The TTF that is issued at 0900 replaces the TAF until 1200 [three hours]. Anyone arriving between 0900 and 1200 must plan according to that TTF and ignore the TAF. However when the next TTF comes out at 1000, it overrides the first TTF and remains valid until 1300. All arrivals between 1000 and 1300 must now plan according to the most recent TTF. Arrivals after 1300 refer to the TAF for flight planning purposes.

Thank you, Bob. I've understood your reply and thought I'd give it a go with a Canberra TAF,TTF from today. Can you let me know if my decode is correct.

CANBERRA (YSCB)
TAF YSCB 291712Z 2918/3018
14005KT 9999 BKN015
BECMG 2921/2923 05008KT 9999 SCT030
BECMG 3001/3003 34010KT 9999 FEW045
FM300800 05008KT 9999 FEW035
BECMG 3015/3017 08005KT 9999 BKN018
RMK
T 15 17 21 26 Q 1012 1015 1015 1013

TTF METAR YSCB 292300Z 05009KT 9999 FEW025 SCT035 21/12 Q1015
RMK RF00.0/000.0
NOSIG

For aircraft arriving between 2300Z on 29th and 0200Z on 30th, the TTF is valid, the TAF can be ignored and no signifigant change in the TTF is expected for the 3 hours validity of the TTF.

If the aircraft arrival time is 0230Z on 30th, the TAF is valid and can expect visibility of 9999 and FEW045?

Thank you once again.

Yep. You've got it. Also the next TTF will be out at 2400, and it will replace the current TTF and the TAF for the next three hours i.e. until 0300

Looks like you have the gist of it. Important to note with the TTF the NOSIG means no significant change from the observed conditions in the METAR (or SPECI) over the next 3 hours.

The other thing to note is that the vast majority of sites where a TTF is issued will actually issue them half-hourly these days, as most sites issue half-hourly METARS. They may even be issued more frequently if a non-routine SPECI observation is issued because conditions have deteriorated below minima in between half-hourly reports.

Just to complicate things further, not all TTF sites are staffed 24 hours, and this means that there may be periods (usually overnight) where AUTO METAR and SPECI observations continue to be issued, but without the attached TTF. The TTF's for the last 3 hours prior to them no longer being issued will tell you to use the TAF after the non-issue time.

Great. Thanks Bob. 🙂

You might also find the knowledge centre at BoM to be useful. They have information sheets on the different Aviation weather services (including TTFs) as well as fact sheets on various hazards as well as meteorology references such as a glossary and a list of abbreviations:

[url= http://www.bom.gov.au/aviation/knowledge-centre/products-hazards/#Weather+Advice+for+Your+Safety/ ]http://www.bom.gov.au/aviation/knowledge-centre/products-hazards/#Weather+Advice+for+Your+Safety/[/url]

It is a great resource for pilots.

Cheers,

Rich

Thank you. I have one more question. This is relating to Q7 from page 7.30 of the book.

TAF YBBN 242215Z 2400/2506 16015KT 9999 -RASH SCT025 SCT040
T17 18 19 19 Q1020 1018 1017 1017

METAR/TTF YBBN 0300Z 18020 9999 -RASH BKN020 18/16 Q1017
RMK RF00.0/000.0 NOSIG

Q: The lowest cloud base forecast for an arrival at YBBN at 0700 is
A: 2000 ft AGL
B: 2500 ft AGL

How do I work out the weather for arrival at 0700 when the TTF and the TAF both end at 0600? Just a little confused with this one. Have I missed something? Sorry if this is a silly thing to ask.

Thank you again.

Hi sydpilot,,

The answer is (b). The TAF is valid from 2400 to 2506 so an arrival at 0700 must be referring to 0700 on the 24th since there is no TAF for 0700 on the 25th, The TTF issue time is ambiguous and is actually an errata (thanks for bringing it to our attention!). TTFs, METARs and SPECIs represent their issue times as a 6-figure date-time group (AIP GEN 3.5 12.3.1)

For this question it doesn't matter anyway since the TTF would have expired whether the TTF was issued on the 24th or the 25th.

For an arrival at 0700, you would need to use the TAF which forecasts SCT at 2500ft.

Cheers,

Rich

Hi Richard,

As you rightfully say, the TTF expires at 0600 so we need to refer back to the TAF. In this instance though, the TAF also expires at 0600.

So do I just assume that the cloud base for arrival at 0700 (an hour after the TAF expired) will still be 2500 ft?

Thanks,

Frederik

Hi Frederik,

The TAF has not expired though. It is valid from midnight of the 23rd/24th until 0600 on the 25th - in other words this is a 30 hour TAF. The flight arrival time must be at 0700 on the 24th since there is no TAF in the question for 0700 on the 25th.

You would never make assumptions about forecasts in real life or in the exam. CASA doesn't like that very much 😉

Cheers,

Rich

But of course, that makes perfect sense. It is a 30 hour TAF indeed.

Read the question, read the question, is what I've been told many a time.

Thank you again.