Aviation In Canada

Saturday, June 25, 2005

Questions Answered

Before I continue the series, I'd like to try to answer the questions posted in response to yesterday's commencement of the Strip Writing Example. This is exactly what I'm hoping to do, is to spark some "conversation", at least as much as this format will allow.

Question one dealt with why the clearance limit was specified as the YFC VOR rather than the airport. First off, Canadian ATC actually has direction in our MANOPS which allows us to use a NAVAID rather than the airport if the destination is within our FIR. The airport should be used if it is outside the FIR. The reason? We pay attention to NOTAMs regarding facilities in our FIR, but not necessarily those outside it. For example, we'll usually know if the Gaspe VOR is unserviceable, since it's a facility adjacent to our FIR and it could affect the separation used on a route commonly flown between Moncton and Montreal FIRs. However, we don't know the status of the YYZ VOR, since it won't affect our operation. What would a pilot do in the case of a comm failure with the example clearance? Essentially the same as he would have done with the airport as the clearance limit. Comm failure rules, in Canada, allow the pilot to proceed to the clearance limit, and then to a fix from which an approach can be carried out. The time at which he is to leave the facility are specified in the AIP Canada under com failure rules, and include the latest of a number of items, including ETE in the flight plan, last estimate notified to ATC and acknowledged, etc. If I had my AIP, I could tell you properly, but it has temporarily gone missing. In any case, if ATC suspects a comm failure (sees a 7600 squawk, can't raise the pilot on radio, etc), rest assured that we'll be watching for you to figure out what you're doing.

Next, the runway assignment by an IFR ATC unit at an uncontrolled airport is a bit complicated. The pilot has to know the airspace around the airport. For example, at CYSJ, controlled airspace extends to the surface since it's in a Class E control zone. At CYCH, controlled airspace doesn't begin until 2,200 above ground. The difference is subtle. ATC can't issue taxi instructions, nor can they issue a take-off clearance, or for that matter, prevent an IFR aircraft from taking off. ATC can, however, in the case of CYSJ issue IFR clearances and restrictions that dictate when the IFR clearance is valid (and therefore when an IFR aircraft may legally take-off), and what directions he must comply with in the process. That means I can tell an IFR aircraft to depart a particular runway, but the pilot remains responsible to determine if he can depart the runway specified in the clearance, and at the time frame specified. If he is unable to do so (because of rules, traffic, weather, etc), he can certainly refuse the issued clearance and ask for something else. Since we may assign such conditions, we can narrow down what airspace we protect for the departure by assigning conditions as discussed. If such conditions are not specified, we must block more airspace to cover unexpected manoeuvers, such as a change of runway for departure if it is not specified in the clearance. In the case of CYCH, an uncontrolled airport below the base of controlled airspace, we don't have the authority to dictate such conditions, though we can specify times as to when the IFR clearance is valid.

The third question brought forward is a little more complex. As mentioned earlier, at airports that are below controlled airspace, we cannot specify departure instructions such as runway or turn after take-off. As for the obstacle clearance, the pilot is ultimately responsible for manoeuvers until reaching a published IFR altitude for the area regardless of whether the airport is in controlled or uncontrolled airspace. What is known is that for each aerodrome with a published instrument procedure, there is an aerodrome diagram which contains departure minima (visibility) and, where required, any departure procedures such as "climb gradient of 300 feet per NM is required to 1,900 before commencing turns" or any other such information. Basically, if the runway is assessed for obstacles on departure, a pilot can count on meeting obstruction clearance if he follows a few basic rules:

1. Cross the departure threshold at least 35 feet above the threshold elevation,
2. Climbs to at least 400 feet AGL before commencement of any turns, and
3. Maintain a climb gradient of at least 200 feet per nautical mile from there up to the published minimum IFR altitude (a sector altitude from an approach plate, an MEA for an airway if within the airway confines, etc).

This would be a standard departure procedure (not to be confused with a SID, or Standard Instrument Departure). In any case where the above conditions cannot meet obstacle clearance, the departure procedure will have notes and special instructions accompanying the airport diagram that detail any extra requirements either for the airport or for specific runways.

For more information on the last question, I wrote a much more detailed page on this very subject in a miniseries devoted to IFR flight and charts in my past "weekly topics" endeavor. Follow this link to find some examples and interpretations of IFR charts for departures. And remember, everything I have said here applies to Canadian airspace. Each country has their own way of assessing airports and publishing documents, so each country's regulations should be verified in their respective documents.

IFR Flight Part 2a: Departure Procedures