15 March 2008

Uncontrolled Airport arrival - Joining the circuit...

circuit joining aim Quoted here is the kind of sloppy work in the TC AIM that really bugs me, in the section on traffic circuit procedures uncontrolled aerodromes it says, "...once the pilot has ascertained without any doubt that there will be no conflict with other traffic entering the circuit or traffic established within the circuit, the pilot may also join the circuit on the downwind leg (Figure 4.6)."  My problem is that the statement quoted above and and as repeated in figure 4.6 are misleading at best and conflict with the CARs at its worst. Also, transport's authors use the word "conflict" which is not defined, but I take it to mean likely risk of collision with known traffic.

First, the statement and figure seem to suggest that in spite of any conflicts, one can enter the circuit with impunity from the upwind side as shown in figure 4.6  above? Not! The CARs clearly require one to ensure that one will not risk a collisions with other traffic (CAR 602.96) no matter how one chooses to join the circuit. Also, I doubt that the rules right-of-way (CAR 602.19) are made void by CAR 602.96.

In my view pilots doing circuits should give way to traffic joining straight in to the downwind by extending their climb straight out a little farther from the airport for separation. If there is traffic on downwind and they turn crosswind they risk collision with that traffic (thereby contravening CAR 602.19). I believe it is better to climb straight out farther from the airport for separation than it is to ultimately extend the downwind leg far past the airport because of traffic ahead. Check the midair at Mascouche in 1997 where the downwind legs stretched outside the airport's five mile zone. If someone is 5 miles from the airport they are on a cross country not the downwind leg!


If on the other hand the airport has a right hand circuit, then traffic established on downwind will have any traffic arriving from the upwind side on their right. If they collide who had the right of way? You got it the guy joining from over head is on the right of the pilot on downwind and has the right of way.

I see nothing in the CARs that say traffic established in the circuit can ignore the rules right-of-way. What the CARs say to me is that arriving traffic must avoid collisions and conform to the pattern of other traffic. They do not say don't give way to aircraft on your right when in the circuit. Also keep in mind that the CARs require all pilots to avoiding having collisions (CAR 602.19) in spite of who has the right of way.

Here is a summary of what the CARs (CAR 602.96) say about operating an aircraft on, or in the vicinity of an aerodrome (controlled or not). These are my words not the CARs.

  • Before landing or taking off the pilot must be satisfied that there will be no risk of collision with other aircraft or vehicles. And that the aerodrome is suitable for his intended operation.
  • The pilot must observe the traffic circuit so as to avoid a collision.
  • The pilot must conform to or avoid the circuit made by other aircraft operating at the airport.
  • The pilot must make all turns to the left when in the circuit, unless a right hand circuit is specified in the Canada Flight Supplement (CFS).
  • The pilot should, if able, land or take off into the wind.
  • The pilot must maintain a listening watch for air traffic control communications or if unable watch for visual signals. (As I read them the CARs do not require radio equipped aircraft to monitor the ATF.)
  • If at a controlled aerodrome the pilot must have a clearance to land, take off or taxi.
  • If not intending to land the pilot must be at least 2000 feet above the aerodrome elevation when over flying it.

No where do the CARs say one must join the circuit from the upwind side or on the downwind leg or from anywhere in particular. Nor do the CARs relieve pilots of their right of way obligations under CARs 602.19.

Let me state it quite simply, Transport Canada's statements in the AIM  about avoiding conflicts when joining the circuit on the downwind leg, appear to apply to all situations when joining the circuit, not just joining on the downwind leg as depicted in figure 4.6.

Good airmanship suggests we follow the circuit joining procedures that TC lays out in the AIM, but they should fix the wording to reflect the CARs more closely.  We are better off if we all follow known procedure--it is better to know what the other guy is likely to do and vice versa.

Michael Shaw



Adam Hunt said...

Hi Mike:

You are quite right here. The AIM and its predecessor the TC AIP contains a lot of personal opinion using words like "should" and "shall" about joining and flying in the circuit at uncontrolled aerodromes that makes it sound like it is quoting regulations.

The problem, as you have quite correctly pointed out, is that the CARs do not say agree with the AIM.

The CARS have very little to say about circuits at uncontrolled aerodromes at all. Everything that there is written about operations are uncontrolled aerodromes is in CAR 602.96 and it doesn't say much.

For instance the AIM says circuits shall normally be 1000 feet AAE. The CARs don't mention circuit height anywhere, or even say what a circuit is.

I have seen airport operators ask to TC for an exemption to allow ultralights to fly a 500 foot circuit and had TC tell them that they can't!! My response was "exemption to what?"; "denied on the basis of what?" and "if you just did it what reg would you be breaking?"

You can't be violated for breaking the "rules" laid out in the AIM.

There is no reg on how to join a circuit or how not to. There is also no prohibition on joining downwind from a 45 degree leg.

I have long thought that the AIM section on aerodrome operations should be scrapped and a new one written that conforms to the CARs, instead of giving what the author thinks is "useful advice" masquerading in the language of regulations.

Adam Hunt said...

Mike Shaw has taken his disagreement with what the AIM says on this issue one step higher and has a letter on the subject printed in ASL 4/2009.

It looks like he has ASL editor Paul Marquis' attention on the subject, as Marquis replied: "Thank you for writing to us. Your comments are appreciated and will be considered in an upcoming revision of the TC AIM. —Ed."

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Michael Shaw said...

I made similar comments to TC CAIRS suggesting that they amend the entry in the AIM. Below is their response.

Dear Mr. Shaw:

First of all, I would like to apologize for the delay in responding to you, but rest assured that your concerns were being seriously looked at and were discussed extensively here in the Department. As you are aware, those concerns, specifically circuit joining procedures described in the TC AIM, were entered into the Civil Aviation Issues Reporting System (CAIRS) and were assigned file number QD-3412. As a result of my review of the file I would like to take this opportunity to provide you with the following information:

The CARs and the AIM, while intending in the most part to say the same thing, do in fact differ now and then, but only in interpretation. The difference occurs because the people who write the AIM are, with good and sound intention, trying to make what the CARs decree as fact and law into a document that is easy to read and understand by aviation stakeholders, especially pilots. Unfortunately, sometimes that interpretation changes what the original intent was. One should always remember that the CARs are “Regulations” and the AIM a “guide”, with portions, where the CARs are referenced, a regulation. Any time the exact wording from the CARs is changed, no matter how small or subtle the change is, it does not then truly reflect the CARs.

As a result of your concerns, please be assured that we will undertake to rewrite “TP14371 http TC AIM RAC sub 4.0 Airport Operations” to express the intent of CARs Part VI, Subpart 2 Operating and Flight Rules, Division V - Operations at or in the Vicinity of an Aerodrome.

I would like to take this opportunity to thank you for sharing your views, as all comments we receive are appreciated.


Ron Carter
Chief of Standards / Chef des normes
Aerodromes and Air Navigation / Aérodromes et navigation aérienne Telephone / téléphone: (613) 998-9855 Facsimile / télécopieur: (613) 954-1602 TTY / ATS (613) 990-4500 ron.carter@tc.gc.ca Transport Canada | Place de Ville (AARTA), Ottawa, Ontario K1A 0N8 Transports Canada | Place de Ville (AARTA) Ottawa (Ontario) K1A 0N8 Government of Canada | Gouvernement du Canada