circling
According to JAR OPS an ILS approach with a circle to land is a non precision approach.
The MDA for a circle to land is based upon 1.3Vs0, also the threshold speed. For CAT A: MDA Loc only (non precision) +200'.
Vs0 is the stall speed in landing configuration.
The maximum approach speeds and speeds for circling are: CAT A/90 B/120 c/140 D/165.
Countries are allowed to make adjustments in speeds and circling altitudes.
Every category aircraft has its own radius of the circle based upon the speed. Therefor the minima in visibility increases with increasing category (as you fly a further distance from the runway).
The larger MDA per CAT is based upon the loss of altitude during go-around and the increasing MOCA with distance from the airfield.
Los off sight of the runway due to clouds or visibility means go around.
This is funny because how are you going to execute a go around in a circle to land?
The rule is (i spend lot of time to find this out):
During approach a go around should be executed on the approach track. If you level of and start circling the go around should be executed on the intended landing track. (Opposite of the approach track so the first thing I would do is contact ATC)
Hope to have helped you!