What weather can I fly in?

Know the weather conditions section 901.34 permits for a VLOS and a BVLOS operation, know which of them an SFOC can change, and know the one environmental requirement that a VLOS flight is excused from. AIM 3.6.1

The minimum weather rules for remotely piloted aircraft are not the same as those for other aircraft, and section 901.34 is short enough to be read in full. It is also drafted so that its second and fourth subsections carry the numbers, which is where a reader skims. CAR 901.34

• You know whether the operation is VLOS or BVLOS, because the two have different tests. CAR 901.34
• You know the operating manuals for your system, because both the VLOS test and the BVLOS exception to it are decided partly by what those manuals allow. CAR 901.34
• You know whether the aircraft is medium or small: only the medium case carries the ground-visibility rule in subsection (2). CAR 901.34

No pilot shall operate a remotely piloted aircraft to conduct a VLOS operation unless the weather conditions at the time of flight permit both: the operation to be conducted in accordance with the operating manuals, and the pilot or any visual observer to conduct the entire flight in visual line-of-sight. CAR 901.34

The words "entire flight" are doing the work. A visual observer who can see the aircraft at the start and loses it in a rain shower halfway through does not satisfy the condition, and the test is applied to the flight, not to the take-off. CAR 901.34

If the ground visibility is four miles or less, no pilot shall operate a medium remotely piloted aircraft in a VLOS operation at a distance of more than half the ground visibility unless the operation is conducted in accordance with a special flight operations certificate — RPAS. CAR 901.34

Two things make that rule easy to misapply. It is measured against ground visibility, which is a reported value, not what the pilot can see from where they stand; and it applies only to a medium aircraft, so a small one is not caught by it. CAR 901.34

Subject to subsection (4), no pilot shall operate a remotely piloted aircraft to conduct a BVLOS operation unless ground visibility is not less than three miles and the aircraft is clear of cloud. CAR 901.34

Note that the baseline is a floor and a state: three miles, and no cloud. Both have to hold. CAR 901.34

A pilot may operate BVLOS in cloud or when ground visibility is less than three miles if either: a declaration under section 901.194 has been made in respect of the model and of the technical requirements set out in section 922.10 of Standard 922, and the operating manuals applicable to the system allow operation in those conditions; or the operation is conducted in accordance with a special flight operations certificate — RPAS. CAR 901.34 Std 922.10

The first route is the one that surprises people: operating BVLOS in cloud is not a pilot-judgement decision, it is a declaration question, and the declaration has to cover the technical requirements the section names as well as the model. CAR 901.34

Compliance with section 922.12 of Standard 922 — the demonstrated environmental envelope — is required for all BVLOS operations that are within 1 km of populated areas, or over sparsely populated areas. It exists so that a system used for those operations has a well-defined flight envelope demonstrated through flight test. Std 922.12

It is not required for VLOS operations, and the standard says why: in a VLOS operation visual contact is maintained with the aircraft, so the observer can see when it is being adversely affected by environmental conditions. The requirement keeps the aircraft close enough to the nearest observer that the conditions at the observer are the conditions at the aircraft. Std 922.12

That is a statement about what VLOS is, not a concession — and it is why a VLOS pilot cannot borrow the reasoning for a BVLOS flight. Std 922.12

Sufficient weather conditions must be present to ensure the aircraft can be operated in accordance with the manufacturer's instructions — temperature, wind, precipitation and the rest — and to allow the pilot or a visual observer to keep it within VLOS at all times. AIM 3.2.22

Weather information comes in different forms for different time scales, from climate normals through forecasts to real-time conditions, and choosing the right one is part of the planning. AIM 3.2.22

AIM RPA 3.4.2.3(f) sets the weather conditions for a level 1 complex operation, as per CARs section 901.34 — the ground visibility is not less than 3 NM, and the aircraft is operated clear of cloud. It is the same formulation the VLOS rules use, applied to the highest-risk operation in the regulations, and it sits in a list of conditions that must all be met before commencing: fly in uncontrolled airspace only (901.87), at or below 400 ft AGL (901.25), more than 5 NM from the centre of aerodromes listed in the CFS or CWAS (901.47), be familiar with the flight information including the site survey's distance from populated or sparsely populated areas (901.24, 901.27(h)), any safety assurance declaration for the model (901.194), the crew's qualifications, have the operations manual immediately available (901.30), and carry anti-collision lights turned on (901.38.1). AIM 3.4.2

The AIM adds a fact that matters to any operation at altitude: an RPAS flies in air whose temperature falls as it climbs, because the pressure falls. That is the adiabatic lapse rate, and the AIM gives two standard values — 3 °C per 1 000 ft (about 9.8 °C per 1 000 m) in unsaturated air, and 1.5 °C per 1 000 ft (about 4.9 °C per 1 000 m) in saturated air. AIM 3.2.22

Read the arithmetic off those numbers, because a question can: starting from 20 °C at the surface, air at 2 000 ft in unsaturated conditions is about 6 °C cooler — 14 °C. AIM 3.2.22

Two qualifications come with the rates. Water vapour reduces them — moist air cools more slowly, because latent energy is released as it condenses — and the published values are standard rather than actual, so the real rate varies with the water content of the air column. AIM 3.2.22

That is why the AIM raises it in a weather section at all: on a high-altitude flight the temperature in the forecast for the surface and the temperature the aircraft meets can differ a great deal, and a demonstrated environmental envelope is a temperature envelope as much as anything else. AIM 3.2.22

Situation	What applies
VLOS, any weather	The manuals must permit the operation and the flight must be in VLOS for its entirety CAR 901.34
VLOS, medium aircraft, ground visibility 4 miles or less	No more than half the ground visibility, unless under an SFOC CAR 901.34
VLOS, small aircraft	Subsection (2)'s ground-visibility rule does not apply CAR 901.34
BVLOS	Ground visibility not less than 3 miles, and clear of cloud CAR 901.34
BVLOS in cloud or under 3 miles	A declaration covering the model and section 922.10, with manuals that allow it — or an SFOC CAR 901.34
BVLOS within 1 km of populated areas, or over sparsely populated areas	A demonstrated environmental envelope under section 922.12 Std 922.12
VLOS operations	Section 922.12 is not required Std 922.12

Warning "The weather looked fine from where I was standing" answers a different question from the one 901.34 asks. Subsection (2) is measured against ground visibility, and subsection (1) requires VLOS for the entire flight — not at the point of take-off, and not at the point where the pilot last had a clear view. CAR 901.34

Symptom	Likely cause	What to do
Your visual observer lost the aircraft mid-flight	Subsection (1) requires VLOS for the entire flight	End the VLOS operation; the condition has failed CAR 901.34
You flew a medium aircraft 400 m in 3-mile visibility	The limit is half the ground visibility	Stay within half, or operate under an SFOC CAR 901.34
You flew a small aircraft in the same conditions and assumed the same rule	Subsection (2) names medium aircraft only	Check the class before applying the rule CAR 901.34
You want to fly BVLOS in cloud	The baseline requires clear of cloud	You need the declaration (covering 922.10) or an SFOC CAR 901.34
Your manuals do not cover the conditions	The BVLOS exception requires the manuals to allow them	Do not rely on the declaration alone CAR 901.34
You are planning BVLOS near a populated area	Section 922.12 applies	Confirm the demonstrated environmental envelope Std 922.12

Practise: Weather minima for RPAS operations

Practise: Weather lapse rate

• CAR 901.34 — Minimum Weather Conditions
• Standard 922 s.922.10 — Detect, Alert and Avoid Systems
• Standard 922 s.922.12 — Demonstrated Environmental Envelope
• AIM RPA 3.2.22 — Minimum Weather Conditions
• Consolidation: CARs current to 2026-09-21