Circling Mins

[NVpilot]

I was taught not to leave the MDA on a circling approach until in a position to land, usually on a base to final segment, some people have a different philosophy, whereas once you have the field in sight you may descend and maneuver as needed below the published MDA.

Confused.

[RYR-738-JOCKEY]

On a circling you have min 400' obstacle clearance within a radius from the field according to category, f.ex. 4,2 NM for cat C aircraft. You are obliged to keep this until you can safely execute a normal visual descent to touchdown.
The obvious thing here is you cannot start the descent before being abeam threshold, and of course no later than outside the applicable radius. Every company has its own procedures.
A rule of thumb:
1:Start timing abeam
2: at 3xMDH(in hundreds)+-wind: Start a slow descend.
3: Intercept PAPI

[westhawk]

It is also worth noting that the point where a descent from MDA should be initiated will be affected by the height above the rwy, the groundspeed and the required descent gradient. A 500' HAA MDA would normally call for descent to begin no further than about 1 1/2 track miles from touchdown to achieve a 3 degree descent at 140 or so knots. this would normally occur with less than 90 degrees of turn remaining to line up on final. With an MDA of 1000' HAA, the descent would have to begin about 3 track miles from touchdown. In order to remain within the protected airspace and maintain at least a 3 degree descent angle, descent initiation would need to occur somewhere on the downwind portion of the maneuver. Some mountain airports have signifigantly higher MDAs which require even more track miles to descend at anything approaching "normal" rates.


Best regards,


Westhawk

[OzExpat]

So what happens when the circling MDA for your category is governed by an obstacle at the extremity of the protection area, or even on the opposite side of the aerodrome, if there's no circling restrictions? I don't know how Pans Ops is interpreted in other parts of the world but, here, I can descend - provided that I have visual reference - to an altitude that gives me the standard obstacle clearance height for my category.

It certainly helps if you know the aerodrome and the obstacles in the vicinity. However, if you're visual and have good visual reference from the cockpit (obviously some aircraft aren't as good as others in that regard), and can identify a height of 300, 400, 500 etc feet above an obstacle, you can often descend a bit sooner in complete safety, if necessary.

Of course, as I said at the outset, it's a matter of how Pans Ops is interpreted in your part of the world.

[RatherBeFlying]

The protected areas are much smaller in procedures designed to Terps criteria as a 767 driver found out the hard way: http://www.pprune.org/forums/showthread.php?t=50274

[OzExpat]

Yes RBF, that's one of many reasons why I confined my comments to Pans Ops.

[RatherBeFlying]

OzEx -- no criticism of your earlier comment.

It's just that the record shows that Terps circling minima and jet transports don't work well together without thorough site-specific training -- GA does not do that well either.

So the very first thing anybody may want to check before accepting a circling approach is whether it's Terps or Pans Ops -- and maybe think of going somewhere else if Terps.

[westhawk]

So the very first thing anybody may want to check before accepting a circling approach is whether it's Terps or Pans Ops -- and maybe think of going somewhere else if Terps.

RBF:

Let me start by saying that I am by no means a Terps defender or advocate. It is simply the standard that the approaches I am accustomed to flying are designed under. With that being the case, I have endeavored to learn what I can about how approaches are designed, but there is room for much more learning. Early on, it became apparent to me that there is little room for error and that none should be expected. What follows is just some of my observations related to the conduct of circling approaches. My comments are intended as "food for thought".

It should go without saying that careful analysis of each instrument approach procedure is prudent prior to beginning an approach. Additional planning and briefing is necessary when a circling maneuver will be required. Obviously, if it cannot be determined that the aircraft will remain well within the protected airspace or that any other condition exists which casts doubt on the safety of the maneuver, it should not be attempted.

That said, it should be understood that instrument approach minimums are just that. Minimums. Pilots and their employers retain the right to adjust them upwards. It may not always be prudent to execute an approach to minimums just because it meets "legal" requirements.Terps obstacle clearance protection is of smaller size than Pans Ops and without allowance for the effect of winds or TAS adjustments for altitude. These variables must be accounted for and applied by the flight crew.There is no allowance for flying outside the protection area. Large deviations outside the protected area should be considered suicidal. With all this in mind, it should be apparent that circling approaches designed under Terps criteria must be flown according to a well thought out plan and must be flown accurately. Allowance for known variables must be applied and a descent point identified. The flight path to join the missed approach procedure while remaining in protected airspace must be briefed. The limitations of the obstacle protection provided must be understood and respected. The same might be said of any procedure. If there is any doubt that this can be done, the plan should be scrapped and a less critical procedure or perhaps another airport selected.

The FAA has been considering the adoption of Pans Ops equivalent standards for many years. The argument against appears to concern the loss of utility projected to occur as the result of the higher minima which would be required as a consequence of the larger obstacle protection areas dictated under this standard.

As a pilot who has executed a fair number of Category D circling approaches, I will say that I wish that Terps approach design criteria were a little more widely known in the pilot and training community and that training in the planning and conduct of circling procedures were emphasized to a greater degree. Not that it isn't done at sim training. It is. But circling is just one of many items that must be accomplished in a very limited amount of time. As it stands now, it is largely up to pilots to learn the nuances for themselves, of their own volition. So I respectfully suggest that we either assure that we are fully prepared to plan and execute circling procedures within the limitations of the design and our ability to execute it under the prevailing circumstances or be prepared to follow the advise in the quote that begins this post. There is little room for error or uncertainty.

Best regards,

Westhawk

[OzExpat]

Yes RBF, I completely agree with what you and Westhawk have said about TERPs circling criteria. I'm also aware that the FAA has been wrestling with that criteria for quite a while - in fact, it was brought into very sharp focus by a rather messy prang, some years ago, involving a Bisjet (I think it was) using a circling approach in lousy weather in Colorado.
The argument against appears to concern the loss of utility projected to occur as the result of the higher minima which would be required as a consequence of the larger obstacle protection areas dictated under this standard.
The opposing argument is the greater safety and greater flexibility that is available when using more realistic circling area dimensions. Yes, sure, there's every chance that circling MDA will be increased by the larger circling area, but I've always reckoned that this was the very reason why the TERPs circling area criteria is unrealistic.
As a Pans Ops procedure designer for most of the last 20-odd years, in a place where circling MDA is often quite high, I've found some flexibility in the use of it's circling criteria that has allowed a reasonable compromise between circling area dimensions and aircraft maneouvrability, especially for Cat. D and the larger Cat. C aeroplanes. I think that the FAA's real problem is that they'll have to put in a LOT of design effort which could cost them a lot more than they'll ever be able to recoup. I hope that I'm wrong about that but I fear that the real argument relates more to dollars and cents than to safety.

[westhawk]

OzExpat:

Here (http://www.ntsb.gov/publictn/2002/AAB0203.htm) is tG-III crash you referred to in case you find yourself with time for some light reading. While a circling maneuver was not a factor in this crash, the VOR/DME to Aspen is a circling approach. This very issue of terminology was a factor as you will see near the bottom of the report.

While I would certainly have no issue with the adoption of Pans Ops approach criteria in the US, I too don't think it will happen any time soon. As well as the reasons you state, I would add that the big push these days is to commission more straight-in RNAV/GPS approaches including WAAS enhanced LNAV/VNAV. Precision GPS approaches to ILS equivalent minimums are just around the corner if funding is provided. The FAA seems quite committed to this. WAAS upgradable boxes are selling like hotcakes. There's no solution more popular with government than one which requires new hardware! We'll see what happens. These new approaches ARE pretty slick though.

Best regards,

Westhawk

[jonny dangerous]

Interesting points all, especially from WestHawk and OzExpat and RBF(does the learning ever stop?!).

I have night time trip to Manzanillo, Mexico later this month. Have flown the visual approach daytime there several times, but til now, not at night. In light of the comments above, I've been looking at the circling approach for RWY 28, the runway with the PAPI.

My question is how would I determine if Pans Ops or TERPs were the design criteria (We use Jepps)?

Then I'll have to figure out what you two are talking about;) !

PostScript: just pulled out our Intl Ops guide. It has a good primer on this stuff. Thanks for bringing the topic up...

[OzExpat]

Right on the money again Westhawk! :ok: When you talk about RNAV/GNSS you're talking to a bloke who's a dyed-in-the-wool supporter! The only problem in my part of the world is that I'm faced with many major airports that have significant terrain problems that can't even be solved by installing an ILS. Thus I'm forced to employ cirlcing approaches, with circling restrictions, for the sake of getting a usable MDA.

The problem with this is that some of the datacard manufacturers refuse to include circling approaches in their database. Thus, the companies that need these approaches normally end up having to enter into a special (read "higher price") relationship with Jeppesen to have the approaches coded onto their own cards. I've never been happy about that but, then, I understand the litigation argument of the datacard manufacturers in regard to circling approaches.

Thanks for the link to the Aspen prang. I'd read it quite some time ago, but the intervening quantity of booze made recall a tad difficult. ;) Reading the report brought the memory flooding back, so thanks for that.

jonny... as far as I know, Jeppesen identify Pans Ops criteria on all the charts they reproduce, when the procedures are designed to that criteria. If this is correct (I've only seen Jepp charts for a very small proportion of the world), I assume that the absense of this identification would mean that the procedure is designed to TERPs criteria.

Perhaps someone who has broader experience of Jepp charts will be able to give a better answer?

[OzExpat]

Just to add to my previous post Jonny (for some reason the "edit" fuction didn't want to work for me :{ ), while waiting for a better answer, it's probably going to be much safer to take the worst case scenario. This will be TERPs, for circling anyway.

[RatherBeFlying]

the big push these days is to commission more straight-in RNAV/GPS approaches including WAAS enhanced LNAV/VNAV:ok:

The salient difference between a straight in and circling approach is that with circling the final stage of the approach design task is dumped upon the crew at MAP, the most critical segment. WAAS enhanced LNAV/VNAV approaches give the crews a completed design.

Add to that that airports without straight in approaches tend to have terrain constraints that are often invisible at night as pointed out by the Aspen report Westhawk has kindly posted: Although this accident occurred only 7 minutes after the end of evening civil twilight and the beginning of night, the mountainous terrain created twilight and nighttime conditions much earlier. The controller-in-charge stated, in a postaccident interview, that the sky was "very dark" in the minutes before the accident. In fact, the Safety Board calculated that the sun had set below the mountainous terrain about 25 minutes before the official sunset time60 and that evening civil twilight ended about 1830 rather than 1855. Also, the shadow for the ridge immediately to the west of the accident site would have crossed the accident site 79 minutes earlier than official sunset. As a result, the dark conditions would have significantly degraded the flight crew's ability to see and safely avoid terrain while making the visual transition from the instrument approach to an intended landing. The reduced visibility and light snow showers near the airport would have further degraded the flight crew's ability to see and safely avoid the terrain.
This accident reveals that the aeronautical definition of night does not adequately take into account darkness in mountainous terrain. Specifically, because pilots do not have sufficient ambient lighting to see and safely avoid unlighted terrain during periods of darkness before official night, the night restriction on the VOR/DME-C approach is not enough to ensure safety of flight. Thus, nighttime restrictions may not sufficiently mitigate potential hazards associated with flight operations into ASE and other airports with mountainous terrain during periods of darkness.61
61 To address this issue, the Safety Board issued Safety Recommendation A-02-08 on April 15, 2002. Safety Recommendation A-02-08 asked the FAA to "revise any restrictions and prohibitions that currently reference or address `night' or `nighttime' flight operations in mountainous terrain so that those restrictions and prohibitions account for the entire potential period of darkness or insufficient ambient light conditions, and establish a method to clearly communicate to flight crews when such restrictions and prohibitions apply."

[OzExpat]

G'day RBF,

I'm old enough to remember a time when instrument approach charts in Australia differentiated between day minima and night minima by 200 feet! I'm not, however, old enough to know whether or not this was originally mandated by ICAO but I suspect not. I do know, however, that the "infinite wisdom" of ICAO came to the fore with Pans Ops 1986, wherein the environmental factors that had to be considered in declaration of DA/MDA did not include night time.

I live in a place where the daylight and darkness graphs have little bearing on reality. The division between these two extremes is neither slow nor subtle. In fact it's more like... one minute there's sunlight and the next minute there's darkness. The cut-off is, of course, due to the effect of mountain ranges which, in general terms, form the backbone of the mainland and all of the larger islands.

Whether or not there should ever have been a compensation for that is open to conjecture. The point that needs to be made, however, is that there is no evidence that the difference has ever contributed to an incident/accident here (at an aerodrome with instrument procedures).

What I'm saying, I guess, is that pilots are given a certain amount of credit for intelligence around here. This is because they are all aware of the problem and well accustomed to it. There isn't a lot of night flying around here and the few places that are available for it have runway-aligned approaches that serve the RWY end that is most likely to need the instrument approach.

Now that's probably a new concept to some folks on here but the fact is that there's 2 kinds of weather - and 2 kinds only - here. One kind blows from one consistent direction and brings (for the most part) reasonably good visual approach conditions. The other kind blows from the reciprocal direction (or close enough to reciprocal) and is more than capable of producing the sort of weather that requires an approach right to MDA.

That's a fairly simplistic summary of a rather complex subject regarding tropical weather, but it's enough to highlight the difference between a place like this and a place like Aspen. I suspect that the problem in the USA is that charter and corporate pilots go anywhere at a moments notice, so to speak, and therefore have little time to familiarise themselves with local conditions at any specific destination.

This is a problem for crews that don't often venture into places such as Aspen. The approach in question was very complex and therefore required crews to devote a great deal of time to briefing it. While that fact should've been enough to alert the crew to the reason for the complex approach, it's easy to understand how this vital clue could be overlooked.

Now then, the FAA system also gives pilots a lot of credit for intelligence, but the simple fact is that there are a lot more pilots, and a lot more charter and corporate companies, in the USA than exist here. And there is much more competition there too. I won't say that the aviation system encourages this because the same would be true here and the accident statistics are vastly different.

I'm not suggesting that the FAA should consider the "night MDA" concept, as previously used in Oz, not even for airports in mountainous areas. It might have made a difference in the prang in question but, overall, I doubt that it would contribute anything other than a lot more missed approaches after the sun has set. I think that, despite the wording of the recommendation, the NTSB has a valid point.

The point probably should be that there needs to be an education program, perhaps compulsory, for pilots to understand that the difference between night and day on some of the (TERPs) circling approaches needs to be understood in the wider context of visual approaches after actual sunset. This is most certainly the most hazardous time, when unlit obstacles cannot be readily seen and will, therefore, be capable of wreaking havoc with any visual approach when visual conditions really don't exist.

The real problem here is, of course, that the design criteria (whether TERPs or Pans Ops) does not require all obstacles to be shown on an approach chart. Instead, the obligation is placed squarely on the pilot-in-command to have made an assessment, based on topographical charts (and local knowledge), prior to using any instrument approach. The difficulty with this is immediately apparent because, after all, who would bother to do so for an ILS approach? Yes, a precision approach is much different to a non-precision approach but the fact is that the design criteria makes no differentiation in the obstacles that need to be shown on the chart.

Large airlines have the capability to make those assessments and the responsible ones do so. Smaller companies - charter and corporate - are unlikely to have the resources for that. Thus it generally falls to the command pilot to do the necessary homework - and to do it without the advantage of knowing the details of the design criteria. Perhaps there will be a "duty of care" responsibility one day, but I suspect that it won't happen any time soon.

Thus, for many such operations, the only safe course is :- when in doubt, don't push your luck - go around and divert. That'd be a bitter pill to swallow, especially in the competitive US charter market but, until technology allows more runway-aligned approaches at difficult locations like Aspen, it's the only safe game to play. In the meantime, a public education program for pilots about the hazards of night visual approaches from circling procedures seems like the only viable option.

There's been no formal education program here but, as previously said, this is an environment where the difficulties are already well known and incorporated into line training. Thus it can be said that there has been an on-going education program here for many, many years with the result that we don't see accidents of this sort. On that basis, I'd have to say that an education program is likely to be successful in reducing the incidence of sad occurrences such as the one at Aspen.

[jonny dangerous]

In the meantime, a public education program for pilots about the hazards of night visual approaches from circling procedures seems like the only viable option.


Consider me as enrolled in the program. Thank you all for your postings here. It really has got me off the couch and into the books for more info on this topic.

I've taken night visual approach from circling procedure out of my bag of tricks for the time being. At the aerodrome I mentioned above, the circling procedure is fine during the day...at night, I'll use the other resources and options available.

[Dan Winterland]

Generally, TERPS is the standard for Jepps, but if they are written to PANSOPS standards they say so on a plate, usually by the minima on approach plates. However, this is not the case for all of them - so beware.

But another method is to know what standard the country you are flying in uses.

The USA, Canada, Central and South America, Japan, Taiwan and Korea use TERPS. Everwhere els uses PANSOPS except for military airfields in the Phillipines and Thailand, although I think the Thai military may have just swapped over.

[OzExpat]

To complicate the matter just a bit, Dan, the last I heard about Korea is that they use TERPs at some aerodromes and Pans Ops at others. :eek: Are we all confused yet? :uhoh:

[Centaurus]

A night circling approach where you may be able to see the runway on downwind or base but where you cannot judge the height between you and the terrain in your projected flight path, is relatively safe until the moment you elect to descend below the published circling MDA for whatever reason. From that moment on you are entirely responsible for your own obstacle clearance. The lawyers of the passengers are waiting in the wings.

If you cannot absolutely guarantee safe terrain clearance, but nevertheless choose to commence descent below the published MDA on downwind or base in order to ensure a stable approach, then may Lady Luck be with you.

Far safer to hold MDA until guaranteed obstacle clearance within the landing approach splay. If this also means your final approach is unstable in terms of speed, rate of descent, power setting etc, then this again becomes your problem. Either go-around or don't attempt a circling approach under these conditions in the first place.

[AerocatS2A]

So what happens when the circling MDA for your category is governed by an obstacle at the extremity of the protection area, or even on the opposite side of the aerodrome, if there's no circling restrictions? I don't know how Pans Ops is interpreted in other parts of the world but, here, I can descend - provided that I have visual reference - to an altitude that gives me the standard obstacle clearance height for my category.
It certainly helps if you know the aerodrome and the obstacles in the vicinity. However, if you're visual and have good visual reference from the cockpit (obviously some aircraft aren't as good as others in that regard), and can identify a height of 300, 400, 500 etc feet above an obstacle, you can often descend a bit sooner in complete safety, if necessary.
Of course, as I said at the outset, it's a matter of how Pans Ops is interpreted in your part of the world.
I assume your part of the world = PNG?

The rule, as written, in Australia is that at night you must maintain the MDA until intercepting your normal descent profile for the circuit. During the day you may descend sooner, BUT, you must maintain the maximum practical obstacle clearance. What that means is that you may descend below the MDA as necessary to stay visual, but you must maintain the minimum obstacle clearance (obviously) and you mustn't descend any more than you have to to stay clear of cloud.

[OzExpat]

My post omitted 2 rather important words... "by day".:uhoh: