Temp's and QNH's in a TAF
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AIP GEN 57.1.3 (page 88 of the PDF from the web)
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.
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.
Try again.
FGD ..OK try this one.
Enroute 1.2.3
For flights to a destination for which a aerodrome forecast is required and cannot be obtained or is "provisional", the flight is permitted to depart providing an alternate aerodrome meeting all the requirements specified in ENR1.1 Section 57 is provided.
Cannot be obtained ... can also mean there aint one to get!
Now it all comes down to english interpretation .. That's what Lawyers are for ...not pilots
Enroute 1.2.3
For flights to a destination for which a aerodrome forecast is required and cannot be obtained or is "provisional", the flight is permitted to depart providing an alternate aerodrome meeting all the requirements specified in ENR1.1 Section 57 is provided.
Cannot be obtained ... can also mean there aint one to get!
Now it all comes down to english interpretation .. That's what Lawyers are for ...not pilots
FGD 135...
Got to agree with Icarus and Agent - and I have run up against this in the past. The argument "well most pilots don't do that" or "there's never a TAF for there, so use the ARFOR", or something else that sounds similar, is not the basis upon which I'm going to conduct my operations.
You can if you want to, that's up to you.
Got to agree with Icarus and Agent - and I have run up against this in the past. The argument "well most pilots don't do that" or "there's never a TAF for there, so use the ARFOR", or something else that sounds similar, is not the basis upon which I'm going to conduct my operations.
You can if you want to, that's up to you.
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In response to the original question, just think of it as each temp/QNH being valid 90 mins either side of their forecast time (except for the first one because that is a spot forecast for the same time that the TAF commences, so you only move forward 90 mins from there). E.g. for a TAF commencing at 0600, the published QNH values are valid for spot times of 0600, 0900, 1200, 1500 (every 3 hours). You use whichever QNH that your arrival time falls within 90 mins of. E.g. ETA 1325 – you would use the 1200 QNH. Six minutes later and you would use the 1500 QNH. Hope that helps.
I don’t agree. It is not sensible and doesn’t make any logical sense. If an ARFOR was acceptable for determining alternate requirements, wouldn’t you just use that if the TAF wasn’t available or was provisional? So in the event that a certain TAF is provisional (cavok) and the corresponding ARFOR is fine, the aerodrome with the provisional forecast would need an alternate but a busted bush strip 3 nm away that is never issued with a TAF wouldn’t?
How could you tell if the crosswind at your destination was to exceed the maximum for your aircraft based on an ARFOR? How could you tell if any wx deteriorations were inter or tempo?
... unless cloud if forecast less than scattered below LSALT +500ft and vis greater than 8km.
Wrong! I know it says exactly those words in the AIP, but in the case of aerodromes that NEVER have TAFs issued for them, that is not what is meant.
Try again.
Try again.
How could you tell if the crosswind at your destination was to exceed the maximum for your aircraft based on an ARFOR? How could you tell if any wx deteriorations were inter or tempo?
If there's no TAF, there's probably no Navaids (eg station strip).
So more than likely, you'll need an alternate anyway!
So more than likely, you'll need an alternate anyway!
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Personally, I don't find it that hard to interpret. I think the entire TAF requires a certain level of knowledge to interpret correctly and the temp/QNH section is no different. Adding more QNHs and temps without actually increasing the precision of the forecast would seem counter intuitive to me. But hey, I just drive aeroplanes around 
Originally Posted by FDG135
Getting warmer!
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This one gets dragged out every now and then but never seems to get settled. Is anyone aware of this ever coming up in a CASA investigation or court case and having some sort of precedent set?
Originally Posted by Berner
Is anyone aware of this ever coming up in a CASA investigation or court case and having some sort of precedent set?
Bloggs it does go to the level of literacy amongst our ranks that some cannot make simple sense of "If an aerodrome forecast is not available..."
Judging by some of the poorly thought out, illogical arguments seen on this forum and the poor use of english grammar and spelling not surprising really.
On the TEM thread apparently it is all a waist(sic) of time.
Judging by some of the poorly thought out, illogical arguments seen on this forum and the poor use of english grammar and spelling not surprising really.
On the TEM thread apparently it is all a waist(sic) of time.
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Are you geniunely interested in people's opinions or is this just a test?
I have not yet found a pilot that understands the rule regarding TAFs.
Everybody seems to think that, unless you have a TAF for your destination, you must provide for an alternate. But this understanding is mostly wrong.
It is easy to see why everybody has this erroneous understanding. It is because of that poor wording in the AIP. Here is that wording:
AIP GEN 57.1.3 (page 88 of the PDF from the web)
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.
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.
That AIP wording only applies to aerodromes that NORMALLY have a TAF issued for them - and that includes aerodromes with "part time" TAFs.
It does NOT apply to aerodromes that NEVER have TAFs issued for them. This aspect is not well communicated in the AIP wording.
If the aerodrome NEVER has a TAF issued for it, you do NOT need to provide for an alternate (for the TAF reason - you may still need the alternate for other reasons, however. See below).
If the aerodrome NORMALLY has a TAF - including those with TAF coverage that is not round the clock - then the above AIP wording applies (i.e: yes, you must provide for an alternate if the TAF has not been issued, or has been marked "provisional").
To understand how and why this is the intent of the rule, it is necessary to look at ALL the rules relating to alternate requirements (especially those related to reasons of weather, but also those related to navaids).
I will come back to this thread later, but for now, will pose a question that may help to resolve this question instantly:
Regarding weather aspects, for non instrument approach aerodromes, the rules only require nomination of an alternate when the forecast cloud is more than SCT below the final route segment LSALT + 500'.
Application of this above rule, by day, will often mean that the provision of an alternate is NOT necessary. And, given that these are non instrument approach aerodromes, there usually won't be a TAF for them.
So, the question is:
If it is as simple as NO TAF = ALTERNATE REQUIRED, then why does the above rule exist?
Ignore all the above re RPT. I have never learned the rules re RPT, but believe they different to what I have quoted above.
Last edited by FGD135; 21st Mar 2011 at 03:18. Reason: Added the disclaimer re RPT
Originally Posted by FDG135
Off topic I know, but can somebody answer this:
If planning an IFR flight to a destination that does NOT have a TAF, is there a requirement to plan for an alternate (for the reason that there is no TAF)?
Assume that the destination in question is one of those that NEVER have TAFs issued for it (as opposed to those destinations that do have TAFs, but whose coverage is for less than 24 hours).
If planning an IFR flight to a destination that does NOT have a TAF, is there a requirement to plan for an alternate (for the reason that there is no TAF)?
Assume that the destination in question is one of those that NEVER have TAFs issued for it (as opposed to those destinations that do have TAFs, but whose coverage is for less than 24 hours).
Originally Posted by FDG135
Just a test. A test to ascertain how many pilots truly understand alternate aerodrome requirements.
Thread Starter
As the original poster of "this" thread, my question was not to explain how it worked, as this is very simple, but WHY it is like it is? muffman's first post is the only reply that seems to have anything to do with my question. In true PPRuNe thread drift fashion.....here we are. 
All good though, I love a good discussion/debate. Especially when we can all learn or rather relearn something that can add to safety.
anywho back to the banter
FGD135, what about the 8k's vis? seems your test has some flaws!!!
All good though, I love a good discussion/debate. Especially when we can all learn or rather relearn something that can add to safety.
anywho back to the banter
FGD135, what about the 8k's vis? seems your test has some flaws!!!
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FGD135.
You might quote ATC Flight planning 1.2.1:
“A forecast must be either a flight forecast or an area forecast with an aerodrome forecast for the destination and, when required, the alternate aerodrome. For a flight to a destination for which a prescribed instrument approach procedure does not exist, the minimum requirement is an Area Forecast”
No problem, so we can still depart without a TAF for our destination, but I don’t believe this absolves us of ATC Airports and Ground Aids 3.1.3 (Alternate Aerodromes) which clearly states that “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”. There is no getting around this one!
ATC Airports and Ground Aids 3.3.2 (a) “… a flight may be planned under IFR by day to a destination aerodrome which is not served by a radio navigation aid without the requirement to provide for a suitable alternate, provided that: a) not more than SCT cloud is forecast below the final route segment LSALT +500ft and forecast visibility at the destination aerodrome is not less than 8km…” How could you tell the forecast visibility at the destination aerodrome with only an Area Forecast? These alternate minima are based on a TAF as required by 3.1.3 above. The only reason they refer to the “final route segment” is to calculate an aerodrome alternate minima which should get you visual by your LSALT.
ATC Airports and Ground Aids 3.2.1 (d) also requires an alternate if the forecast crosswind or downwind component is more than the maximum for the aircraft (including gusts). How could you comply with this without a TAF?
In summary, you need a TAF for your destination. You are permitted to depart without a TAF if your destination is an aerodrome without an instrument approach procedure, or the normal TAF is not available or provisional, but you must carry fuel for a suitable alternate with a firm forecast.
You might quote ATC Flight planning 1.2.1:
“A forecast must be either a flight forecast or an area forecast with an aerodrome forecast for the destination and, when required, the alternate aerodrome. For a flight to a destination for which a prescribed instrument approach procedure does not exist, the minimum requirement is an Area Forecast”
No problem, so we can still depart without a TAF for our destination, but I don’t believe this absolves us of ATC Airports and Ground Aids 3.1.3 (Alternate Aerodromes) which clearly states that “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”. There is no getting around this one!
Regarding weather aspects, for non instrument approach aerodromes, the rules only require nomination of an alternate when the forecast cloud is more than SCT below the final route segment LSALT + 500'.
Application of this above rule, by day, will often mean that the provision of an alternate is NOT necessary. And, given that these are non instrument approach aerodromes, there usually won't be a TAF for them.
So, the question is:
If it is as simple as NO TAF = ALTERNATE REQUIRED, then why does the above rule exist?
Application of this above rule, by day, will often mean that the provision of an alternate is NOT necessary. And, given that these are non instrument approach aerodromes, there usually won't be a TAF for them.
So, the question is:
If it is as simple as NO TAF = ALTERNATE REQUIRED, then why does the above rule exist?
ATC Airports and Ground Aids 3.2.1 (d) also requires an alternate if the forecast crosswind or downwind component is more than the maximum for the aircraft (including gusts). How could you comply with this without a TAF?
In summary, you need a TAF for your destination. You are permitted to depart without a TAF if your destination is an aerodrome without an instrument approach procedure, or the normal TAF is not available or provisional, but you must carry fuel for a suitable alternate with a firm forecast.
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patienceboy,
As I said in an earlier post, that rule applies only to aerodromes that normally have TAFs issued for them. You are reading the wording way too literally. There is a subtlety in the wording that you are not picking up. Here is that wording again:
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.
Note the words "not available". Such wording is not the same as "does not exist". In everyday communication - written and oral, formal and informal - the expression "not available" implies that the particular thing is usually available.
If you went to the government and said to them "I would like to take up your offer of the free Ferrari now please", would they say "that is not available", or would they say "that does not exist"?
What would the implication be if their response was the former?
That expression - "not available" - is used in another meteorologically related place in the AIP. I quote that section here. Note how, in this case, the overall intent is much more clear (given our prior knowledge that Area Forecasts are valid for daytime periods only):
From AIP GEN 3.5:
10.3 Forecasts for Flights - Valid Area Forecasts not Available
10.3.1 Route forecasts required for flights for which valid Area Forecasts are not available will be supplied subject to the prior notification specified in the following table: ...
You said:
The area forecast will tell you if all, or part of the area, has visibility less than 10 km. The whole point of the area forecast is to warn you of things like this. Don't expect it to give you a list of individual visibilities at individual aerodromes.
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.
Here's another question for you. Take a look at AIP ENR 1.1-57.2.12. About IFR flights, it says:
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.
The question is:
Why does the directive only apply to aerodromes with an instrument approach? If your understanding is correct (i.e, NO TAF = ALTERNATE) then why is the instrument approach qualification in there?
Another way to consider the question of whether "NO TAF = ALTERNATE" is true or not is to look at the effects of such a rule and ask whether those effects could be intended by the regulatory authority.
That poorly worded passage in the AIP refers to both VFR and IFR flight.
Under your understanding, a VFR flight to a small destination 50 NM away (e.g farm strip), in the middle of the day, without a cloud in the sky, would have to provide for an alternate (because there is no TAF).
Does that sound like the kind of effect the regulator was looking for?
Under the correct interpretation of the rule, however, the VFR aircraft would only need the alternate if that flight was at night.
There is no getting around 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.
Note the words "not available". Such wording is not the same as "does not exist". In everyday communication - written and oral, formal and informal - the expression "not available" implies that the particular thing is usually available.
If you went to the government and said to them "I would like to take up your offer of the free Ferrari now please", would they say "that is not available", or would they say "that does not exist"?
What would the implication be if their response was the former?
That expression - "not available" - is used in another meteorologically related place in the AIP. I quote that section here. Note how, in this case, the overall intent is much more clear (given our prior knowledge that Area Forecasts are valid for daytime periods only):
From AIP GEN 3.5:
10.3 Forecasts for Flights - Valid Area Forecasts not Available
10.3.1 Route forecasts required for flights for which valid Area Forecasts are not available will be supplied subject to the prior notification specified in the following table: ...
You said:
How could you tell the forecast visibility at the destination aerodrome with only an Area Forecast?
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.
Here's another question for you. Take a look at AIP ENR 1.1-57.2.12. About IFR flights, it says:
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.
The question is:
Why does the directive only apply to aerodromes with an instrument approach? If your understanding is correct (i.e, NO TAF = ALTERNATE) then why is the instrument approach qualification in there?
Another way to consider the question of whether "NO TAF = ALTERNATE" is true or not is to look at the effects of such a rule and ask whether those effects could be intended by the regulatory authority.
That poorly worded passage in the AIP refers to both VFR and IFR flight.
Under your understanding, a VFR flight to a small destination 50 NM away (e.g farm strip), in the middle of the day, without a cloud in the sky, would have to provide for an alternate (because there is no TAF).
Does that sound like the kind of effect the regulator was looking for?
Under the correct interpretation of the rule, however, the VFR aircraft would only need the alternate if that flight was at night.
Last edited by FGD135; 23rd Mar 2011 at 14:49.
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FGD135
You have to read this in conjunction with (a) and in the knowledge that it is talking purely about meteorological alternate minima. It is basically saying that for aerodromes with an instrument approach you can use the published alternate minima, unless the forecast is unavailable or provisional (which is a redundant clause since we already knew that). The reason it refers to “instrument approach procedure” is because aerodromes without a procedure simply wouldn’t have a published alternate minima. I am not defending the way this is written in any way! See below.
I agree! 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.
No he wouldn’t. See below.
Section 16 lists the “locations for which TAFs are issued”
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?
I don’t agree that an area forecast can be used to calculate meteorological alternate minima. This is a major point. An ARFOR is a general forecast for a very large area to be used enroute. In addition to points already alluded to, ENR 57.2 (Alternate Aerodromes – Weather Conditions) continually refers to weather at the “destination”.
For example, I don’t agree that the area forecast gives you enough information to decide whether the crosswind or downwind will exceed the maximum for your aircraft. The wind at 3000ft very rarely resembles the wind on the ground with any degree of accuracy, and local winds can vary greatly due to terrain, proximity to coast etc. I have copied a random area forecast here:
This is great info enroute, but what is the wind forecast on the ground at our destination? 070/30? What about gusts? Smoke over land reduces visibility to 8km, but then this “may" be reduced further in thick smoke near fires. Where are these fires? Are they near my destination? Does this mean I need an alternate? Maybe I should just carry fuel to get somewhere with a firm aerodrome forecast. That makes sense.
Here's another question for you. Take a look at AIP ENR 1.1-57.2.12. About IFR flights, it says:
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.
The question is:
Why does the directive only apply to aerodromes with an instrument approach? If your understanding is correct (i.e, NO TAF = ALTERNATE) then why is the instrument approach qualification in there?
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.
The question is:
Why does the directive only apply to aerodromes with an instrument approach? If your understanding is correct (i.e, NO TAF = ALTERNATE) then why is the instrument approach qualification in there?
Another way to consider the question of whether "NO TAF = ALTERNATE" is true or not is to look at the effects of such a rule and ask whether those effects could be intended by the regulatory authority.
Under your understanding, a VFR flight to a small destination 50 NM away (e.g farm strip), in the middle of the day, without a cloud in the sky, would have to provide for an alternate (because there is no TAF).
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.
Note the words "not available". Such wording is not the same as "does not exist". In everyday communication - written and oral, formal and informal - the expression "not available" implies that the particular thing is usually available.
Note the words "not available". Such wording is not the same as "does not exist". In everyday communication - written and oral, formal and informal - the expression "not available" implies that the particular thing is usually available.
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?
The area forecast will tell you if all, or part of the area, has visibility less than 10 km. The whole point of the area forecast is to warn you of things like this. Don't expect it to give you a list of individual visibilities at individual aerodromes.
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.
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.
For example, I don’t agree that the area forecast gives you enough information to decide whether the crosswind or downwind will exceed the maximum for your aircraft. The wind at 3000ft very rarely resembles the wind on the ground with any degree of accuracy, and local winds can vary greatly due to terrain, proximity to coast etc. I have copied a random area forecast here:
This is great info enroute, but what is the wind forecast on the ground at our destination? 070/30? What about gusts? Smoke over land reduces visibility to 8km, but then this “may" be reduced further in thick smoke near fires. Where are these fires? Are they near my destination? Does this mean I need an alternate? Maybe I should just carry fuel to get somewhere with a firm aerodrome forecast. That makes sense.