According to the CAA, visual line of site is considered to be 500m max horizontal distance & 400ft max altitude AGL.

I understand & agree with the horixontal distance as far as VLOS is concerned, but the 400ft altitude surely has litttle to do with visibility & is there purely to avoid other aircraft? which is fine.

What then, would be the maximum distance downwards, below the pilot if flying from an elevated platform, a mountain summit for example?

My logic would suggest I'd be safe to fly within a cylinder with a 500m radius, with a height limit of 120m (400ft) & either a overall depth of 620m (500m + 120m) or at worst, within a sphere below ground level of radius 500m.

Any takers?

PaulKerry Posted at 2016-1-29 00:24
Whilst you and I are both aware that 500m horizontal distance with no altitude difference and 500m h ...

That's exactly how I see it & was the answer I was looking for.  A common sense approach.  As long as I can see the drone & judge it's relative distance from nearby objects, including things like power lines, I should be ok within 500m distance in any direction other than up (where you would start hitting planes & stuff).