Aviation In Canada

Friday, May 06, 2005

Descent at your Discretion, Part II

Yesterday, a response to my post about discretionary descent brought up the rate of descent a pilot should maintain when commencing descent. With a clearance to "Descend at your discretion" the AIP Canada, RAC 8.5.1 says this:

(b) If the phrase "at pilot's discretion" is used in conjunction with an altitude clearance, the change of altitude may be initiated when the pilot decides. When the change is initiated, the pilot will advise ATC. Pilots may temporarily level off at any intermediate altitude; however pilots are expected to advise ATC of any temporary level-off at any intermediate altitude. Vertical navigation is at the pilot's discretion; however adherence to assigned or published altitude crossing restrictions and speeds is mandatory unless otherwise cleared. [MEAs are not considered restrictions; however, pilots are expected to remain above MEAs].

In the paragraph immediately following the above quote, the AIP states, for information's sake, that ATC may assign your altitude to another aircraft as soon as you report leaving it. It further states that control will be based on the pilot following these procedures, and that the pilots are expected to conduct their climbs and descents commensurate with the "normal operating characteristics of the aircraft."

What's normal? Always a good question. A wide range of values would be considered normal. For example, ATC will expect a piston engined aircraft to descend and climb at a lower rate than a jet or turboprop. If you wish a cruise climb or descent, it would be good, as one reader posted, to mention that you are planning a slow climb or slow descent.

One thing that isn't mentioned, and the interpretation is arguably left open, is that once an altitude is vacated, a pilot may not return to it. That is to say, if you're descending, you must descend and not climb. This means that a "descent at your discretion" is not the same as a block altitude. If a pilot wishes to climb again, he must ask for clearance to do so, as ATC may have already cleared another aircraft to descend above you, expecting you to continue descent, or at the worst, to level off where you are.