Frost, cloud and three miles: the Canadian weather limits that stop a winter job

Three miles, and clear of cloud

The Canadian Aviation Regulations set a weather floor for beyond visual line of sight work that has nothing to do with how good the camera is. Unless a specific allowance applies, the operation requires ground visibility of at least three miles and the aircraft must be flown clear of cloud. Ground visibility is the measure, observed at the surface. It is not the view from the aircraft and it is not flight visibility, which is the mistake crews make when the downlink looks clean on a morning that is socked in at the launch site. There is an allowance, and it is the reason the weather line belongs in procurement rather than in a folder of rules. A pilot may operate in cloud or below three miles of ground visibility where a safety assurance declaration has been made for that aircraft model against the relevant Standard 922 requirements and the operating manuals allow for the conditions, or where a Special Flight Operations Certificate covers the operation. Visual line of sight has its own arithmetic. For a medium remotely piloted aircraft, when ground visibility is four miles or less, the aircraft cannot be flown further than half that distance unless an SFOC covers it. For crews flying aircraft between 25 and 150 kilograms, that single sentence can decide how much of a corridor is workable on a marginal morning.

Frost and ice are not a judgement call Cold weather adds a harder limit.

Where icing conditions are observed, reported or likely along the route, flight is not permitted unless the aircraft carries de-icing or anti-icing equipment, or the person flying it has some way to detect icing. Separately, an aircraft with frost, ice or snow adhering to its critical surfaces cannot be flown at all, and critical surfaces include the rotors, propellers, control surfaces and stabilising surfaces. For Canadian field work the sequence is what matters. An aircraft moved from an unheated trailer into a warmer, humid layer, or a set of batteries that spent the night in a truck, is how frost arrives on a propeller without anyone noticing it. The regulation puts the check before the launch, not in the air, and the check has to be written into the pre-flight rather than left to habit.

Night is a lighting requirement, not a prohibition Night operations are permitted with equipment conditions.

The aircraft must carry lights sufficient to keep it visible to the pilot or a visual observer, and those lights must be switched on. With the daylight window collapsing through the autumn, night capability is often the difference between completing a programme on schedule and carrying the balance into spring, so lighting, any night endorsement on the crew, and the weather limits all belong in the same review.

What weather actually costs

The expensive part of a Canadian weather limit is not the aircraft, it is the schedule. A stood-down day still carries crew time, mobilisation, site access and a client expectation, and on a pipeline or plant job it can cost a shutdown window that cannot be recovered until the next planned outage. The crews that handle it well treat the decision as a gate: one named person, one call time the evening before, and a forecast read for the specific site rather than for the region.

The operational takeaway Write a one page weather card for every aircraft type in the fleet.

Put the ground visibility minimum on it, the cloud clearance requirement, whether a declaration or an SFOC widens the envelope, the icing equipment status and the frost procedure, the night lighting configuration, and the name of the person authorised to stand the crew down. Review it at the start of the heating season, not on the first marginal morning of the winter.