Class A is based at FL180 (or more correctly worded, "18,000 MSL and above").
Class B is considered to be "controlled airspace above 12,500 up to, but not including, 18,000 MSL". Therefore, if it's classed as controlled airspace between these two levels, it's Class B. An example of where Class B begins above 12,500, could be an airway. Airways are controlled airspace which begins at 2,200 above ground level. A mountain topped at 14,000 feet would push up the base of controlled airspace of an overlying airway, and therefore the "floor" of Class B airspace, to 16,200 feet. Below that would be Class G.
The trick is to read the charts to see where the base of controlled airspace is. A Canadian LO chart (low level enroute) has areas shaded with solid green as uncontrolled below FL180. The cross-hatched areas (green with white lines) are drawn to denote areas where the base of controlled airspace is "above 12,500", meaning Class B. The areas without shading (white) denote other levels, which may be 5,500, 2,200, 1,700, 700, or indeed any other specified level (the three latter examples are common values expressed in elevations AGL).
The example flight I mentioned the other day about the Dash 8 meeting another piece of aluminum was around Bathurst, NB (CZBF), where the base of controlled airspace on the Canadian side of the US/Canada border is above 12,500, while the base on the other side is much lower. One reader posted about US airspace and there not being much Class G. Interestingly, another difference between Canadian and US airspace is that US IFR approaches much be contained within controlled airspace. This is not a requirement for Canadian approaches, and there are many examples of airports which underlie controlled airspace but have one or more approaches published.
Class B is considered to be "controlled airspace above 12,500 up to, but not including, 18,000 MSL". Therefore, if it's classed as controlled airspace between these two levels, it's Class B. An example of where Class B begins above 12,500, could be an airway. Airways are controlled airspace which begins at 2,200 above ground level. A mountain topped at 14,000 feet would push up the base of controlled airspace of an overlying airway, and therefore the "floor" of Class B airspace, to 16,200 feet. Below that would be Class G.
The trick is to read the charts to see where the base of controlled airspace is. A Canadian LO chart (low level enroute) has areas shaded with solid green as uncontrolled below FL180. The cross-hatched areas (green with white lines) are drawn to denote areas where the base of controlled airspace is "above 12,500", meaning Class B. The areas without shading (white) denote other levels, which may be 5,500, 2,200, 1,700, 700, or indeed any other specified level (the three latter examples are common values expressed in elevations AGL).
The example flight I mentioned the other day about the Dash 8 meeting another piece of aluminum was around Bathurst, NB (CZBF), where the base of controlled airspace on the Canadian side of the US/Canada border is above 12,500, while the base on the other side is much lower. One reader posted about US airspace and there not being much Class G. Interestingly, another difference between Canadian and US airspace is that US IFR approaches much be contained within controlled airspace. This is not a requirement for Canadian approaches, and there are many examples of airports which underlie controlled airspace but have one or more approaches published.
posted by Michael at
12:27
