Alternate Reality

I just received my January copy of the so-so IFR Refresher, and I came to an article “Choosing Wisely” about picking IFR alternates. IFR flying, I think, is 20% about flying and navigating the plane on instruments and 80% about memorizing obscure rules, and the IFR alternate airport rules (for choosing an alternative airport in advance, in case weather keeps you out of your destination) illustrate that point nicely. They also show some of the differences between flying in Canada and the US — I will admit to flying in the US without really knowing all of their alternate rules, and I’m sure that my fellow pilots from the US have done the same in Canada.

In Canada, if you file IFR, you have to file an alternate. Period. It doesn’t matter if every airport within 500 miles of your route is forecast to have blue skies and 50 mile visibility for the next week. In the US, sometimes you have to file an alternate and sometimes you don’t. In the US, a pilot can skip filing an IFR alternate if

  1. the destination airport has an instrument approach; and
  2. the forecast ceiling at the destination is at least 2,000 feet and the forecast visibility is at least three statue miles from one hour before to one hour after the ETA.

But wait, that applies only if you’re a US Part 91 operator. If you’re a US Part 135 operator, the ceiling requirement is different: you have to add 1,500 feet to the lowest circling minimum altitude, or if none is available, to the lowest straight-in minimum altitude, then round up to at least 2,000 feet.

Is there any benefit to this extra complexity? The main problem with alternates is fuel: in both Canada and the US, you have to carry enough fuel IFR to fly to your destination, do a missed approach, fly to your alternate, do a missed approach, and then fly 45 minutes more. In a small plane with, say, a 600 nm range, you’re not going to be able to fly too far if your closest usable alternate is 200 nm from your destination. Not filing an alternate lets you file IFR and land with a smaller fuel reserve.

If the weather is bad, though, you may still need to pick a far-away alternate to get into a different weather system, so you’re back to the fuel problem. If the weather is good at your destination, then you can just pick an alternate airport nearby (my usual good-weather IFR alternate is Gatineau [CYND], a few minutes from my home airport, Ottawa/Macdonald-Cartier [CYOW]). In the end, then, I think this benefit is more imaginary than real. I’ll just stick with always including an alternate in my IFR flight plan, in Canada or the US.

There are many other finicky differences between the Canadian and US alternate rules, but those can wait for a future posting.

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About David Megginson

Scholar, tech guy, Canuck, open-source/data/information zealot, urban pedestrian, language geek, tea drinker, pater familias, red tory, amateur musician, private pilot.
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3 Responses to Alternate Reality

  1. Pingback: Quoderat » Wikipedia URLs as blog subject codes

  2. Frank Ch. Eigler says:

    The legalities of choosing alternates are much less interesting than the practicalities.
    If the weather is down, then you had better carry enough fuel to get to a practical backup airport. If your airplane can’t carry enough fuel/payload for that trip, it is unwise to attempt it, even if a legally satisfactory alternate is available, and much less if the nearest real alternate is 200 nm away. I would not want to be in a smallest bugsmasher more than 200 nm from the nearest several airports anyhow.

    On the other hand, if the weather is so good that arrival at your destination is not at risk, then it’s probably easy VFR in the whole area. In this case, any old nearby airport can be a legal IFR alternate, and you don’t have to worry about much extra fuel.

    Or you could file a composite IFR/VFR flight plan to some intermediate point where an IFR alternate is still nearby (for legality). Once there, lose IFR and reserve requirements for the remainder of the trip and go the scenic route.

    Still, such nickel & diming with fuel reserves is uncomfortable. (That’s why I fly an airplane with 6-hour legs with a big payload.)

  3. David Megginson says:

    I agree entirely with Frank — cutting it tight with fuel never makes sense, but especially not in IMC. One point worth noting is that where Frank and I live, near the Great Lakes, IMC can sometimes be very localized. Once I was flying past (not into) Kingston, on the north short of Lake Ontario. I was in CAVU, which continued until halfway down runway 19 at the airport, after which it was solid fog and well below IFR minima. The fog bank slowly rolled down the runway back over the lake as I flew past. I’m sure that Frank has seen the same thing in his home base at Toronto Island (in fact, I once flew out of Toronto when the island was VFR, but downtown Toronto was IMC — the low clouds stopped precisely at the lake shore).

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