Saturday, June 13, 2009

When Is a Tower Not a Tower?

I've been getting some questions in comments lately about airport control towers. This post is about air traffic services at Canadian airports, from a pilot's perspective. The controllers and specialists themselves might describe it differently.

First off, the ultimate authority regarding runway selection, wake turbulence separation, altitude of flight and everything else about the flight rests with me, the pilot. I am required to follow any air traffic control instructions which I accept, but if an air traffic controller clears me to do something illegal, and I do it, I still get in trouble for it. If a controller instructs me to do something dangerous and I do it, I still die. Next, any pilot is capable of navigating from any airport to any airport without the assistance of air traffic control. Any pilot, from the student pilot on his first solo, right up to crew of an Air Canada jet coming across the Pacific from Japan, knows how to safely finish a flight with no radio at all. Many flights are conducted every day in Canada in aircraft that are not radio-equipped. Air traffic services greatly increase the safety and efficiency of air travel, in much the same way that traffic lights increase the safety and efficiency of the highways.

Look up any Canadian aerodrome in the Canada Flight Supplement (CFS) and you will find at least one of the following. (You could find more than one if for example the control tower closed at night leaving either an FSS or a MF).

  • a tower
  • a flight services station (FSS)
  • a mandatory frequency (MF)
  • an aerodrome traffic frequency (ATF)
  • the aerodrome is not listed at all

If there is a tower frequency listed in the CFS, there is probably also an ATIS and ground frequency and could be more frequencies for clearance delivery, outer tower, different areas of the ground, and so on. Call any of these frequencies and you are speaking to someone sitting in a physical tower overlooking the airport. They may not have a clear view of the whole thing. They may be 1/8 SM in fog and see nothing out the window. It could be one person operating both the tower and ground frequencies. (I think in that case there would someone else in the break room getting a coffee, and that at a Nav Canada tower no one works a solo shift, but I could be wrong).

If there is a tower, as there are at about forty Canadian airports, then a pilot starting up at that airport will request permission to taxi up to the edge of the runway and then report ready and wait for clearance to enter the runway and take off.

Fort McMurray Ground, GABC on the east apron, request taxi for VFR to Grande Prairie, six thousand five hundred.

GABC, McMurray Ground. Taxi runway 25 via alfa, call tower holding short of 25.

I acknowledge that, trundle up taxiway A to the line marking the edge of the runway and finish my checks before calling...

McMurray Tower, GABC ready 25 on alfa

GABC, cleared takeoff 25

I acknowledge that, and take off, if everything looks safe to me.

I left out some other things we would probably tell each other, but the basics are there. I ask for what I want, they give me instructions and clearances.

About fifty Canadian airports have an FSS but no tower. There may actually exist a raised structure with a good view of the field, and the flight services specialist may indeed sit inside it and look out at the airplanes going by, but when we say there is or is not a tower, we are referring to a tower frequency and the requirement to obtain clearances for movement. The reason I said "about forty" and "about fifty" is that towers and FSSes open and close according to need, so a tower that was occupied by air traffic controllers last year houses an FSS this year. Some FSSes don't have towers, just regular buildings, or even portables. If I want to go somewhere at a field with an FSS but no tower (even if the FSS guys are in a tall skinny building that used to be called a tower) I call the FSS and tell the specialist what I am about to do. An FSS is addressed with the call sign "Radio."

Grande Prairie Radio, GABC on the east apron, taxiing for VFR to Fort McMurray, five thousand five hundred.

GABC, Grande Prairie Radio. Active runway is 12. Traffic is a King Air landing 12 in two minutes.

I see the King Air touch down and go past the intersection. Everything looks safe, so I call..

ABC rolling 25.

Again I left out the FSS giving me the wind and altimeter setting. The difference is that the tower tells me what to do, and I decide if it's safe, while the FSS gives me information and I make a decision based on that. The line blurs of course, because the tower may offer me a choice and the FSS may give me a recommendation, but in the end I ask the tower but I tell the FSS. If I'm departing IFR into controlled airspace, the FSS gives me my IFR clearance.

At all the other airport, some of which may have tower like structures that used to house an FSS or control tower, but are now unoccupied, or used to store paint and frangible taxiway lights, I make calls to traffic. I make calls just like the ones I made to the FSS, but now I talk to "traffic" instead of "radio". There may or may not be anyone else listening to the traffic frequency. If there is, they will tell me if i pose a conflict. If the airport has an MF, then I have to have a radio, listen on the frequency and make appropriate calls. If the published frequency is just an ATF then if I have a radio I should make the MF-style calls, but aircraft using that aerodrome are not obliged to have or use a radio. And if the aerodrome is just a lake somewhere or someone's hayfield then I don't have to make calls, but I can, using the the standard aerodrome frequency of 123.2. In any of these cases there may be someone on the frequency who will give me information. The people who run the fuel truck may reply, e.g. giving me the wind direction and telling me that there's a NORDO ultralight doing left hand circuits on 34.

Whichever kind of airport you depart from, you can enter airspace controlled by terminal or centre controllers. They usually work in darkened rooms, sometimes in the same facility as a tower, so they can share infrastructure like maintenance and backup power. If I have an emergency I can report it to any ATC or FSS I am speaking to, and they will help me coordinate with other facilities to get vectors, firetrucks, whatever I need. Canada has excellent air traffic services, and they are hiring.

And for the pilot geeks: User Friendly. My cockpit overhead light isn't working, but I didn't ground the airplane, because it's light out enough all the time that I dont' need it.


Sir Lukenwolf said...

Depending on how far north you are, you might not ever need a overhead light, although in the winter it could pose a serious problem :-)

Anyway, excellent article and a good insight to how ATC works up there, thanx for sharing.

Cirrocumulus said...

In the 1980s I saw an office humour item "Engineer's Guide to Pilots" that listed types A to F according to why they did it, what they were likely to break, why you wouldn't date them, etc.
Has anyone seen it, or a descendant, on the web anywhere?