The weather at the airport is reported below minima — is it legal to try the approach anyway, just to take a look, before heading to your alternate? This is one area where the rules in Canada and the U.S. seem to differ quite a bit.
In the U.S., aircraft operating under FAR Part 91 (private and some commercial operations) have no restriction at all: they are free to try an approach even if the weather is reported as 0 ceiling and visibility. U.S. aircraft operating under FAR Part 135 (charter and commuter, sort-of) are not allowed even to attempt an approach unless the weather is at or above minima. This is probably a gross oversimplification, but it gets the rough idea across.
Canada falls somewhere in between these two extremes. We have something called the Approach Ban, laying in out gory detail when the pilot of any flight (private or commercial) is allow to attempt an approach based on Runway Visual Range (RVR) reports from transmissometers located at the runway threshold (RVR “A”) and mid-runway (RVR “B”):
- When only RVR “A” or RVR “B” is available for the approach runway, it must be reporting at least 1,200 ft.
- When RVR “A” and RVR “B” are available for the approach runway, RVR “A” must be reporting at least 1,200 ft, and RVR “B” must be reporting at least 600 feet for fix-wing aircraft (any value is OK for rotorcraft).
If these conditions are not met, then an aircraft is not allowed to complete an approach past the outer marker or final approach fix. There are a whole bunch of exceptions, though:
- if the aircraft is already inside the OM or FAF inbound when it receives the report, it may continue;
- if the aircraft has informed ATC that it is on a training flight and plans to go missed, it may continue;
- if the RVR is fluctuating above and below, and the reported airport visibility is at least 1/4 SM, the aircraft may continue; and
- if the aircraft is conducting a CAT III approach, it may continue.
Even more importantly, the ban applies only to airports operating transmissometers on the approach runway — if you’re flying into a medium or small airport, or even approaching a smaller runway at a big airport, there are usually no transmissometers, and therefore, no approach ban.
That said, as far as I understand (never having sat through commercial ground school), commercial operations all have Transport-Canada-approved operating manuals that can place additional restrictions on what pilots flying for the operator are allowed to do, and these may go far beyond the approach ban (especially since they’re usually ammended after every an accident or incident).
Corrections and elaborations are welcome in the comments, especially from pilots who have sat through commercial groundschool on either side of the border.
Land and Hold Short 
Since there are such hard and fast rules about these approach bans, do they announce it on the ATIS or refuse to grant approach clearances when they are in effect?
They include the RVR on the ATIS once the visibility drops to a certain level — I’m not sure what that level is, though. You don’t hear it very often here, but I’ll be that you would in Halifax. I’ve never flown into an airport below 400 ft/1 SM, so I don’t know what happens if someone wants to do an approach when the weather’s down; I imagine that ATC would give you the clearance anyway (after dropping some heavy hints), since their job is just to separate traffic, not to police it.
When I left Ottawa for a Hope Air flight last month, two jets went missed to Mirabel, but that was because of low ceiling rather than visibility so the RVR wasn’t governing and the approach ban wasn’t in effect.
The approach ban rule also exists in Europe and applies to all aircraft including the military. At a well equipped airport the minimum RVR is usually about 600m for an ILS. You are not allowed to make an approach to land if the RVR is below this figure. If uyopu insist on flying the approach into a British cicil airport the controller will say: ‘The action you are taking appears to contravene current legislation – a report will be made’. They will not actually turn out the lights! The relevant minima are on the approach plates so if the VOLMET or ATIS says the RVR is 400m you know you will not be allowed to attempt the approach. There is not even a cheat where you say that you are making a training approach to go around and then, when you see the approach lights you cancel IFR and continue visually because the approach ban also applies to visual approaches. This is to cater for the shallow fog case where you can see the ground from high up but you lose references during the last part of the approach. Most JAR states have this rule but some others(eg Canada) exempt the military. I was, however, interested in your statement that the equivalent rule does not apply to private pilots in the US. I am not familiar with the various FAR Part numbers which define the different rule structures for private, commuter or public transport categories. As it happens, I am doing some research for the British military who are not sure which rules apply to them when flying into military airports in the US (or Iraq). Would you email me with what you perceive to be the relevant FAR Part numbers?
Thanks
George Morris
(private flying instructor and military simulator instructor, former military pilot)
Thanks for the comment, George. In the U.S., FAR 91.175 contains general regulations for IFR approaches, while FAR 135.225 contains additional regulations for charter and commuter flights. There is no approach ban in 91.175, while there is one in 135.225.
Thanks for that. The regulation appears to be written in Martian, but I think I have the gist of it! Although there is no approach ban rule as such it seems that you cannot descend below DH or land unless the flight visibility is above minimum, so you haven’t gained much.I appreciate that there are subtle differences between reported visibility and in flight visibility, but where the minimum for the approach is defined as an RVR surely there can be no scope for continuing an approach below DH when the RVR is below minimum, can there?
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