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Holding until weather improves (TAF3)

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baddles created the topic: Holding until weather improves (TAF3)

Hi all,
suppose we have a TAF3 forecast with validity 0900/0918 which forecasts very bad weather at the start of the forecast period, changing to very good weather at 0100 (FM 0100), and our ETA is 0050 Z.

So we're forecast to arrive into bad weather, which will be replaced by fine weather only 10 minutes afterwards, during the first 3 hours of the TAF3.

My interpretation of the rules is that:
  • for our ETA of 0050Z, we require either an alternate, or 40 minutes holding.
  • if instead our ETA is 0100Z (only 10 minutes later), we would not require an alternate, and would not require any holding fuel at all.

With ETA 0050Z we are inside a forecast period of bad weather, which surely triggers an OPR.
Then AIP ENR 1.1 para 10.7.2.3 states that, if weather is forecast to improve above the minima, then instead of an alternate, we can hold until the forecast time when weather improves, plus 30 minutes. That's 40 minutes.

With ETA 0100Z we are inside a forecast period of good weather, and since it is within the first 3 hours of the TAF3, there is no OPR for this arrival time. (ENR 1.1 para 10.7.2.9 says we do not have to apply buffers of 30 minutes described in paragraphs 10.7.2.7 and 10.7.2.9). There is no OPR, so there is no requirement for alternate or holding.

This seems perverse. The requirements for holding fuel change abruptly. Wouldn't it be more logical to allow the pilot arriving at 0050Z to hold for only 10 minutes, until the forecast time of change? But 10.7.2.8 does not apply to this situation. Am I misinterpreting the rules?

If the forecast was an ordinary TAF rather than a TAF3, then for ETA 0050Z we could hold for 40 minutes, and for ETA 0100Z we could hold for 30 minutes, and the requirements would not change abruptly over time.

Help!!
#1

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bobtait replied the topic: Holding until weather improves (TAF3)

You are never going to be faced with the choice between a TAF3 and a regular TAF. If a TAF3 is issued, there will be no TAF. The TAF3 is issued at selected airports only (mostly international plus some busy regional and military). The TAF3 is compiled by a 'team' of meteorologists with access to very reliable data from multiple sources including RADAR. and satellite observations. Along with the frequency of issue, this provides a very high degree of integrity that allows the requirement for 30 minute buffers to be lifted during the first 3 hours of validity. A normal TAF has nothing like that degree of integrity so it is necessary to introduce some 'wriggle room' for the commencement and completion of changes and/or variations.
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baddles replied the topic: Holding until weather improves (TAF3)

Thank you, Bob.

Unfortunately I'm still unclear.

My question is basically:

Is the 30-minute holding period mentioned in ENR 1.1 para 10.7.2.3
still applicable during the first 3 hours of a TAF3?

ENR 1.1 para 10.7.2.3 allows the pilot to hold until the forecast time when weather improves, plus 30 minutes.
The 30 minutes appears to be required in all circumstances, even in the first 3 hours of a TAF3.
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bobtait replied the topic: Holding until weather improves (TAF3)

The OPR for INTER (30 min) and TEMPO (60min) still applies for a TAF3, even during the first 3 hours. It's only the buffers that you can ignore.
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baddles replied the topic: Holding until weather improves (TAF3)

Thanks again Bob.

My question is about holding until the weather is forecast to improve at a specific time (FM) when that time is within the first 3 hours of a TAF3.

I think I've found an answer in the Part 91 MOS, section 8.04, which has rules that look very similar to the rules in ENR 1.1 para 10.7, but are subtly different.

Part 91 MOS section 8.04 subsection (5) says that the pilot can hold until the time at which the weather is forecast to improve (if that time is in the first 3 hours of a TAF3). So in my example, the pilot arriving at 0050Z would only have to hold for 10 minutes.

This is not the same as ENR 1.1 para 10.7.2.3 which implies that the pilot is obliged to hold until 30 minutes after this time. As far as I can see, none of the other statements in ENR 1.1 para 10.7 allow this rule to be modified to remove the 30 minutes during a TAF3.

So there appears to be a small contradiction between AIP and Part 91 MOS.
I guess the Part 91 MOS takes precedence..
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bobtait replied the topic: Holding until weather improves (TAF3)

I suppose that, for a TTF, it could be argued that if you arrived during the first 3 hours of validity the OPR would not include the 30 minute buffers. I can certainly appreciate your point though. Good question.
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