Let me throw in a scenario.
You are landing on a runway which starts right on a coast, and the land (but not the sea) is covered in a layer of cloud.
So you descended, straight-in of course, all the way to short final, in CAVOK conditions.
Due to wind, you need to circle to the opposite runway.
Horizontal vis is great. No obstacles.
Assume this was a VFR flight i.e. the circling minima on the Jepp plate are not applicable.
How low can that cloud be, before the circling is illegal?
If there is a published circling procedure it will be stated. If there is none, I would say that there is no illegal circling altitude. The SERA is pretty clear that you can descend below 500 ft for landing. What is suitable is another question however.
Peter wrote:
How low can that cloud be, before the circling is illegal?
I would say 500ft unless you can be on the ground at the numbers of the cross runway without losing VMC 
But then in licenced aerodromes minima you will find something along “no VFR under 600ft”?
I don’t believe one can dodge cloud-base for landings but not for takeoffs at least when controlled (I recall waiting at LeTouquet for an SVFR departure just after morning fog liftoff, it did looks flyable at sea side of the runway but not at 31 numbers)
Peter wrote:
Due to wind, you need to circle to the opposite runway.
Not a hypothetical as one may think, try asking ATC to land at Redhill cross-runway that sits in Gatwick zone when cloud base is 1000ft, I recall the reply was a clear NO that runway is not available…
I recall waiting at LeTouquet for an SVFR departure
Do not confuse an airport in CAS. These have a min cloudbase requirement.
Peter wrote:
Do not confuse an airport in CAS. These have a min cloudbase requirement.
Yes, measured cloud-base was 400ft, you need 600ft for SVFR, tough at end of runway it was CAVOK ATC did not yet issue SVFR departures until the whole lot clears up, so I doubt the ability to see the runway/sky is all you need to “remain VMC” OCAS…
I have had instructors request me to demonstrate circle to land at 350ft due to both the absolute requirement to not go IMC again and to ensure that I could correctly handle the aircraft in this situation and not be intimidated by being so close to the ground.
I both enjoyed it and happily agree it’s essential not to go IMC at 500ft under pressure in a turn.
At this point you’re having a bad day and that’s definitely when remaining visual and under control will save the day.
I once (many moons ago) callled Biggin, Shoreham, Redhill Bembridge and Headcorn for a weather report. The TAFs from some Southern airfields had some prob 20’s
They all declared suitable weather. My destination was Bembridge.
At the south downs we were decending below lowering cloud with reducing visibility.
I saw the picture and turned to go home.
It was rapidly deteriorating behind. No chance of getting home.
I diverted to headcorn and it was getting serious.
We made headcorn at 400ft agl across the countryside, in poor Vis.
I made a tight 400ft circuit and landed thinking we were very lucky to be alive. (There’s high ground and masts well above that)
The guy in the office gave me a Boll0£!+g.
I nearly punched him.
No other aircraft flew for 2-3hours
If we are within the aerodrome boundary for the purposes of landing, (effectively with permission from the owner) surely we only need to comply with any rules set by them or an explicit rule applied to the aerodrome by the authorities.
Richard Bach lamented that the ACME schools never taught precautionary landings. If you are scud running at 400’ AGL you should pick a nice field and land. So many fatalities from continued VFR into VMC which could have been avoided if the pilot had made a precautionary landing instead.
Have never heard of instructors requesting low level circuits as described – bad weather circuits are typically 500-600’ AGL.
The US has useful CPL ground reference manoeuvres but unless you are in a J-3 they are around 800’ AGL.
Balliol wrote:
Edit looks like a 300ft obstacle clearance for Cat A (from 90m ICAO?)
Yes, it is in PANS-OPS. Actually it is 295 ft.
Isn’t that a discussion of where the IAP designer can set the lowest circling height? That is relevant only to an IAP designer, and when he sets the min circling to X feet we have to fly it at (at least) X feet, no question.
What about the scenario I posted here?
Obviously in the circuit, no such minimum alt exists. But from there to do circuits at 200’ above the runway is way out IMO.
Except for mountain flying where 100 to 300 ft good weather circuits have been de rigeur since the technique for safe landing on glaciers and other slopes was established by Hermann Geiger.
The same is true for all off-airport landings and, to an extent, for unattended aerodromes. Are you sure you can see a badger hole or a roe deer or a discarded piece of fencing wire from 500 ft? And after running your main wheels over your chosen landing site, how will you assess the depth of your wheel tracks from 500 ft?
These are slightly unorthodox cases hence, I believe, the present wise choice of words in the Common Rules of the Air (instead of the UK CAA’s imprecise but potentially more restrictive reference to “normal aviation practice” – whatever that may be).
