Temp's and QNH's in a TAF
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If you are using an area forecast as there is no TAF available then the criteria required at the destination are VMC. Would it not then be possible to overfly and look at the windsock and isn't that what "they" expect you to do?
The biggest problem with using an area forecast is deciding if your destination is in a particular area used in the forecast eg. on the western slopes or on the ranges south of xxx. Can become sticky.
It's ok to say just plan for an ALT if in doubt but sometimes fuel and weight become a big issue and out west it's a long way to another destination that does not require an ALT. I know of quite a few aerodromes without TAF service but they have an aid or an RNAV approach.
The biggest problem with using an area forecast is deciding if your destination is in a particular area used in the forecast eg. on the western slopes or on the ranges south of xxx. Can become sticky.
It's ok to say just plan for an ALT if in doubt but sometimes fuel and weight become a big issue and out west it's a long way to another destination that does not require an ALT. I know of quite a few aerodromes without TAF service but they have an aid or an RNAV approach.
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patienceboy,
You missed the point of my question. You seem to be missing the point of most things and not thinking critically about what is before you.
Yes, the heading to that passage (57.2.12) implies that what follows is purely about alternate minima, but then you get to section (b) and you find that that section is not actually about alternate minima.
Sections (a) and (c) cover all the possibilities (all two of them) for IFR flight. Section (b) does not contribute anything at all relating to alternate minima.
Section (b) does not need to be there, and the question of why it is there is irrelevent.
But what is relevent is the implication carried by the words of (b).
According to you - a believer that "NO TAF = ALTERNATE" - the words "with an instrument approach" are in that section by error. Here is that section again, this time with the erroneous words (according to you) highlighted in red:
b. For aerodromes with an instrument approach procedure where an aerodrome forecast is unavailable or is "provisional", the pilot in command must make provision for a suitable alternate.
According to you, the inclusion of those words in red was an error on the part of CASA.
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Should I have said 51 NM instead of 50 NM? Ok, try this:
Under your assertion (that "NO TAF = ALTERNATE"), a VFR flight, in perfect daytime weather, to a small farm 51 NM away must provide for an alternate (because the place has no TAF (and no navaids)).
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That is NOT a list of aerodromes for which a TAF will be available.
That is a list of aerodromes for which a TAF MAY be available. For some aerodromes, the TAF coverage is not "full time" (i.e. the TAF covers daylight hours only).
If the aerodrome has a TAF during the day only, then, during the night hours, the TAF is ... wait for it ...
NOT AVAILABLE
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At long last we are getting to the logic behind the rules. I'm glad you raised this because it shows you are at last starting to think about things, rather than just reading words from a page.
It's all about the navaids.
Yes, it appears that navaid aerodromes impose greater requirements than non-navaid aerodromes but this is not actually true. In practice, the average GA pilot will carry an alternate for non-navaid aerodromes far more frequently than he will for those with navaids.
And it would probably be true to say that, in the majority of cases where the average GA pilot is carrying an alternate for a non-navaid aerodrome, he is unaware he is doing so!
An aerodrome with a navaid will tend to be one that does not require an alternate, and can be nominated as an alternate. Such an aerodrome WILL have a TAF routinely issued for it.
But the TAF may not cover the night hours. The TAF is then considered "not available" and that rule (about which we are debating) comes into play.
That rule, as we well know, is this one:
When an aerodrome forecast is not available or is "provisional", the pilot in command must make provision for a suitable alternate that has a firm forecast. (AIP GEN 57.1.3)
The logic behind the rule is about addressing the fact that, despite having an instrument approach, without a valid TAF, the aerodrome is not satisfactory as a place that can serve as an alternate for other aerodromes.
Please note that, for simplicity of discussion, I have deliberately left out runway lighting related alternate requirements.
You have to read this in conjunction with (a) and in the knowledge that it is talking purely about meteorological alternate minima.
Yes, the heading to that passage (57.2.12) implies that what follows is purely about alternate minima, but then you get to section (b) and you find that that section is not actually about alternate minima.
Sections (a) and (c) cover all the possibilities (all two of them) for IFR flight. Section (b) does not contribute anything at all relating to alternate minima.
Section (b) does not need to be there, and the question of why it is there is irrelevent.
But what is relevent is the implication carried by the words of (b).
According to you - a believer that "NO TAF = ALTERNATE" - the words "with an instrument approach" are in that section by error. Here is that section again, this time with the erroneous words (according to you) highlighted in red:
b. For aerodromes with an instrument approach procedure where an aerodrome forecast is unavailable or is "provisional", the pilot in command must make provision for a suitable alternate.
According to you, the inclusion of those words in red was an error on the part of CASA.
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No he wouldn’t. See below.
Under your assertion (that "NO TAF = ALTERNATE"), a VFR flight, in perfect daytime weather, to a small farm 51 NM away must provide for an alternate (because the place has no TAF (and no navaids)).
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Given that this is a list of aerodromes “for which a TAF will be available”, couldn’t one reasonably conclude that a list of aerodromes which don’t feature here would be a list of aerodromes for which a TAF will not be available?
That is a list of aerodromes for which a TAF MAY be available. For some aerodromes, the TAF coverage is not "full time" (i.e. the TAF covers daylight hours only).
If the aerodrome has a TAF during the day only, then, during the night hours, the TAF is ... wait for it ...
NOT AVAILABLE
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Under your interpretation we could fly to an aerodrome with multiple instrument approaches, a provisional TAF and a valid area forecast and we would require an alternate - yet we could fly to an aerodrome never issued with a TAF, no instrument approach or navaids and the same area forecast and no alternate is required. That doesn’t make sense.
It's all about the navaids.
Yes, it appears that navaid aerodromes impose greater requirements than non-navaid aerodromes but this is not actually true. In practice, the average GA pilot will carry an alternate for non-navaid aerodromes far more frequently than he will for those with navaids.
And it would probably be true to say that, in the majority of cases where the average GA pilot is carrying an alternate for a non-navaid aerodrome, he is unaware he is doing so!
An aerodrome with a navaid will tend to be one that does not require an alternate, and can be nominated as an alternate. Such an aerodrome WILL have a TAF routinely issued for it.
But the TAF may not cover the night hours. The TAF is then considered "not available" and that rule (about which we are debating) comes into play.
That rule, as we well know, is this one:
When an aerodrome forecast is not available or is "provisional", the pilot in command must make provision for a suitable alternate that has a firm forecast. (AIP GEN 57.1.3)
The logic behind the rule is about addressing the fact that, despite having an instrument approach, without a valid TAF, the aerodrome is not satisfactory as a place that can serve as an alternate for other aerodromes.
Please note that, for simplicity of discussion, I have deliberately left out runway lighting related alternate requirements.
Last edited by FGD135; 26th Mar 2011 at 06:15.
Yes, it appears that navaid aerodromes impose greater requirements than non-navaid aerodromes but this is not actually true.
b. For aerodromes with an instrument approach procedure where an aerodrome forecast is unavailable or is "provisional", the pilot in command must make provision for a suitable alternate.
So dirt strip in the GAFA with an RNAV approach but no TAF WILL REQUIRE an alternate.
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So dirt strip in the GAFA with an RNAV approach but no TAF WILL REQUIRE an alternate.
By "weather is good", I mean the forecast weather satisfies the alternate requirements, which you can find in AIP.
Last edited by FGD135; 26th Mar 2011 at 07:39.
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You missed the point of my question. You seem to be missing the point of most things and not thinking critically about what is before you.
I'm glad you raised this because it shows you are at last starting to think about things, rather than just reading words from a page.
That is NOT a list of aerodromes for which a TAF will be available.
That is a list of aerodromes for which a TAF MAY be available. For some aerodromes, the TAF coverage is not "full time" (i.e. the TAF covers daylight hours only).
If the aerodrome has a TAF during the day only, then, during the night hours, the TAF is ... wait for it ...
NOT AVAILABLE
That is a list of aerodromes for which a TAF MAY be available. For some aerodromes, the TAF coverage is not "full time" (i.e. the TAF covers daylight hours only).
If the aerodrome has a TAF during the day only, then, during the night hours, the TAF is ... wait for it ...
NOT AVAILABLE
Should I have said 51 NM instead of 50 NM? Ok, try this:
Under your assertion (that "NO TAF = ALTERNATE"), a VFR flight, in perfect daytime weather, to a small farm 51 NM away must provide for an alternate (because the place has no TAF (and no navaids)).
Under your assertion (that "NO TAF = ALTERNATE"), a VFR flight, in perfect daytime weather, to a small farm 51 NM away must provide for an alternate (because the place has no TAF (and no navaids)).
Please refer to the point I made in post 41 regarding ARFORs and meteorological alternate minima (specifically wind). How could you meet all of the requirements of ENR 57.2 without a TAF? If an ARFOR cannot be used to meet ALL of the requirements of ENR 57.2 this is all academic and you simply need a TAF – which would certainly agree with 57.1.3 at face value.
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Blacknight
Yes, that is what you might do when you arrive at the airfield. However, at the planning stage you will need to refer to a forecast to determine whether you need to load fuel for an alternate or not.
The last thing you want is to rock up to a strip in the middle of nowhere with no fuel to divert and be unable to land.
If you are using an area forecast as there is no TAF available then the criteria required at the destination are VMC. Would it not then be possible to overfly and look at the windsock and isn't that what "they" expect you to do?
The last thing you want is to rock up to a strip in the middle of nowhere with no fuel to divert and be unable to land.
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Aerodromes and Categories for which a TAF will be Available is the actual name of the list, which is why I pasted a copy and put that section of the name in quotation marks.
Are you back to just reading words without thinking, or are you raising semantics in order to obfuscate?
Given your quibble over the 50 NM vs 51 NM, I think it is the latter.
Only if his cruise speed is less than 100kt.
Please refer to the point I made in post 41 regarding ARFORs and meteorological alternate minima (specifically wind). How could you meet all of the requirements of ENR 57.2 without a TAF?
The area forecast will also allow you to glean whether the wind at your destination is such that an alternate may be required, but again, this information will not be presented directly for individual aerodromes.
If any of those are present, the ARFOR will mention it - along with enough specifics of associated wind direction and speed to make possible the assessment of alternate requirements.
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Another attempt at obfuscation. What you are referring to is a rule about whether a forecast is required for a flight, which is a totally different thing to whether an alternate is required for a particular destination.
When questioned on an ARFORs suitability for determining meteorological minima (specifically wind) you said:
For an aircraft's crosswind or downwind limits to be exceeded - on a sustained basis - there has to be some suitable meteorological phenomena in the area (or nearby). Examples of such phenomena include cyclones, tropical lows and fronts.
If any of those are present, the ARFOR will mention it - along with enough specifics of associated wind direction and speed to make possible the assessment of alternate requirements.
If any of those are present, the ARFOR will mention it - along with enough specifics of associated wind direction and speed to make possible the assessment of alternate requirements.
The winds forecast are an average for a very large area and are winds aloft – not surface winds. Local geography alone can cause winds at a specific location to be wildly different from those on the area forecast. For a light aircraft with a maximum crosswind component of 15kt, it hardly takes a cyclone to require an alternate!
The AIP also includes the words “Note: wind gusts must be considered”. Limits do not have to be exceeded on a "sustained basis". The ARFOR doesn’t give you this information. If the wind forecast at 3000ft was an easterly at 35kt, and your destination runs North/South – what will be the wind on the ground and do you need an alternate? Also refer to the ARFOR I posted earlier with a similar question re visibility.
