Hi Bob and Rich

I had a question regarding minimas as your book says there are two visibility and MDAs for an approach in regards to the straight in visibility and circling visibility are these seperate one for night circling (bottom) and one for day circling (top)?

thanks just need things one cleared up!

Cheers
Linc

Thanks for your question Linc. It's a good one and it relates to an area that is often misunderstood. Actually I have often said that on a SI (straight in) approach plate the line labeled "Circling" should be labeled "Night circling" because, if you fly that approach by day and find that you are still in IMC at the published circling minima, you can still follow the procedure down to the straight-in minima.

Consider the scenario where, having arrived in the circling area below the published circling minima, you find that you cannot land straight-in because the runway is occupied, you are downwind, you are too high to land or the like.

Once you are established in the circling area, you can still circle by day under your own observation, maintaining 300ft (for a Cat B aircraft) clearance above any obstacle along your fight path and with visibility not less than the published circling visibility; (AIP ENR 1.5 para 1.7.6 Note 2)

For these straight-in approaches by day, providing you make it to the circling area with the circling visibility, you can ignore the published circling minima (which are based on the HIGHEST obstacle in the circling area) and circle, if necessary, 300ft above any obstacle you fly over.

This option, of course, is not available at night!

Thanks Bob clears things up!

Hmmm.... So, Bob, let me see whether I've understood your position correctly:

Let's take my home airport, Wagga Wagga (YSWG) for example. The ILS approaches for RWY 23 for Cat A&B specify:

• a straight-in minimum of 1030ft (shaded to 930ft)
• a circling minimum of 1710ft (shaded to 1610), with circling visibility of 2.4km.
• For reference, AD elevation is 724ft.

Let's say I'm conducting an ILS approach in IMC by day, and I break cloud at 1500ft with excellent visibility. I can carry on down the glideslope to to 1030ft (930ft if I have local QNH, which I usually will), and this will put me around 1nm from the runway - well within the circling area. But the wind is 20kt behind me, so I would prefer to land on RWY 05.

Bob, I think you're saying that because I've established visual reference within the circling area, I can now disregard the circling cloud minimum, and circle by visual reference, maintaining 300ft clearance, visibility better than 2.4km, and of course visual contact with the runway environment. You quote AIP ENR 1.5 para 1.7.6 Note 1(2), which says "When daylight exists and obstacles can be seen, the pilot has the option of descending from MDA from any position within the circling area while maintaining an obstacle clearance not less than that required for the aircraft performance category" - this in the context of 'During visual circling, descent below the circling MDA may only occur when:' (my underlining)

But ENR 1.5 para 1.10.1 says that "A missed approach must be executed if .... [d] a landing cannot be effected from a runway approach, unless a circling approach can be conducted in weather conditions equal to or better than those specified for circling;". And 1.7.3 says that "After initial visual contact, the basic assumption is that the runway environment .... will be kept in sight while at the MDA for circling." (my underline again)

So, my reading of the AIP would be that because my weather conditions (namely the cloud ceiling) are worse than the circling MDA, I may not circle (even by day), but must conduct the missed approach.

[and dammit - YSWG doesn't offer a 3D approach for RWY 05........!]

Austin, I presume that you are ramping up to your rating and don't have much/any I/F background to date. Never mind .. you'll learn the lessons along the way as you frighten yourself witless from time to time ...

Some general thoughts, if I may ...

(a) just because the rule book permits you to do something, doesn't necessarily mean it is a good thing to do. Particularly, in regard to close in circling, the terrain clearance concessions should be read to be used ONLY by those folks who know the aerodrome like the back of their hand, can name all the trees, cows and horses, etc. Suggest that you come back and comment again once you have found yourself in a min height, min vis, turbulent close-in circuit trying to keep the runway in sight, keeping track of the obstacles and so forth. This is just about the MOST difficult, highest workload exercise a pilot can be faced with ... absolutely NO fun at all. Fortunately, the situation doesn't arise all that often. On the other hand, a 0/0 ILS is a bit of a doodle .. something we routinely use to improve student scan rates and smoothness of control inputs in jet sim training.

Me, come below the published minima for circling ? Not in a pink fit. The hazards and risks are just too great. Keep in mind that the obstacle set is not guaranteed and, every now and then, someone finds an obstacle which the procedures designers missed ... do you REALLY want to trust your life to a pretty good, but not foolproof design system ?

On another anecdotal tale ...TAA, years ago, decided that the effort in maintaining the training requirements to permit crews to circle just was not worth the effort and risk. Their solution ? Proscribe circling. Ansett, on the other hand .. especially for the F27, kept the circling up. Really, it was never much fun scratching one's way around a low weather circuit in poor cloud and vis conditions ... any excuse was good enough to call it quits and hold/divert. Mind you, the training in fair weather was great fun .. just no fun when the weather gods had it in for you ...

(b) as to winging it on the fly .. a good way to kill yourself. If the,weather, or whatever, dictates landing on another runway following a runway approach to the circling minimum, you don't consider the straight ahead landing .. you have planned and will run with the circuit. If you have planned the straight in landing and the weather then dictates a change in plan half way down the approach, you are much better off flying the miss ... rebriefing yourself for the other approach and then doing it. Far too many folks have killed themselves and their passengers making it up on the fly.

Am I a bit conservative ? You bet I am ... and I'm still here and alive albeit that, in spite of being conservative, I've frightened myself witless on more than a few occasions over the years ...

No prizes for CFITs .. ever !

Consider another tale. Years ago, on the B727, going into HBA CAVOK late at night ... a pilot, with whom I had not flown before and had never been into HBA (but had lots of overseas flying experience), elected to fly the full runway approach ... that's conservative ... but puts a lid on a lot of the risks waiting out there to bite you on the delicate bits and pieces ... Sure it's a little bit different if you know the place intimately ... but you really have to assess than conservatively also ..

Hi John

Thanks for the reply. You're quite correct: I'm working towards my IREX exam, and I have very little IF background - just enough to know that I'd be petrified to do it anywhere near anything I might crash into. And as a low-time pilot, I'm always happy to benefit from the wisdom of those with experience, such as yourself.

That said, I'm not sure you've understood what I've said. I'M not the one arguing for coming below the published minima for circling; my interpretation is that the AIP prohibits that, though I think Bob is arguing that one could do it by first establishing visual reference below circling minimum on another approach (e.g. an ILS).

I certainly agree that there are many things the rule book permits that I wouldn't do in real life (like flying in IFR to YSSY with no comms squawking 7600 on the basis of 'last clearance' and a flight plan!). But I still need to know what the rule book permits for when I sit the IREX; that's why I'm looking for clarification, which - much as I respect your insight - I don't think you've provided. If you can, I'd be very grateful!

It was not my intention to answer the specific questions .. I'll defer to Bob on that. Rather, I sought to put in some real world considerations for your contemplation.

Maintain your evident conservatism and you may, in all likelihood, make old bones.

The old adage always applies .. there are old and bold pilots .. but very few old, bold pilots.....

[d] a landing cannot be effected from a runway approach, unless a circling approach can be conducted in weather conditions equal to or better than those specified for circling;".

I guess it all depends on what specified for circling means. Visually maintaining 300 feet above observed obstacles is specified for circling providing it's daylight and you are visual in the circling area [AIP ENR 1.5 para 1.7.6(e)].

However when it comes to an ILS approach, if you broke visual at or near the DA of about 270 feet, it would be difficult to explain how you would maintain 300 feet above obstacles during circling. In those circumstances, you would not be able to take advantage of para 1.7.6(e).

Hi Bob!

Thanks for the reply - as always, I'm grateful for, and impressed by, your untiring willingness to follow-up on questions from us beginners stumbling through the maze of CASA regulation....

I'd say the key phrase is 'weather conditions ... specified for circling '. Although descent to a 300ft clearance is a manouevre specified during circling, it's not a weather condition; and it's still based on the premise that you were visual and circling at or above the MDA to start with (see the lead-in to 1.7.6, and the subsequent Notes 1(1) and 1(2) ).

My read of 1.10.1 [d] would still be that one cannot even start to conduct a circling approach unless the weather conditions are equal to or better than the circling minima; and thus you wouldn't be in a position to take advantage of 1.7.6 (e).

(Of course, in practice - reinforced by John's words of experience - I wouldn't want to try it even if the regs DO permit it; but I'd still like to know which answer to go for come exam time!).

Some important points to ponder here, methinks.

Although descent to a 300ft clearance is a manouevre specified during circling, it's not a weather condition

One needs to read between the lines a bit. Considering the obstacle data integrity problem, why and when would a pilot consider dropping a little lower ?

(a) ragged base which is quite common. At the prescribed circling minimum, the aircraft might well be in and out of the ragged cloud mass .. a few feet lower and it might be a much easier workload for the pilot.

(b) due to the obstacle integrity consideration, ONLY at aerodromes where the pilot knows the locality like the back of his hand. In low vis it just is not feasible to fly while looking for, and avoiding obstacles ... plenty of CFIT prangs in the annals to support that view, I suggest.

So, yes, you may come down a bit .. but you would only exercise that option in very selected circumstances. In my view, very much a weather-related consideration.