I didn't say 50ft. It is 1/10th of the vertical speed at that moment which is at least 70ft to 100ft before MDA. It is sort of manual level off. Airbus prefers to do it this way and it works. However since you are going to fly level at that altitude it could also be done by setting that at FCU and allowing the aircraft to level off on its own. May be Airbus doesn't want to have a different procedure just for one type of approach.

And 50 ft would not be enough. It works probably for TOGA, but not for V/S=0 (there's a button for this mode on AB). One operator I know prescribed this at 100 above, immediately after the call from PM. It worked very well, no wonder as it is exactly the geometry provided above.

Sorry Vilas, I wasn't trying to imply you did. I was referring to your statement:

I, being a Boeing bloke, don't want to drift too much off thread; but why are Airbus making an easy job difficult by imposing these restrictions? Why not just let the pilot use the best mode for the job; or allow airlines to design their own SOP's within a/c design capabilities?
Is my ignorance of AB company FCTM procedures causing my confusion?

Is it not the case?

Our A330 FCOM simply states the following:

"MDA/DA shall not be set in the FCU ALT window."

No explanation is provided in the FCOM or FCTM and there doesn't appear to be any latitude when it comes to circling approaches. I don't know the reasoning behind the ban; as vilas suggested, perhaps it's because Airbus doesn't want to have different FCU altitude setting procedures for different types of approach. Or perhaps it's because they think the majority of non-precision approaches are flown as CDFAs and there are other ways to deal with the automation in the event of a circling approach.

In any case, levelling off at MDA for circling isn't difficult in an Airbus; it's just a matter of pressing the ALT button at the appropriate time. Just make sure you don't forget to do it and allow sufficient time for the aircraft to level off so you don't bust the MDA. That said, I believe the Boeing procedure provides an extra measure of safety that guards against distractions at the time you should be pressing the ALT button. In the B777, the MDA can be set to within 10ft on the MCP.

Anyway, this discussion is somewhat irrelevant at my outfit - we are no longer permitted to fly circling approaches!

This is from PAN-OPS DOC 8168 "Volume II Construction of Visual and Instrument Flight Procedures"

7.2.2 Parameters

The parameters on which visual manoeuvring (circling) radii are based are as follows:
a) speed: speed for each category as shown in Tables I-4-1-1 and I-4-1-2 in Chapter 1;
b) wind: ± 46 km/h (25 kt) throughout the turn; and
c) bank: 20° average achieved or the bank angle producing a turn rate of 3° per second, whichever is the lesser
bank. (See Figures II-4-1-App A-2 and II-4-1-App A-3 in Part II, Section 4, Appendix A to Chapter 1,
“Parameters for holding area construction”).

7.2.3 Determination method

The radius is determined using the formulas in Section 2, Chapter 3, “Turn area construction”, by applying a 46 km/h
(25 kt) wind to the true airspeed (TAS) for each category of aircraft using the visual manoeuvring IAS from
Tables I-4-1-1 and I-4-1-2 in Chapter 1. The TAS is based on:
a) altitude: aerodrome elevation + 300 m (1 000 ft); and
b) temperature: ISA + 15°.

The 25 kts is built in. TERPS also has 25 kts built in however there are other differences.

Not all Airbus have a level off button, to achieve this on a lot of A320s you would press the V/S, on the wide-bodies there is an ALT button or you can press V/S.

Your question has gone unanswered basically because there is no stable way to do what you are asking. You will be at 2300 ft above the runway, so you will want to start descending at 2300/318=7.23 nm track mile from the threshold, about 15 seconds after passing abeam the runway at 750 fpm at your 150 kts.

Practically you cannot do this in marginal conditions as you will not have the runway environment in sight late downwind. In marginal conditions the procedure while technically legal, is not not practically smart. In marginal conditions do the VOR-DME3 from the NW and "circle" to final where you can continuously have the runway environment in sight.

If you are actually flying down the ILS to do a cloud break, and your intention below the cloud ceiling is not to circle but to conduct a right hand visual circuit, as long as your company permits this, ATC clearance, required visual conditions etc there is no reason why you cannot descend down to 1500' on crosswind or downwind. Then fly a normal 1500 ft circuit to land, back to something sensible and you are used to.

There is no ICAO requirement to be within 30 degrees of the centreline, I have seen in the order of 13 different company variations for when a descent may be commenced, the ICAO requirement is to keep the runway environment in sight. On an airliner with the cockpit viability the way it is, gives rise to this sort of sensible constraint being put in place. In the Dalaman example raised above the VOR-DME3 is offset by 40 degrees making it a circling approach (more than 30 degrees offset), you can however descend down below the MDA on that 40 degree offset if you keep the runway environment in sight and have the required charted criteria.

Nothing stopping you having the circuit altitude set for a visual circuit.

swh
I was talking about A320 and wasn't talking about a separate button to level off but about the writing on the FCU panel next to the V/S button where it clearly mentions PUSH TO LEVEL OFF. Are you aware of any A320 that doesn't have this V/S button additional function?

RAT 5
Airlines have deviated from manufacturer's procedures and some of them had serious incidents because this is a fly by wire aircraft and the software and hardware used to achieve the design philosophy is not available to the airlines. So something that appears innocuous may or may not be so and you will be better off to check that with Airbus. Airlines can and do certain things differently but if they seek airbus approval it will be safer. Also airbus upgrades its aircrafts with better computers or equipment so somebody needs to keep track of that and modify the procedures suitably. Lastly an airline making procedures after careful consideration and individual pilot doing things differently is not same. That will lead to non standardisation.

@Nick 1: that's a good article. Thanks for posting the link.

There is no ICAO requirement to be within 30 degrees of the centreline,

Being an old fart, with depleted memory and a joy of basic flying, I remember an old edict that a circling approach was any approach where the approach track was >30 degrees from runway centreline. Thus, once within 30 degrees you were no longer circling and descent was at pilot discretion.

Our A330 FCOM simply states the following:
"MDA/DA shall not be set in the FCU ALT window."
No explanation is provided in the FCOM or FCTM and there doesn't appear to be any latitude when it comes to circling approaches. I don't know the reasoning behind the ban;

That to me is scary and indicative of todays pilots. (no offence to the individual). You receive an instruction that seems odd and you don't understand and you don't ask WHY. I've flown for various airlines and come across plainly daft/unnecessary SOP's. I asked the question, Why this and Not that?. No reply, just a blank gaze. As the operator gained more experience on the a/c the SOP's changed to guess what........

Why do pilots not question more, but just become sheep? They are the frontline guys not the desk jockeys. I once flew for a fast expanding airline where the CP lost his type rain for not flying the line, yet he was writing the SOP's. Give me strength.

All FBW Airbus have this feature. What is not common is the expedite button, that is an "ALT" button on a lot of aircraft.

There is no ICAO requirement to be within 30 degrees in order to descent below the circling MDA. The requirement is to maintain visual reference with the runway environment. There are a lot of circling approaches which puts an aircraft on an oblique base position where they can maintain visual reference with the runway environment.

The 30 degrees came from the final approach alignment criteria for straight in approaches in Cat A&B to be within 30 degrees of the centreline, and 15 degrees otherwise.

From PAN-OPS
5.2.2.3.1 Maximum angle. For a straight-in approach, the angle formed by the final approach track and the runway centre line shall not exceed:
a) 30° for procedures restricted to Cat A and B aircraft ; and
b) 15° for other aircraft categories.

These are some of the variations in industry that are widely used.

Only when visual contact can be maintained and on the middle of the base leg, never earlier.
• Within 30 degrees from the final approach track
• This depends on whether visual or have achieved circling criteria. This is
interpreted that you cannot descend below Circling Minima until you intercept
the nominal approach angle, or you declare visual – in the latter case the crew
become fully responsible for terrain avoidance.
• If the Circling minima are high (above 1500ft AAL - normal basic training
circuit altitude) some operators ask crews to ensure that the aircraft remain
within the protected area at all times. To achieve this it may mean descending
before the base turn is commenced to ensure a normal descent angle to
landing. Before leaving MDA certain criteria must be met. Ideally the RWY
environment should be visual at every stage of the descent but practically this
may not always be the case, particularly if the MDA is high or there is a
prescribed track associated with the circling manoeuvre. The really important
point is that we must assure ourselves that the predicted flight path of the
aircraft will remain in a clear area at all times with regard to both weather
and obstacles before a descent is commenced.
• The crew must maintain the MDA until the runway threshold has been
positively identified by the PF and that a normal FPA can be achieved to land
in the TDZ, a steep or a flat descent should not be attempted, if at any stage
the visual cues of the runway are lost, a missed approach should be initiated
• Generally, crew should stay at circling MDA/ H until necessary for approach
and landing; this is often on base leg. This is based on the height of MDA and
the interception of a normal glide path.
• Fly at circling minima (AP and AT engaged) all the way to the end of the
downwind leg and commence descent when turning bas.
• Landing threshold acquired by PF and the aircraft is in a position to carry out
a landing.
• It is important that the descent is to be made in a way to allow for a stabilized approach.
• Some operators require that the MDA be maintained until the aircraft has
manoeuvred to within a 30 degree angle of the extended runway centreline.

from http://skybrary.aero/bookshelf/books/1486.pdf

RAT 5, don't jump to conclusions. For your information I have asked 'why?' on several occasions, but haver never received a definitive answer. Our SOPs are mostly pure Airbus these days and would be the same as those of most other operators.

In any case, as I said in my last sentence: 'we are no longer permitted to fly circling approaches' so the answer is somewhat f@#$%ng irrelevant for our operation.

RAT 5
Your question
and you answered it yourself below:
That is why it is best left to the manufacturer or at least consult them before wringing in any changes. Nobody knows more about airbus than airbus. Ask them how and why by all means through your Flt. Ops. but don't be creative on your own. Curiosity may not kill the cat but it surely has killed or at least put in trouble some airbus pilots.
No more circling approaches! what is there to find out? An airline doesn't want to risk it or like the Indian DGCA simply doesn't permit it. That all. some pilots may have lost the thrill of doing it but isn't it a business after all? Company decides it.

We stopped doing circling approaches for a few reasons, but basically because we only fly widebodies and there is only one airport in our network where we might have had to do a circling approach and even then it was only a remote possibility. Nobody had done a circling approach in anger in living memory, and the only way to stay 'current' was in the simulator, which doesn't provide great fidelity for the late downwind/base turn bit. Management decided there was too much risk and that the simulator time could be better spent on other training, so our approval for circling approaches was taken away.

Yep; I take your point.

There is an interesting book just publisched " Handling the circling " ( the author is a retaired captain ) were is well explained with grafics and mats that , if you are required to be stablized at 3/400 ft with maximum bank of 25 in a circling with minima 600/2400 is impossible to have constant visual reference with the runway .

http://www.aviationcoaching.com/wp-c...ircling5-2.jpg

http://www.aviationcoaching.com/wp-c...ircling1.1.png

(Image from " Handling the circling " book)