Supposing you have a TAF3, arriving in Sydney. The TAF3 is from 220730Z and the conditions are fine to land ( no alt or holding required )
Then FM220900 the conditions change to 26006KT 9999 thunderstorms FEW015 BKN018CB
Your ETA is 0850Z
The question asked how much holding/alternate requirements are needed if the following is forecast at Sydney.
My thoughts that as long as you arrive before the FM, then no alternate or holding is required? Is this correct?
Assuming that if you were to land at 0900, then the conditions require that an alternate is required is that correct?
I understand that in the first 3 hours of TAF3, the time buffers do not apply, but will apply 30 minutes before and after if it is after the first 3 hours
I also understand, that in a TAF3, from ENR1.1 10.7.2.9 that only any reduction in visibility or if there was a PROB30 or PROB40 for TS or associated severe turbulence, then you can ignore this? But if there were other deteriorations ie. if the CLOUD was > SCT below 1500 at ETA, or if the wind was > aircraft could handle? or if there was a definate TS at arrival, then holding fuel would be required? Is this correct?
Is there any reason why CASA has included only 2 parameters to ignore and not the others
Kind regards
Ravi
Hi Ravi,
Your thinking is broadly correct, but there is one important point in this example.
The TAF3 was issued/valid from 220730Z, so the first 3 hours are 0730Z to 1030Z.
Because the FM group is:
FM220900 26006KT 9999 TS FEW015 BKN018CB
and your ETA is 0850Z, you are arriving before the FM change begins.
Normally, an FM that creates an alternate requirement becomes effective 30 minutes before the FM time. However, at a TAF3 aerodrome, during the first 3 hours of the TAF3 validity, the 30-minute buffer does not apply. AIP ENR 1.1 para 10.7.2.9 says that at TAF3 aerodromes, during the first 3 hours of the TAF3 validity, the 30-minute buffers in 10.7.2.7 and 10.7.2.8 do not apply.
So for an ETA of 0850Z, you are before the FM220900 deterioration. On that basis, the FM weather would not require holding or an alternate for that ETA, assuming the weather before 0900Z is above alternate minima.
If your ETA was 0900Z or later, then the FM conditions apply. In this case the forecast includes TS and BKN018CB. A thunderstorm at the destination is one of the conditions that requires provision for a suitable alternate aerodrome. AIP ENR 1.1 para 10.7.2.1 includes “a thunderstorm or associated severe turbulence, or a forecast of at least a 30% probability of such an event” as an alternate trigger.
The cloud may also be relevant depending on the applicable alternate minima. For VFR aeroplanes, the alternate minima are a ceiling of 1500 ft and visibility 8 km. For IFR, it depends on the published alternate minima for the approach available to the pilot. But in your example, you do not need to rely on the cloud argument because the definite TS is enough by itself.
The TAF3 “ignore” provision is narrower than many students first think. During the first 3 hours of a TAF3, you may ignore:
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the normal 30-minute buffers, and
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the alternate/holding requirement arising from:
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probability of reduced visibility under 10.7.2.1(c), or
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PROB30/PROB40 for TS or associated severe turbulence.
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That does not mean you can ignore all bad weather in the first 3 hours. If the TAF3 is forecasting a definite thunderstorm, or definite cloud/wind below requirements, then those conditions still count. The special TAF3 relief mainly deals with the timing buffers and certain probability-based forecasts.
So the simple exam logic is:
ETA 0850Z: before FM220900, within the first 3 hours of the TAF3, so no 30-minute buffer. No alternate/holding required from that FM group.
ETA 0900Z or later: FM conditions apply. Definite TS is forecast, so an alternate is required unless the question gives you a valid holding-fuel option to wait until a specified improvement time.
Why did CASA only exclude those two probability/visibility cases? The practical reason is that TAF3 replaced the old TTF-style planning logic at major aerodromes. It is under close weather watch and is amended more responsively, so CASA gives some relief from buffers and certain probability-based triggers. But definite operationally significant weather, such as an actual forecast TS, low cloud, poor visibility or excessive wind, still has to be treated as real forecast weather.