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## TAF question- Alternate requirements

• SteveS
• Topic Author

### SteveS created the topic: TAF question- Alternate requirements

Hi all,

Could anyone please shed some light as to why these conditions are below the alternate minima? As I understood it, cloud more than 4/8ths and visibility below alternate minima. As stated in the TAF, there is cloud below the alternate minima but none more than 4/8ths. Should the answer for this question be A instead of C?

• Posts: 138

### Bosi72 replied the topic: TAF question- Alternate requirements

The answer is in ENR 1.1 10.7.2.3, but also read whole 10.7.2 paragraph.

As you know, the weather doesn't change instantaneously at exact minute. It is assumed it takes 30mins to change.

When the forecast changes from bad to good weather, you have to take away 30min from the >good< weather to ensure conditions will be good.

When the forecast changes from good to bad weather, you also have to take away 30mins from >good< weather to ensure the weather will be good.

So, always take away 30mins from the good weather.

Also FEW+SCT=BKN

Hope above helps
The following user(s) said Thank You: SteveS

• Posts: 2447

### bobtait replied the topic: TAF question- Alternate requirements

The aternate minima for this aerodrome is 1200ft. The SCT cloud is at 1000ft and the FEW cloud is at 800ft. Since SCT is 3/8 to 4/8, and FEW is 1/8 to 2/8, the total could be as much as 6/8 at different levels below the alternate minima. If FEW and SCT exist below the alternate minima, you must consider the cumulative effect. See AIP ENR 1.1 para 10.7.2.1 (a).

Bob
The following user(s) said Thank You: SteveS