The supplied answer to an exam question: When the visibility in a forecast is described as being above the alternate minimum of 8km, but the forecast is endorsed with a percentage probability of the visibility dropping to below 8km, an alternate is required during the validity of that period.

AIP ENR 1.1 para 10.7.2.1(c).
The correct answer is: 10 percent probability of haze reducing visibility to 4 km


AIP ENR 1.1 para 10.7.2.1(c) says it needs to be {at least 30% probability} not just any percentage probability.

So how can 10% be valid?

It would be better if you posted the whole question.

Regardless, at the exam you will have to eliminate and pick the best available answer.

When they say "at least", that means any number between 30 and 99.

The question asked out of four options what would force the requirement for an alternate. I selected a 20kt crosswind on the only available runway. The other two options were:


a visibility of 8 km
six octas of cloud with a base of 1500 ft AGL

both of which are acceptable. Given a 20kt crosswind is a lot for GA, and 10% prob falls bellow the minimum 30%, I dont see how the supplied answer can be the correct one.