Originally Posted by NorthSouth
I'd welcome anyone's views on what proportion of cloud cover (oktas) at or close to the MDH would give you a reasonable chance of acquiring visual reference and making a successful landing.
Three points for your model:
1) There are likely to be substantial non-linearities. The probability of getting in with 2/8 below MDA is likely to be greater than 3/4, because that cloud can be avoided by limited manoeuvring. Conversely, I don't think the chances of getting in with 7/8 of obscuring cloud are as good as 1/8, as the chance of blundering into it at some point and having to go around is much higher.
2) The lights may play a significant part. Without lights, cloud in pretty much fully obscuring. With full approach lights, you may well see the runway environment through 200 ft of cloud below.
3) CANPA vs dive & drive plays a part. The timescale for the instrument visual transition is shorter for CANPA, so I would imagine there's a higher probability of partial cloud obscuring the view at the critical time.
But no rules of thumb, I'm afraid, which is what you're really after.