From Principal Air LTD.

Late on the morning of May 16, 1999, two C-172s approaching to land on runway 32 at the 108 Mile Airport (CZML) found themselves in the same piece of air at the same moment.

At approximately 300’ above the ground, the aircraft slammed into one another, and, locked together, descended steeply onto the corner of a warehouse building at the south end of the runway.

Three people were involved in the crash; all sustained serious injuries.

According to the Transportation Safety Board of Canada (TSB) report, A99P0056, the mid-air collision, one of six similar crashes which have occurred in the vicinity of uncontrolled aerodromes between August 1989 and August 1999, resulted from a series of causes and contributing factors.

Neither pilot saw the other prior to the collision nor took any avoidance action.

One of the aircraft was flying a left-hand circuit pattern for runway 32; the runway has a published right-hand pattern. The other aircraft was flying a straight in approach to the same runway.

One aircraft was broadcasting on a handheld radio, apparently tuned to the wrong frequency. The other aircraft’s radio was being handled by the passenger; the pilot was not using a headset.

Neither aircraft was using all available aircraft lighting systems to increase visual conspicuousness.

Working out of an uncontrolled aerodrome offers a number of advantages, and, of course, a few disadvantages. Uncontrolled aerodromes offer an environment that strongly promotes self-reliance and stresses the importance of maintaining a keen situational awareness at all times. Working in this type of environment, even part of the time, helps pilots realize and appreciate how important it is to be alert and aware.

Keeping everyone safe in an uncontrolled traffic pattern depends on the knowledge, skill and good will of pilots using the aerodrome. As the AIP section RAC 4.5.1 reminds us, “There is no substitute for alertness while in the vicinity of an uncontrolled aerodrome.”

Sitting on the ramp watching traffic at my home base, Chilliwack (CYCW), on an average weekend, it’s apparent that a significant number of pilots are either unfamiliar with the published approach, circuit and departure procedures, or are all too willing to put their lives and the lives of fellow aviators in jeopardy, trusting to the angels who look after those who take to the skies.

I think we can do better; I think we can invest the few moments it takes to check our Canadian Flight Supplement (CFS) before visiting a new aerodrome, learn and practice published procedures and be part of the solution leading to aviation safety for all of us.

For quick reference, section RAC 4.5 in your AIP provides generic information regarding procedures and practices for uncontrolled aerodromes.

For information about a specific aerodrome or airport, consult your CFS. And, finally, a check on applicable weather and Notam information can be obtained through a call to your friendly, local Flight Service Station (FSS) immediately before a flight.

I still remember doing a cross country flight as a student pilot and arriving at a small aerodrome that was in the midst of a radio controlled airplane meet; I had been so keen to get going, I’d neglected to check Notams.


So, what do we learn when we consult our AIP regarding uncontrolled aerodromes? We learn that uncontrolled aerodromes are classed into three groups: Those with a Mandatory Frequency (MF), where there is someone on the ground who responds to radio calls. Those designated ATF, where pilots communicate with the “traffic”; and those smaller aerodromes without a published frequency, either MF or ATF, which normally use the common frequency 123.2 MHz.

Check your CFS for specific information.

At MF aerodromes, the ground station normally provides wind traffic, runway and altimeter data. Some ATF aerodromes have an automated Voice Generator Module (VGM) AWOS broadcast facility which provides continuous weather and altimeter data.

Many smaller aerodromes have no such facilities, and pilots must rely on first hand observation to determine wind, weather conditions and the runway in use. It is important to remember that ATF and unpublished frequency aerodromes may be used by aircraft operating without a radio (NORDO) or with receive-only capability (RONLY) so pilots must remain alert to traffic not reporting positions or responding to radio calls.

At aerodromes where a Mandatory Frequency (MF) is in effect, aircraft must be equipped with a functional two-way radio and reporting procedures must comply with CARs 602.97 to 602.103 inclusive.

Pilots of radio-equipped aircraft operating at ATF or unpublished frequency aerodromes are expected to engage in appropriate communication procedures, both on the ground and in the air, to ensure there are no conflicts with other aircraft.

Normally, on arrival, this will involve reporting before entering the zone, at mid-field, on joining downwind, on final approach and clear of the active runway (CAR 602.101). On departure, radio calls should be made before moving the aircraft on the ground, before entering the active runway and when clear of the zone (CAR 602.100).

In the circuit, calls should be made on downwind and on final approach (CAAR 602.102). The appropriate radio frequency should be monitored when in the vicinity of the aerodrome, remembering non-radio-equipped aircraft may be operating in the area (CAR 602.103).


Let’s talk about traffic circuit procedures. This seems to be an area where some work could be done. Many pilots used to operating at controlled airports where traffic is closely monitored by a tower may not be used to looking out so carefully for other traffic or maintaining the situational awareness so necessary in an uncontrolled environment.

They may not be used to the discipline of following an approach or departure procedure on their own initiative. When approaching an uncontrolled aerodrome designated as ATF or operating without a published frequency, pilots are expected to approach and land on the active runway. The active runway is the runway in use or the runway aircraft are intending to use.

Before committing to a particular runway, make certain you know which runway is currently in use. If you choose not to land on a currently active runway, you must wait until the pattern is clear of other aircraft before changing the active runway.

Many small aerodromes have flight training activities of some description: agricultural training or fire suppression training, for example. The prevailing wind may not be the only consideration in choice of runway. If no other aircraft are using the circuit, a pilot on approach may select which runway he or she would prefer to sue under existing conditions. The AIP (RAC 4.5.2) reminds us that, “Should it be necessary for an aircraft to approach, to land on, or take off from a runway other than the active runway, it is expected that the appropriate communication will take place to ensure there is no conflict with other traffic.”

The AIP also stresses the importance of “personal airmanship” and courtesy.

The default circuit is a left-hand pattern. However, for a variety of reasons, a particular aerodrome may have a right-hand pattern for a particular runway.

Chilliwack, for example, has a published right-hand pattern for runway 06 and a standard, left-hand pattern for runway 24 to reduce the noise and potential danger of having aircraft flying circuits over the city.

It is important to check your CFS before arriving at a strange aerodrome so you are certain of the correct procedures. An aircraft flying a left-hand circuit for a runway with a published right-hand pattern – how many times have we seen that? – creates a very dangerous situation.

Unless otherwise published, circuits are flown at 1000’ Above Aerodrome Elevation (AAE).

Normally, landings and take-offs are performed on the runway most nearly facing into the prevailing wind; however, it is the pilot’s responsibility to determine which runway is the safest under prevailing conditions.

Some aerodromes are one-way due to obstacle, terrain or slope conditions. During early morning or late afternoon, it may be safer to land or take-off with your back to the sun, even if you do have a slight tail wind.

Unless otherwise specified in the CFS, aircraft should approach the traffic pattern from the upwind side, cross mid-field at circuit height and join the appropriate downwind. This is by far the safest plan of action.

Crossing mid-field at circuit height from the upwind side provides an excellent opportunity to check out the runway(s), any ground traffic that may be a factor, and to locate traffic in the circuit.

It also makes it much easier for traffic in the circuit to see and be aware of you. (See Figure 1)

If a pilot has determined without doubt that it is safe to do so and will not result in a conflict situation, he or she may join the traffic pattern on the downwind leg.

The emphasis here is safety; if there is any possibility of coming into conflict with aircraft already in the circuit or with aircraft joining the circuit from the upwind side, the downwind entry should be avoided.

Remember, simply making a radio call is not sufficient: NORDO and RONLY aircraft may be operating in the circuit and will not be able to respond.

It is also acceptable, should it be necessary, to cross over the aerodrome from the downwind side to initiate a mid-field crossing from the upwind side.

It is recommended that this crossover be performed at a minimum of 500’ above circuit altitude (AIP RAC 4.5.2aiii). I can say categorically, from personal experience, this is not a very safe procedure.

While correct in theory, pilots in the circuit are not always as careful about maintaining correct altitude as we might hope. In almost all cases, it is safer to plan your approach to an aerodrome so you may enter the pattern from the upwind side without having to cross over first.

If you must cross over the aerodrome, 2000’AAE is a safer altitude to ensure no conflict with aircraft in the circuit.

All descents to circuit altitude must be made on the upwind side well clear of the aerodrome so the mid-field crossing may be accomplished at circuit height. Under no circumstances should an aircraft descend or climb to circuit height while in the circuit.

At MF aerodromes where airport advisory information is available from the ground station, additional approach options exist. Pilots may join the circuit pattern straight in or at a 45 degree entry to the downwind, as appropriate, in addition to the approach patterns used at ATF and unpublished frequency aerodromes.

This in no way reduces a pilot’s responsibilities to avoid conflict with other traffic and to remain alert and aware of other traffic in the area. (See Figure 2)

Departures from uncontrolled aerodromes are somewhat different from the procedure used at controlled airports, as well.

Unless an aircraft is remaining in the circuit, it must climb on runway heading to a minimum of circuit altitude before initiating a turn in any direction.

How many, many times have we seen aircraft become airborne and immediately initiate a turn towards their destination, creating a potentially very dangerous conflict with other aircraft that may be in the circuit.

Before turning back towards the aerodrome, an aircraft must climb to a minimum of 500’ above circuit altitude (AIP RAC 4.5.2c). For aircraft remaining in the circuit, a climb to circuit altitude before turning downwind is required (AIP RAC 4.5.2b).


Visiting and using uncontrolled aerodromes can enrich and develop a pilot’s repertoire of skills and experience and extend his or her opportunities to see and experience new and different aviation environments.

Some of the most beautiful, interesting and inviting destinations are available to pilots making use of uncontrolled aerodromes.

The key to safety at uncontrolled aerodromes is simple: learn and use the correct procedures, become familiar with all the necessary particular information about the aerodrome you intend to visit and remain alert and situationally aware at all times.

Your life, the lives of your passengers and the lives of other pilots in the area depend on your knowledge and skills.

Aviation safety is something we each build, one flight at a time.

Another Interesting article on uncontrolled airport collisions may be found here.