Circling Approach rules

[Algol]

Thanks for all the replies, sorry I've been too busy to take part since my OP.

Regarding the +50' on MDA - we do a Circling Approach because the desired landing runway has no instrument approach (and is IMC), and/or because the only instrument approach runway has an out of limits tailwind for landing. We use the instrument approach just to get visual contact, then manoeuvre visually to the desired landing runway.

The initial instrument approach may be an ILS, but may be (certainly likely in the SIM) an NPA. Since most NPA's these days (mandatory in my company) are flown as CDA's the published MDA of such approaches must be incremented by 50' to allow for GA sink (in order not to bust the minima).
But I'm being told its not necessary to increment Circling Minima.

So, this is an approach of two parts. First the 'let down' to visual contact, then level off, break off, and Circling.

Airports which have circling approaches will have published Circling Minima, which guarantee obstacle clearance during the manoever. You must stick to that during the visual manoeuver, and it is not required to increment it since it is flown level (no sink, hopefully!).

However, the instrument approach to the circling minimum (which may be a CDA flown NPA) may well (certainly in the SIM) be a marginal 'cloud break' approach.
Adding 50ft might well keep you from 'breaking out' and seeing the runway.

But my question is - since you are normally required to add 50ft to the CDA flown NPA minima, why would it not be required here too? Aren't you likely to sink below the MDA if you commence level-off (for circling) AT the MDA?

I am guessing its not required because the circling approach minima are already higher than the published 'straight-in' approach minima? But does that really permit you to sink below it all the same?

The second part of my question related to timing the approach.
As several posters pointed out, the manoeuvre is designed to be visual primarily, but the 'template' timings given are meant to keep you within the tight circling boundaries designed for the airport/runway.

Since the most likely reason you are circling is that the tailwind on the instrument approach runway would prohibit a landing, you are almost certain to have a tailwind on the circling (downwind) leg. That could stretch the downwind leg beyond the circling boundaries and lead to disaster (e.g. Air China at Busan).
The standard timing is meant to help prevent that.

In my current company I'm being told there's no need to correct for wind in threshold timing during circling, because 25kts tailwind is already built into the standard 30secs timing.

In my previous company we were given a standard circling timing of 20 secs from abeam the threshold of the landing runway (at 500ft circling) with an increment of 3 extra seconds for each 100ft above that). A further WIND correction of +/- 1 sec/kt of wind was to be included.

No mention was ever made to me of a 25kt tailwind built into the design (this company was PANS-OPS).

I have the FCTM for another major and reputable carrier based in Asia which also includes a +/- wind correction on threshold timing*. This would seem to infer there is no 25kt TW built in their procedure either.

I'm sceptical of this 'no corrections' policy, and that's why I sought opinions here.

The big problem I forsee is if the 25kt tailwind isn't there, will you be turning in too tight to stabilise in time?

Nick1, thanks for that article on circling approaches. Very interesting - although it's TERPS related primarily, more suited to US operations. I especially found it interesting that the author pointed out that under current design the standard circling approach construction sets you up for failure.

Thanks also for the idea about a Fix Info at 45deg from threshold. Sounds workable, but not sure if it would be accepted in a PC, and how it would even relate to the timing limits.

Overall this type of approach seems to be still a big 'grey area' with many different standards and designs, and SOPs, which makes me uneasy.

(* Both of the FCTM's I have date to around 2010, and I believe the TERPS Circling Manoeuvre was re-designed in 2012 according to Nick1's article. Were all such manoeuvres re-designed then to include the 25kt tailwind?).