Well, you need to be able to do primary school arithmetic, there are lots of tedious conversions between litres, US gallons, pounds etc, but beyond that:
(1) You need a basic understanding of what a vector is, how to add vectors, how to resolve vectors into components in various directions. This is used in understanding the forces on an aircraft in flight, and in planning navigation taking the wind into account.
(2) A very basic understanding of trigonometry is also useful, mostly in relation to the above. When ATC tells you the wind speed and direction as you approach to land, for example, you need to be able to work out, in your head, how much of that is the crosswind component and whether or not you are going to attempt to land with that much crosswind. *But*, nobody *actually* does this by memorising sine and cosine tables, they actually do it by memorising some very simple approximate rule of thumb, and this is entirely possible to do without actually understanding the trigonometry at all.
Altogether you're looking at enough maths to have occupied three or four lessons early on in the O-level course.