TAF Valid Period Clarification

[121Dispatch]

A TAF is issued 4 times a day (scheduled, I'm not talking about AMD/COR/RTD in this scenario).

When a TAF is issued at 2335z for instance, it's valid for 24 hours (valid from 00 to 00). Then another TAF is issued around 0535z (valid from 06 to 06).

Any thoughts on what happens to the 2335z TAF once the new one is issued? Is it still valid? I can't receive the 0535 TAF with worse weather (requiring an alternate for instance), and disregard it by saying, well, the 2335 TAF is better, so I'm going to use that since my flight is within the 24 hour period (I'm talking legality hear, not the smart decision).

I've always been under the impression that a TAF is valid for 24 hours, OR UNTIL SUPERCEDED, but I can't find any wording anywhere that states those words (although I've heard people say this).

Perhaps the reason this wording doesn't exist is so that if you are enroute and a new TAF is issued, you still have a "valid TAF" in your posession. Although, you DEPARTED with a current and valid TAF, so that really shouldn't be an issue, and a pilot should be keeping up with weather updates through FSS/Flight Watch.

Anways, whad'ya think? Superceded TAF still legal, or any source for wording otherwise?

 

[Richard]

Issued...Valid....

The one is expired when the other becomes Valid.

(EX: the 0600 is issued at 0535 but becomes valid at 0600. The previous TAF expires at 0600.)

I suppose it is not legal to use an issued TAF until it becomes valid.

 

[poadeleted20]

In addition to not using any TAF that has been superseded by a later issuance (either the new regular 6-hour cycle or an amended one with "AMD" on the line), note that the TAF is not always valid for 24 hours. I often see TAFs valid for a shorter period, usually 18 hours or so. Keep an eye on the valid time following the issue time:

"TAF KSBY 212325Z 222418 ..."

The underlined portion means that the TAF was issued at 212325Z (2325Z on the 21st) and the bold portion means it's valid from 24Z on the 21st until the next 18Z (in this case, 18Z on the 22nd). Usually you'll see 212400 (i.e., a full 24 hours), but not always.

As for changes in the TAF once you file your IFR flight plan, there's no legal requirement to reconsider your filed alternate requirements, but one should always do one's best to stay up with changes in the weather (actual and forecast) so a good alternative plan of action is always ready.

 

[121Dispatch]

Yep that's the same interpretation I held as well. I just overheard an instructor telling a student that a TAF was valid for 24 hours, and I added or until superceded. The response I got was "no - 24 hours" (again other than AMD/shorter period in valid time), and then I was asked for a reference that stated until superceded.

I couldn't find specific wording (or until superceded), but in all my years dispatching, knew we sure didn't use any old TAF's once the new ones came out.

Anyways, thanks for letting me know I'm not crazy (at least in this regard).

 

[poadeleted20]

Yep that's the same interpretation I held as well. I just overheard an instructor telling a student that a TAF was valid for 24 hours, and I added or until superceded. The response I got was "no - 24 hours" (again other than AMD/shorter period in valid time), and then I was asked for a reference that stated until superceded.

I couldn't find specific wording (or until superceded), but in all my years dispatching, knew we sure didn't use any old TAF's once the new ones came out.

I cannot find any NTSB case or FAA Counsel interpretation on point, but I simply cannot imagine either the FAA or the NTSB accepting a pilot's use of an earlier forecast for IFR flight planning when a newer one is available at the time of the planning as being compliant with 14 CFR 91.103, especially if the later forecast is worse and changes the fuel/alternate planning (really, the only time TAF's are a legal issue). If nothing else, it suggest really bad judgement even if it doesn't constitute a technical violation of the rules.

 

[midlifeflyer]

I cannot find any NTSB case or FAA Counsel interpretation on point, but I simply cannot imagine either the FAA or the NTSB accepting a pilot's use of an earlier forecast for IFR flight planning when a newer one is available at the time of the planning as being compliant

I agree. "Well the old one was still valid" sounds like a jailhouse lawyer type of technicality (like the ones folks always come up with to try to fit a commercial op into Par 91) that usually doesn't hold up in the real world.