Alternate required?

FlatPiglet

Filing Flight Plan
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FlatPiglet
So here's a TAF for a proposed destination:

FM261500 36005KT P6SM OVC050
PROB30 2616/2618 2SM -SN BR OVC020

Is an alternate required? The base forecast says no, but there's a 30% chance of less than 3 mile visibility. Does that 30% create the requirement for an alternate?

I know it's not a big deal to add one, and it's a good idea to have in mind..I'm asking purely from a regulatory POV, not an ADM POV.
 
My understanding is that the 30% probability of 2SM visibility means that you do have to file an alternate.
 
That's not answered in 14CFR91.

Gonna need a CC interpretation, and I didn't see one addressing that specifically in the first 5 pages I looked through.

I did however see a question of "can my destination be my alternate also? I think it can."

W. T. F.

BTW, the answer was no.
 
So here's a TAF for a proposed destination:

FM261500 36005KT P6SM OVC050
PROB30 2616/2618 2SM -SN BR OVC020

Is an alternate required? The base forecast says no, but there's a 30% chance of less than 3 mile visibility. Does that 30% create the requirement for an alternate?
Yes.
 
That's not answered in 14CFR91.
Sure it is.

Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima:​

A forecast saying there's a 30% probability it won't be is not a forecast saying it will be. As I recall from the olden times, this iis/was a question on the knowledge test.

The problem with alternate requirement is that they are often taught backwards — "we only need an alternate when..." — when the regulation actually tells us "we always need and alternate unless..."
 
Sure it is.

Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima:​

A forecast saying there's a 30% probability it won't be is not a forecast saying it will be. As I recall from the olden times, this iis/was a question on the knowledge test.

The problem with alternate requirement is that they are often taught backwards — "we only need an alternate when..." — when the regulation actually tells us "we always need and alternate unless..."

Also:

Paragraph (a)(2) of this section does not apply if : ... For aircraft other than helicopters. For at least 1 hour before and for 1 hour after the estimated time of arrival, the ceiling will be at least 2,000 feet above the airport elevation and the visibility will be at least 3 statute miles.​

Which also says "will be."

The OP's example TAF tells us, in effect, that there is a 70% chance that the visibility will be greater than 3SM, not that it "will be" greater than 3SM.
 
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Yep, PROB and TEMPO are count like they were sure things.
 
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Is there any reason you would not file an alternate for standard practice?

there could be a whole host of reasons why at the last minute you can't go to your originally planned destination.. might as well have a backup planned and briefed

Right??
 
Just file an alternate and don't worry about it if in doubt. It's not like you HAVE to go there.

And if you can't get into your destination you can go to an airport that is NOT your filed alternate.
 
Is there any reason you would not file an alternate for standard practice?
I guess it doesn't hurt to file an alternate even if one is not required, but you still need to know whether the alternate is required or not, because that determines whether your fuel planning must account for flying from your destination to your alternate, and that can affect whether you're going to have to make a fuel stop or not.
 
I guess it doesn't hurt to file an alternate even if one is not required, but you still need to know whether the alternate is required or not, because that determines whether your fuel planning must account for flying from your destination to your alternate, and that can affect whether you're going to have to make a fuel stop or not.
Not if you assume you need the fuel and plan accordingly.
 
I guess it doesn't hurt to file an alternate even if one is not required, but you still need to know whether the alternate is required or not, because that determines whether your fuel planning must account for flying from your destination to your alternate, and that can affect whether you're going to have to make a fuel stop or not.
Personally speaking as I slowly get older I find my flying style has shifted towards the more careful side. There's nothing wrong with having an alternate on a clear VFR day and enough fuel to get there. You never totally know what might happen. Maybe you're going somewhere with a single runway and a plane gets disabled there? Now what? Rather than scramble it's easy to just automatically switch to option 2

But I agree, one should still know the rules

For what's it's worth, in the case of the OP, to me a "30% chance" of it being below the requirement means I need an alternate as I cannot definitely say that it WILL be within the required limits
 
I have to say, I've never seen PROB in a TAF.
 
I have to say, I've never seen PROB in a TAF.
JFK TAF today. It’s definitely not uncommon.

M8TDNxC.jpg
 
I fly into fields with no approaches, so I file alternates all the time anyhow.
 
Sure it is.

Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima:​

A forecast saying there's a 30% probability it won't be is not a forecast saying it will be. As I recall from the olden times, this iis/was a question on the knowledge test.

The problem with alternate requirement is that they are often taught backwards — "we only need an alternate when..." — when the regulation actually tells us "we always need and alternate unless..."

But that's for the alternate. The OP showed the weather for the destination. That quoted reg doesn't apply.
 
But that's for the alternate. The OP showed the weather for the destination. That quoted reg doesn't apply.
The destination is covered by:

(2) Appropriate weather reports or weather forecasts, or a combination of them, indicate the following:

(i) For aircraft other than helicopters. For at least 1 hour before and for 1 hour after the estimated time of arrival, the ceiling will be at least 2,000 feet above the airport elevation and the visibility will be at least 3 statute miles.


So it's even broader there. IF anytime during the two hour window around the ETA, it could possibly or temporarily be worse, then you need the alternate. As I said, PROB or TEMPO as as good as the sure thng.

Where's the source for that?
If there's a probability or temporarily lower the two hours, it's no longer the case that the ceiling and visibility will be above the limits mentioned. While I don't think you will find a hard reference for GA, the sense of the FAA's application of these conditional blocks to things like Part 121 supports this interpretation.
 
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But that's for the alternate. The OP showed the weather for the destination. That quoted reg doesn't apply.
Oops. Bad copy/paste. How about (b)(2)? Same "will be" language for when you don't need a filed alternate.

(b)(2) Appropriate weather reports or weather forecasts, or a combination of them, indicate the following:
(i) For aircraft other than helicopters. For at least 1 hour before and for 1 hour after the estimated time of arrival, the ceiling will be at least 2,000 feet above the airport elevation and the visibility will be at least 3 statute miles.​
Probability it "won't be" is still not "will be."
 
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Out here in the west we just filed Lewiston Idaho as an alternate. It is always (never use that word) a good choice.
 
....There's nothing wrong with having an alternate on a clear VFR day and enough fuel to get there. You never totally know what might happen. Maybe you're going somewhere with a single runway and a plane gets disabled there? Now what? Rather than scramble it's easy to just automatically switch to option 2.....

Cancel IFR and go wherever the F you want? I would think as part of GOOD pre flight planning you’ve considered alternates whether you filed one or not. But yeah, doesn’t hurt to actually file it.
 
Oops. Bad copy/paste. How about (b)(2)? Same "will be" language fis when you dint need a filed alternate.

(b)(2) Appropriate weather reports or weather forecasts, or a combination of them, indicate the following:
(i) For aircraft other than helicopters. For at least 1 hour before and for 1 hour after the estimated time of arrival, the ceiling will be at least 2,000 feet above the airport elevation and the visibility will be at least 3 statute miles.​
Probability it "won't be" is still not "will be."

But we all know forecasts aren't 100% either. They aren't a will be, just better than 70% chance of will be. Just like as I look outside today. This forecast was wrong. Every forecast is a probability, and not a guarantee. The regulation you quoted said "will be" as in guaranteed. Iron clad. 0 chance of it not being. But that's never the case. So where's the regulation that says 70% probability is unacceptable but an unlisted probability is acceptable? That's all I'm asking.

All this said, I'd file alternate, but the question wasn't "would you."
 
But we all know forecasts aren't 100% either. They aren't a will be, just better than 70% chance of will be. Just like as I look outside today. This forecast was wrong. Every forecast is a probability, and not a guarantee. The regulation you quoted said "will be" as in guaranteed. Iron clad. 0 chance of it not being. But that's never the case. So where's the regulation that says 70% probability is unacceptable but an unlisted probability is acceptable? That's all I'm asking.

All this said, I'd file alternate, but the question wasn't "would you."
The reg says weather reports/forecasts indicate that the weather “will be”, not the weather “will be”.

Reports and forecasts can be wrong, but the reg says they’re what you need to use.
 
The reg says weather reports/forecasts indicate that the weather “will be”, not the weather “will be”.

Reports and forecasts can be wrong, but the reg says they’re what you need to use.

So, if it can be demonstrated that over a given time period the forecasts for a certain area are historically wrong a given percentage of the time, say 40% of the time, are we now required to file an alternate because history indicates that forecasts only have a 60% accuracy? I mean, I am using "all available information" for that flight, am I not?

If we want to let the regs be open for interpretation, then let's open them up for interpretation.
 
So, if it can be demonstrated that over a given time period the forecasts for a certain area are historically wrong a given percentage of the time, say 40% of the time, are we now required to file an alternate because history indicates that forecasts only have a 60% accuracy? I mean, I am using "all available information" for that flight, am I not?

If we want to let the regs be open for interpretation, then let's open them up for interpretation.
The reg doesn’t provide a means to determine the statistical accuracy of the forecast, nor do I believe an advisory circular exists on the subject. If the forecast is wrong, hopefully the reports will reflect that, and you can make your determination legally. If both are wrong, you might plan and file an alternate that you don’t need, don’t plan and file an alternate that you don’t need, or don’t plan and file an alternate that you do need.

in any case, you keep up with the weather enroute, and divert if necessary.

Why open them for interpretation when reading them works?
 
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Related question: Now that textual area forecasts are gone, is it permissible to use the graphic forecast if your destination or alternate do not have a TAF?
 
Related question: Now that textual area forecasts are gone, is it permissible to use the graphic forecast if your destination or alternate do not have a TAF?
Yes. Again its in the plain English words of the regulation: "Appropriate weather reports or weather forecasts, or a combination of them, indicate the following..." It doesn't say "A textual area forecast or TAF indicates the following..."

I'm sure someone can play around with what are considered "appropriate" reports and forecasts, but it's basically a recognition that technology changes and some things just aren't' conducive to super detailed regulation.
 
So, if it can be demonstrated that over a given time period the forecasts for a certain area are historically wrong a given percentage of the time, say 40% of the time, are we now required to file an alternate because history indicates that forecasts only have a 60% accuracy? I mean, I am using "all available information" for that flight, am I not?

If we want to let the regs be open for interpretation, then let's open them up for interpretation.
Taking the reg literally, it says that the alternate requirement is to be based on what the forecasts "indicate," which in the OP's example is that there is only a 70% chance of the visibility being better than 3SM. The purpose of the requirement to file and carry fuel for an alternate is to protect ourselves from the consequences of the known inaccuracy of forecasts. Treating a 70% chance as equivalent to "will be" and therefore sufficient to avoid the alternate requirement would defeat that purpose.

On the other hand, using the known inaccuracy of forecasts as a requirement to ALWAYS file an alternate would render 91.169(b)(2) meaningless. My understanding is that courts tend to reject interpretations that render the regulation being interpreted meaningless.
 
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Yes, but ambiguous regulations are usually left to the interpretation of the agency.
My understanding is that ALL regulations are left to the interpretation of the agency. :(
 
The fact that forecasts aren't accurate is why the alternate require is pretty broad: 2 hours, 2000-3. If they were dead on accurate, the alternate would only be required if the weather at the destination was close to the minima for the approach.
 
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