Circling Approach rules
Do you have some backup for that Vilas? Its what I was taught, but I cannot find anything written down. The Boeing flight crew training manual for example is very vague about it. Do not descend below MDA until intercepting the visual profile to the landing runway is all it says. In the Dalaman case you are going to be well above the profile as far as I can see. Does anyone have any reference/company sops for such a case? My company certainly does not have anything.
"So in my Dalaman example you are going to fly 24 times 3 equals one minute 12 seconds past the abeam point before starting your turn?"
3 sec per 100' above ground. Fly 70 seconds in track and alt if you want.
Pan ops procedure design is based upon the maximum speed for that category being 205 kts IAS for CAT D converted to TAS for that height plus 25 kts for wind (236 kts in this case). Config 3 gear down you are not even close to that. Airbus also recommends the Vapp is inserted as a constraint on the FAF.
I don't make adjustments for wind, if it's beyond 25 kts it's beyond the design limits.
Turns are based upon 20 deg AoB or 3 deg/sec whichever is the lower.
3 sec per 100' above ground. Fly 70 seconds in track and alt if you want.
Pan ops procedure design is based upon the maximum speed for that category being 205 kts IAS for CAT D converted to TAS for that height plus 25 kts for wind (236 kts in this case). Config 3 gear down you are not even close to that. Airbus also recommends the Vapp is inserted as a constraint on the FAF.
I don't make adjustments for wind, if it's beyond 25 kts it's beyond the design limits.
Turns are based upon 20 deg AoB or 3 deg/sec whichever is the lower.
OK thanks so we are around 2.5 to 3 miles (at 150 knots) as we start the base turn. What happens now? in particular when do you start down and at what rate of descent. I have done a good few thousand foot circlings without embarrassing myself yet, but I cannot get my my mind round one from this height and distance (probably me, so tips from wiser heads appreciated).
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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?).
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?).
Last edited by Algol; 2nd Aug 2016 at 06:04.
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In according to Airbus we can't start to descend until the point where we can observe rw thr or some lights and so on,therefore base has to be performed without descending,just flaps full and try to find rw,when rw is identified-you have to start descending,just performing visual pattern,GS(+-10 kts per 0.1 gl/sl)/2 is Your v/s,d*3 is Your position on the gl/sl
I try to do it this way
Any other tips would be greatly appreciated
safe flights
I try to do it this way
Any other tips would be greatly appreciated
safe flights
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Algol
I think there is a confusion between the design process of circle to land and actual execution. The 25kt tailwind caveat earmarks the limit of the airspace that is available for circling from the point of terrain clearance. But when executing the circling within that airspace you still need to position the aircraft at a certain distance across on downwind and to a certain distance at the end of downwind for the base turn and that will not be same if you do not correct for wind. Without wind adjustment when turning downwind if you face strong HW you will end up very close to the RW and when turning base it will become tail wind and may blow you over when using the maximum permitted bank angle. Similarly the position at the end of downwind is determined by the prevailing visibility. The 25kt. tailwind design procedure may give you terrain clearance but runway may not remain in sight. So you need to adjust for wind but even that is subject to runway remaining visible throughout. There was a brilliant article on the subject by Capt. Eddie Foo in 2005 but I am unable to access it. It is also power point but that is not free.
I think there is a confusion between the design process of circle to land and actual execution. The 25kt tailwind caveat earmarks the limit of the airspace that is available for circling from the point of terrain clearance. But when executing the circling within that airspace you still need to position the aircraft at a certain distance across on downwind and to a certain distance at the end of downwind for the base turn and that will not be same if you do not correct for wind. Without wind adjustment when turning downwind if you face strong HW you will end up very close to the RW and when turning base it will become tail wind and may blow you over when using the maximum permitted bank angle. Similarly the position at the end of downwind is determined by the prevailing visibility. The 25kt. tailwind design procedure may give you terrain clearance but runway may not remain in sight. So you need to adjust for wind but even that is subject to runway remaining visible throughout. There was a brilliant article on the subject by Capt. Eddie Foo in 2005 but I am unable to access it. It is also power point but that is not free.
Algol:
Yes, you probably will sink below MDA if you don't commence the level-off until you actually reach the MDA. I would argue that a CDFA is a very different kettle of fish to a non-precision approach followed by circling. The CDFA is designed to mimic an ILS approach - you fly an approach with a constant descent angle to a 'decision altitude' (ie MDA + 50ft). On reaching the 'DA' you either continue the approach and land if visual, or execute a missed approach, taking care not to descend below the MDA. The aircraft does not fly level at any point during the final approach. The purpose of the 50ft buffer is to prevent the aircraft descending below the MDA while executing the missed approach.
The NPA that precedes a circling approach has one purpose; it allows the aircraft to descend to the circling minima for the purpose of executing a circling approach. It might be flown as a constant descent angle approach, but the aircraft can level off at the circling minima and then proceed to the missed approach point before executing the missed approach if not visual. You would certainly start levelling off before you reach the MDA, as you would when levelling off at any altitude, but there is no requirement for a 50ft additive to the MDA.
I agree with vilas regarding the requirement for wind corrections to the downwind timing. The 25kt tailwind component is part of the PANS-OPS design criteria used to define the radius of the circling area. The turn radius used to calculate the circling area is based on the aircraft's TAS plus a 25kt wind factor. The circling area is then defined by a radius that is twice the turn radius plus a fixed straight segment, centred on the runway thresholds. That is somewhat different to saying that the circling procedure includes a 25kt tailwind component; it doesn't. The downwind timing should be corrected for wind to ensure the aircraft turns base at the correct point and remains within the circling area.
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?
The NPA that precedes a circling approach has one purpose; it allows the aircraft to descend to the circling minima for the purpose of executing a circling approach. It might be flown as a constant descent angle approach, but the aircraft can level off at the circling minima and then proceed to the missed approach point before executing the missed approach if not visual. You would certainly start levelling off before you reach the MDA, as you would when levelling off at any altitude, but there is no requirement for a 50ft additive to the MDA.
I agree with vilas regarding the requirement for wind corrections to the downwind timing. The 25kt tailwind component is part of the PANS-OPS design criteria used to define the radius of the circling area. The turn radius used to calculate the circling area is based on the aircraft's TAS plus a 25kt wind factor. The circling area is then defined by a radius that is twice the turn radius plus a fixed straight segment, centred on the runway thresholds. That is somewhat different to saying that the circling procedure includes a 25kt tailwind component; it doesn't. The downwind timing should be corrected for wind to ensure the aircraft turns base at the correct point and remains within the circling area.
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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?
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Thanks for further info folks.
Vilas, I tend to agree with you about the 25kt increment - that it is a manoeuvre area limitation at design phase, but not meant to be considered for actual operation, where the ACTUAL wind should be adjusted for. BuzzBox says the same.
By the way I found that PowerPoint Presentation of Capt.Foo's - located here: https://www.scribd.com/doc/45970594/...cling-Approach
You can download it by right clicking on the first slide and selecting 'Save Page As'.
Its very useful and a good read.
BuzzBox, Regarding the 50ft increment - I agree with your comments, but I'm still a bit dubious on how to conduct that level off. If still in IMC at (say) 800ft in an approach with Circling Minima of 700ft you would need to start the level-off in order not to bust minima. But is that really acceptable if still IMC? Isn't a GA in fact necessary by then?
Vilas, I tend to agree with you about the 25kt increment - that it is a manoeuvre area limitation at design phase, but not meant to be considered for actual operation, where the ACTUAL wind should be adjusted for. BuzzBox says the same.
By the way I found that PowerPoint Presentation of Capt.Foo's - located here: https://www.scribd.com/doc/45970594/...cling-Approach
You can download it by right clicking on the first slide and selecting 'Save Page As'.
Its very useful and a good read.
BuzzBox, Regarding the 50ft increment - I agree with your comments, but I'm still a bit dubious on how to conduct that level off. If still in IMC at (say) 800ft in an approach with Circling Minima of 700ft you would need to start the level-off in order not to bust minima. But is that really acceptable if still IMC? Isn't a GA in fact necessary by then?
Anyone care to suggest what descent rate you need in Dalaman if you turn base at 2400 feet at three miles. The fifty feet increment presumably could be corrected downwind, but I am struggling with achieving a stabilised approach from high minima like this one.
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I can only speak from a practical view point and not a theoretical one. IMHO what we are trying to achieve is a safe practical approach & landing. I assume whether you are flying Boeing or Airbus you would elect to fly a circling approach, where the weather was near minima, using autopilot. It doesn't matter if you fly the initial approach via an LS or LOC; you round up the circling MDA - oo's and set it in the Altitude capture window. The a/c will 'start to level off' at a suitable height above that setting and then level off AT it. It should not bust it and there will be no sink and you will be above MDA.
Downwind, from abeam threshold, in a Cat C a/c I've always used 3sec/100' above threshold as datum and deducted 1sec/2kts tail wind. i.e. half the tailwind. A rate 1 level base turn. If you've made the correct spacing and turn radius you should roll out very close to centre line and on a 3degree GP. When you are about 90degrees to go you will be entering the +/-30 degree cone to the centre line where you can start a visual descent. You are now 'on finals' and terrain serration is Mk.1 eyeball.
Like I said, it seems to have worked for me over the years. There are one or 2 places where I question the use of the term circling. e.g. LEXJ RW29 Santander. The 'circling MDA is 2490' agl (2510' QNH) and the vis required is 2400m. Good game if you can't descend until on finals. I asked the chappie who writes the Airfield Briefs about this, as no mention/guidance was given about what to do. The SOP would be to set 2600' in MCP. You would not be visual at MDA with only 2400m. (Even the CAT D is 3600m.) These are standard category distances, make no sense and bear no resemblance to MDA, unlike a NPA CDA where the required Vis is related to the distance from RWY at MDA.
So there you are at 2600' and decide to fly level to the MAPT. You the see the required visual reference of the runway environment and commence circling for 75secs -1/2 tail wind. That will put you very close to the 4.2nm circle of safety. You now turn finals at 2600' and 4nm. That is twice the normal height and will need 1400-1600fpm just to get to the runway = unstable at 1000' & 500', unless you do 2000fpm PDQ. Equally, with 2400m vis you'd lose sight of the runway very soon after passing the threshold. All in all it is No Way a circling approach. It is a cloud break procedure for an extended visual circuit. The circuit takes you over the city, hence the height. All very confusing, but like I said, no guidance given and I'd expect total confusion to anyone who tried the conventional profile.
It sounds like Dalaman is similar. Not needed to do it in anger. Guess I missed something. Not one for the trained monkeys. Given that vis is an approach ban parameter, and circling is fraught with danger and vulnerable to total screw ups, IMHO it is not professional for the authorities to label such an approach as 'circling'. There will be places where 'get-home-itis' will sucker guys into scratching around on circling approaches in dodgy weather and hurtling at the runway in an un-stable manner. Not good.
Downwind, from abeam threshold, in a Cat C a/c I've always used 3sec/100' above threshold as datum and deducted 1sec/2kts tail wind. i.e. half the tailwind. A rate 1 level base turn. If you've made the correct spacing and turn radius you should roll out very close to centre line and on a 3degree GP. When you are about 90degrees to go you will be entering the +/-30 degree cone to the centre line where you can start a visual descent. You are now 'on finals' and terrain serration is Mk.1 eyeball.
Like I said, it seems to have worked for me over the years. There are one or 2 places where I question the use of the term circling. e.g. LEXJ RW29 Santander. The 'circling MDA is 2490' agl (2510' QNH) and the vis required is 2400m. Good game if you can't descend until on finals. I asked the chappie who writes the Airfield Briefs about this, as no mention/guidance was given about what to do. The SOP would be to set 2600' in MCP. You would not be visual at MDA with only 2400m. (Even the CAT D is 3600m.) These are standard category distances, make no sense and bear no resemblance to MDA, unlike a NPA CDA where the required Vis is related to the distance from RWY at MDA.
So there you are at 2600' and decide to fly level to the MAPT. You the see the required visual reference of the runway environment and commence circling for 75secs -1/2 tail wind. That will put you very close to the 4.2nm circle of safety. You now turn finals at 2600' and 4nm. That is twice the normal height and will need 1400-1600fpm just to get to the runway = unstable at 1000' & 500', unless you do 2000fpm PDQ. Equally, with 2400m vis you'd lose sight of the runway very soon after passing the threshold. All in all it is No Way a circling approach. It is a cloud break procedure for an extended visual circuit. The circuit takes you over the city, hence the height. All very confusing, but like I said, no guidance given and I'd expect total confusion to anyone who tried the conventional profile.
It sounds like Dalaman is similar. Not needed to do it in anger. Guess I missed something. Not one for the trained monkeys. Given that vis is an approach ban parameter, and circling is fraught with danger and vulnerable to total screw ups, IMHO it is not professional for the authorities to label such an approach as 'circling'. There will be places where 'get-home-itis' will sucker guys into scratching around on circling approaches in dodgy weather and hurtling at the runway in an un-stable manner. Not good.
Great post RAT 5 and exactly my view, there is not a one size fits all solution. About the only times I have recently flown a circling are when the wind went out of limits at the last moment having prebriefed, Adana anyone? You need to apply common sense. p.s. I have observed from the holding point some extraordinary circuits (given the terrain) that people have flown in places like Pristina.
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Fully agree with that point about cloud break procedure only. I'm not familiar with that Santander approach, but Circling seems to only make sense as exactly what you describe - a cloud break to visual.
That's really all they're good for if you ask me. Anything more marginal (e.g. very poor vis below cloud) has to be seriously questionable in this age of RNP Approach capability.
By the way, Airbus don't allow setting the MDA in the ALT window.
Not anywhere I've ever worked on them anyhow....
That's really all they're good for if you ask me. Anything more marginal (e.g. very poor vis below cloud) has to be seriously questionable in this age of RNP Approach capability.
By the way, Airbus don't allow setting the MDA in the ALT window.
Not anywhere I've ever worked on them anyhow....
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To be fair, guys, I have done 600' circling as per profile, at night, and it worked great. I've also done it at 1000' in/out cloud in the day. Both were legitimate profiles and we landed 'sans drama'. It does work when required. My real point is that if 2400m is the required vis for circling, and I would not like to include the approach lights in the assessment of keeping the 'runway in sight', then anything above 500' is marginal in that. You could scratch at 600' possibly. Given that the minimum circling is (an absolute 300' above and obstacle & 400' all ????????) it doesn't give much extra. Therefore 2400m & 800' don't match. Consider also that some airfields do not have omni-directional lighting and they are damn near invisible downwind. Good game.
I once flew under an XAA, pre-JAA, that increased our circling vis to 3600m. They calculated the parallel distance to make a rate 1 turn radius not finals and concluded it was greater than 2400m. This profile is such a simulator theoretical 'tick in the box'. Overtime I had to do one for check the Wx. was MDA +100' and 8km; never 3000m. It was not effective realistic training'. It was effective in flying a profile that worked, almost IFR/dead-reackoning, and delivered you onto finals, but it did not simulate a real ****ty night in the clag with terrain around.
I once flew under an XAA, pre-JAA, that increased our circling vis to 3600m. They calculated the parallel distance to make a rate 1 turn radius not finals and concluded it was greater than 2400m. This profile is such a simulator theoretical 'tick in the box'. Overtime I had to do one for check the Wx. was MDA +100' and 8km; never 3000m. It was not effective realistic training'. It was effective in flying a profile that worked, almost IFR/dead-reackoning, and delivered you onto finals, but it did not simulate a real ****ty night in the clag with terrain around.
Dalaman now has a variety of approaches on RW19 which can be used at night depending on your airline and aircraft type. The LOC approach has a 4 degree descent profile.
If still in IMC at (say) 800ft in an approach with Circling Minima of 700ft you would need to start the level-off in order not to bust minima. But is that really acceptable if still IMC? Isn't a GA in fact necessary by then?
For example, the VOR Rwy 16 at Fukuoka in Japan is based on the DGC VOR, which is located 5.5nm before the threshold of Rwy 16. The missed approach point is located D5.4 after DGC, ie just before the threshold of Rwy 16. If you were intending to circle for Rwy 34 in a Cat D aircraft, you could theoretically descend to the Cat D circling MDA (1030ft), then fly level at the minima until you reach the missed approach point, then execute a missed approach if still IMC.
By the way, Airbus don't allow setting the MDA in the ALT window.
But on a Circle, where, as pointed out by Buzz, there is no need (in fact it is undesirable) to do a Go Around if not Visual when first reaching the MDA, ideally the ALT SEL would be set to the MDA and the aeroplane allowed to level off automatically. The Missed Approach altitude is the preset in the ALT SEL. Circling approaches in my "Boeing" are done just that way.
If you are not allowed to set the MDA in the ALT SEL, then you're stuck. 50ft above MDA may not be enough when pushing the button, as described by Vilas.
Agreed. Airbus' outright ban on setting MDA is a bit silly IMHO. To my mind, it makes sense to set it in the case of a circling approach, as done on the Boeings. That said, the MDA could only be set to the nearest 100 ft (unlike the 777!), so you would have to level off above the MDA unless the MDA happens to be X00 ft, as RAT5 mentioned above.