IMC rating recommended minima?

[Fright Level]

Thank you all for the healthy discussion on this. I'm really trying to concentrate on the law and numbers (after all, flying is a numbers game).

Pace is quite correct, cloudbase is a subjective thing and what the man in the tower sees is not the same as the pilot sees (at 285 feet, even the tower at Heathrow is higher than their Cat 1 minima). I have flown many times in conditions of low cloudbase where the base is not uniform so it could quite easily be possible for the tower to report 200 feet but it being higher over the approach and numbers. Once you are clear of cloud and can continue the approach with continuous reference to the surface, it matters not if the cloud was angled at 4 degrees and was only 100' over the centre of the runway. So, tower reported cloud is not a legally binding reason to throw away an approach.

On the subject of visibility, this is defined as "flight visibility". The ANO says Flight visibility means the visibility forward from the flight deck of an aircraft in flight, however, the ANO does then comment "For the purposes of an aircraft taking off from or approaching to land at an aerodrome within Class B, Class C, or Class D airspace, the visibility, if any, communicated to the commander of the aircraft by the appropriate air traffic control unit shall be taken to be the flight visibility for the time being."

Some refer to RVR but this is measured by 3 transmissometers alongside the runway (touchdown, midpoint and stop end). RVR's are not reported when the vis is above 1,500m so if the tower are reporting all RVR's below 1500m then the IMCR is subject to an approach ban and can't descend below 1,000' above the airfield/past the FAF etc.

If the reports were, say, >1500/1200/900m (TD/MID/STOP) then the pilot could use his assessment of the visibility at decision height, then continue the approach and land. There is no law against taxiing in low visibility, so the mid point and stop end are not important for a light aeroplane that can be demonstrated to stop in the first third of the runway (pedantic I know). The ANO refers to the RVR being above minima for the relevant RVR. The stop end RVR is not usually relevant for a light aircraft on landing. (Assuming that RVR transmissometers are usually installed at airports with runways >2,000m). You could therefore argue the midpoint isn't overriding either.

IO540 says the AIP is not the law but I would not fancy my chances in court against the CAA if it could be shown I breached something that was even a "recommendation" in the AIP, which are after all guidelines and information published by NATS. You mention the autopilot and there are higher limits for single crew ops unless an autopilot is installed but these won't apply to SEP pilots because of the more restrictive SEP limits (when under public transport). Again, if you fly below PT limits on a private flight, you're opening yourself up to potential problems if something went wrong. Better than the IMCR advice of "add a bit if you're not current", the public transport rules add better clarity to what limits should be used.

I don't have my KAP150 or a/c POH to hand. What is the minimum height for your autopilot engagement on take off/landing? I too have watched one fly down to 200 feet in VMC but found it a bit agricultural in coping with even light crosswinds in the latter stages of the approach (ie <500'). If it was mist/fog I'd trust it with close monitoring, if it was a gusty night in heavy rain, I'd go somewhere else.

I agree that setting personal limits is vital, but it's important that every pilot knows what the absolute legal minima is. With your help, I've found the info, thanks!

Edited to add: IO540 says since almost nothing (short of total fog) stops CAT going to a destination.

In fact forecast arrival fog rarely stops (long haul) Cat 3 equipped (ie most) commercial flights departing, they just carry appropriate fuel. What does stop them departing on more occasions are strong wind forecasts (eg typhoons in Hong Kong). In a short haul environment, fog over Europe can often be widespread and wipe out both departure and destination or cause such long ATC delays whilst LVP's (low vis procedures) are in effect that flights are scrubbed. It's not the low visibility that gets them for they can operate quite happily, but the economics of potentially holding at OCK for 80 minutes on a 30 minute sector.