Originally Posted by
mmm345
Whilst this is quite a confusing topic ( from what i can see this isnt the first thread of the topic and head is starting to hurt alot), the AIP states multiple points to suggest that for a non IAP destination with no TAF, no alternate AD is required if GAF shows can maintain LSALT+500ft and 8km on final route segment.
Namely, ENR 1.1-92 refers to the clause about " Where the TAF is unavailable" ( potentially using language that implies that this clause refers to destinations where a TAF is normally available"- begins with " For AD with an IAP", the question of this thread is in regard to a negative IAP aerodrome.
Clause C of ENR 1.1-92 refers to the question of this thread, for " AD without an IAP".
Additionally, in ENR 1.10, it states that when an IAP does not exist at an AD- the minimum forecast required is a GAF, why would they say this if you need an alternate if you dont have a TAF.
The unavialbility of a normally published TAF is only a factor at an aerodrome with a published IAL. The TAF would be used in the planning phase to align with the alternate minima on the chart and thus determine alternate requirements.
At a non IAL chart destination, there is no published alternate minima on the chart to match the weather on the TAF with. Thus, the AIP states that you must conisder the LSALt on the final route segment , add 500ft and enter with a visbility of 8km. Consult the GAF ( as the TAF is null and void outside of 5nm ARP) and determine alternate requirements from this. The TAF for such a destination without an IAP would be useless ( although handy for SA) for planning alternates as 99% of the time the final route segment will not be within 5nm of the destination and thus requires consult of the GAF anyway.
Agree completely with mmm345. As stated by someone else it does not apply at night for >5700.
Also, I always have a peek at the GAF when considering fuel loads even when there is a TAF as GAFs by definition are way more conservative. Criteria for inclusion of phenomena on the TAF is minimum 30% probability vs 10% on the GAF, and is not restricted to the 5nm fishbowl surrounding the aerodrome. It's very common to see TS on the GAF for the area around Darwin, but not on the TAF or TTF. The storms on these days sometimes ignore the Berrimah line.