Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

How does your company describe circling approaches?

Tech Log The very best in practical technical discussion on the web

How does your company describe circling approaches?

Old 6th Dec 2013, 08:10
  #1 (permalink)  
Thread Starter
 
Join Date: Feb 2004
Location: -
Posts: 206
How does your company describe circling approaches?

Hello all,

I would like to know how other companies describe the circling approach procedure, specifically the base turn to final from downwind. In my lot, with orange aircraft(Cat C), we start the stopwatch abeam the threshold as we pass downwind, timed 3 seconds per 100ft AAL corrected for wind. And then turn base.

The reason I am wondering about is to do with the protected area and the tightness of the turn to final. Cat C aircraft will have 4.2nm to manouevre inside safely. And this is based on a max speed of 180 knots with a 25 wind plus correction for TAS gives a speed of 215 knots for the circling area. (Jepp Text pg. 233 Table I-4-7-2) However, with that speed and timing based on 1,000ft AAL circle to land, you would end up approximately 2.7nm from the threshold.* Plus a turn inbound would still give you a margin on the 4.2nm. And that's at 215 knots! The normal reality would be closer to approximately 160 knots or so.

So my question is do other companies stick to something like 3 seconds per 100ft AAL? And if so why? Is there a EASA regulation there or is it up to the operator? Why not give a little bit more margin to create an easier final descent path? In practise, the AP is engaged and the aircraft is in level flight and well below the 3 degree path to land(being level downind). If we extended downwind just a little bit further then the final turn could be divide into more distinct parts 1) use the AP to establish on the centerline 2) disconnect and fly the descent manually. As opposed to the current procedure which is to do both at the same time. And give little time for a correction.

(Bearing in mind the responses that we should be able to do it all manually anyway etc etc, this is a particularly specific question about why the timing is the way it is)
*based on being 2nm distant from the threshold once abeam and a GS of 215kts for 30 seconds.

Thanks for any and all helpful replies.
Screwballs is offline  
Old 6th Dec 2013, 08:27
  #2 (permalink)  
 
Join Date: Mar 2012
Location: Dark Side of the Moon
Posts: 769
Our company used 20 seconds per 500ft AAL. So we would go downwind for 40 seconds at 1000' assuming nil wind. That would be at Flap 3, approx 140 kts (A320). Would always have plenty of room and be well inside the 4.2nm circling area. 30 seconds downwind does seem to be cutting it a little tight unless you are going really fast, that would seem pointless though as why not be configured early.
Ollie Onion is offline  
Old 6th Dec 2013, 08:39
  #3 (permalink)  
Thread Starter
 
Join Date: Feb 2004
Location: -
Posts: 206
Thanks for that, 40 seconds is a 33% increase on us and we do the same as you 319/320 F3, gear down approx 140knots turning base!
Screwballs is offline  
Old 6th Dec 2013, 08:46
  #4 (permalink)  

Aviator
 
Join Date: May 2001
Location: Norveg
Posts: 482
Circling is a visual manoeuvre. Why would you need to use a stopwatch? Because management does not trust you. And then they have to come up with some clever way of formalising and regulating your work. That's why the timing is the way it is ;-) Stopwatch circling is Taylorism defined.
Crossunder is offline  
Old 6th Dec 2013, 09:02
  #5 (permalink)  
Thread Starter
 
Join Date: Feb 2004
Location: -
Posts: 206
Well at least I've learned something from you - "Taylorism"!

How do you circle?
Screwballs is offline  
Old 6th Dec 2013, 09:31
  #6 (permalink)  
 
Join Date: Jul 2001
Location: East of West and North of South
Posts: 549
It doesn't have to do with protected area, but the ability to keep the runway in sight. Min meteorological visibility for cat C aircraft is 2400 meters.

With 3 sec pr 100 feet, you are quickly at the limit, as can be seen from the example below:

Downwind:

If going 180 knots ground speed, that is 3 nm pr min.

Min circling alt is 600 feet = 18 secs

18/60 sec x 3 nm/min = 0.9 nm = 1666 m

Turn radium (30 deg bank):

r = V^2 / G x Tan AoB

If V = 180 knots = 5556 m/s
g = 9.80665
Tan 30 deg = 0,577

= 981 m

Max distance from runway:
1666 + 981 = 2647

So you have to go slower that 180 knots ground speed or increase your minima respectively.
cosmo kramer is offline  
Old 6th Dec 2013, 09:37
  #7 (permalink)  
 
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 4,510
Circling is a visual manoeuvre. Why would you need to use a stopwatch? Because management does not trust you. And then they have to come up with some clever way of formalising and regulating your work. That's why the timing is the way it is ;-) Stopwatch circling is Taylorism defined.



B737. Average circle ground speed F15 is in the order of 160kts. The downwind timing is adjusted for tail winds. I find 3sec/1000' works out fine, in the sim. Considering the allowed visibility, 2400m, for CAT C a/c, and considering a foggy night, rain, low cloud etc. etc. it is wise not to venture to far away from the runway. It would be easy to stray outside the visible segment. 4.2nm = >6000m. The required vis is not related to the circling height, unlike DA/VIS on a straight in approach. True, it is a visual manoeuvre, but it is also a combination of 'dead-reckoning'. At low level in marginal conditions it is a good confidence to have a method, backed up by Mk.1 eyeball, that puts you in the right place on base leg to make a stabilised finals.
Imagine you were flying on the outside of the circuit at 500'. i.e. a right hand circuit from the left seat. The cross-wind leg is flown on timing to give you the correct spacing. You will likely be blind to the runway. Turning downwind you acquire it again. If the timing has been correct you should be spaced correctly. A pure visual judgement/perspective at 500' is not easy as it is uncommon. Passing the threshold you will once again be blind to runway. Are you suggesting that the low experience F/O doing this for their first time visually navigates you round a low level circuit? Not for me, thank you. I've experienced a dead-reckoning system hat works and I'll back it up with Mk.1 eyeball.
Remember this manoeuvre/procedure needs to work in manual flight as well as autopilot.
I once did some sim checks on F/O's from a 'gone bust' Mediterranean airline. Perhaps they were used to good weather, perhaps they had not done circling; either way they did not have a procedure. I gave them a circle at 900' at a major flat ground airfield, in 8km vis. They became completely lost downwind, starting turning searching for the runway, descended and would have crashed. They had no idea or structure of how to fly this manoeuvre. It is true that the numbers game does work for those who have nothing else.
It was proven to me at night in a caribbean island B767. Minimal lighting, no DME, no direct approach aid. It worked in real life too.
RAT 5 is offline  
Old 6th Dec 2013, 10:07
  #8 (permalink)  
Thread Starter
 
Join Date: Feb 2004
Location: -
Posts: 206
Thanks for the info.

Cosmo, the circling is based on an Angle of Bank of 20 degrees. Ref Jepp Text pg. 33. Plus I think you've made an error in the calculation, you used thousands of meters per minute instead of meters per second. I get a radius of 1,522m at 180knts/30 Aob.

So you think it's more to do with keeping the runway in sight? Fair enough, do you have a reference to where that might be specified?

If you had to circle on a day with a low cloud base but great visibility, wouldn't it make sense to extend downwind a bit to give yourself more space?
Screwballs is offline  
Old 6th Dec 2013, 10:36
  #9 (permalink)  
 
Join Date: Jan 2000
Location: FL410
Posts: 832
3x AAL' works great, correct for wind though e.g. +/- 1 second for HW/TW.

Be careful your chart shows circling minima for JAR OPS or Standard, not TERPS as these are less as our brethren in US will acknowledge.

This is why using the JAR OPS the circling manoeuvre is at a higher speed for the same category of aircraft as in the FAA. You will find when using TERPS charts to stay within its protected area you need to fly fully configured, whereas in JAR OPS charts we can fly gear-down on downwind leg and configure final landing flap in base turn.
Skyjob is offline  
Old 6th Dec 2013, 11:27
  #10 (permalink)  
 
Join Date: May 2001
Location: A few degrees South
Posts: 813
My company interprets the B737 FCTM circling procedure, where it states:"do not decend below MDH untill intercepting the visual approach path" as maintain MDH until in Final, lined up with the runway. Try to do this with 2400 meters visibility.
latetonite is offline  
Old 6th Dec 2013, 11:28
  #11 (permalink)  
 
Join Date: Aug 2012
Location: FL390
Posts: 148
3 seconds per 100 AAL with a large European 737 operator too. Corrected for tail or headwind by 1 second per kt. We disconnect the AP once on the PAPIs so one may or may not (more likely) be on the extended centreline at that stage.
737aviator is offline  
Old 6th Dec 2013, 11:43
  #12 (permalink)  
 
Join Date: Jul 2001
Location: East of West and North of South
Posts: 549
Screwballs,
I don't have Jeppesen available. In what context is 20 degs mentioned? One thing is what is used for procedure calculation, another thing is what you actually fly.

My calculation was meant as a practical example, and for sure I am using 30 degs AoB when needing to do a tight turn. Of course you are right, I took feet pr. min and not pr. second. Your calculation of approx 1500 meter for the radius is correct. Which just goes to show that it is not really possible to fly a circling in min visibility, especially if the MDH is higher than 600 and at high field elevation (higher TAS and hence GS). This emphasizes the need not to extent the downwind further than absolutely necessary.

My company recognized this problem by increasing our circling minima above the EU-OPS to 3000 meter met vis. It is still very tight at some fields, with MDA of 1100 feet, even if flying in landing configuration:

150 knot GS, 1100 feet for 33 seconds = 2546 meter
150 knot GS = 77 m/s, 30 deg AoB, radius = 1051 meter

150 knots GS is not unrealistically high for a 737-800, even in landing config flaps 40, if full of pax.

Max distance 3597 meter. BUT keep in mind that ICAO doesn't require you to keep the runway itself in sight, but runway environment. That includes approach lights system or "or other markings identifiable with the runway". So technically it is possible, but tight... I would probably consider a diversion, depending on other weather factors (is it just mist and steady wind.. or heavy rain and gusty/turbulent), and I am quite sure no one would blame me afterwards.

As for in better conditions, I don't see a reason to extend the downwind, if you start the descent when beginning base turn, you have (in the above example) 2546 meter + 1/2 circumference to descent 1100 feet.

1/2 C = (pi x 2 x r) / 2 = 3300 meter

5846 meter = 3.15 nm ~ 3 degs path. Also your downwind will already be extended further as you won't fly in landing config, hence your GS will be higher. Also you will have headwind (otherwise, why did you circle?). Plus you can adjust you AoB/fly the base a little further from the runway to give you more space..

There are other good reasons not to extend, depending on the airport. Izmir, LTBJ, runway 34R circle to land 16L is a good example of that. Yes they do that at times in good weather conditions despite ILS16L available. If you extent your downwind you end up over a 1240 feet high hill (circling altitude 1500 feet).Being over it and unable to see it is more uncomfortable than starting the turn just prior, as it would work with 33 seconds (MDH 1090 feet).

Like fighter pilots say (I was never one, but they have a lot of good sayings ), "fight like you trained, and train like you fight".
cosmo kramer is offline  
Old 6th Dec 2013, 12:01
  #13 (permalink)  
 
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 4,510
My company interprets the B737 FCTM circling procedure, where it states:"do not decend below MDH untill intercepting the visual approach path" as maintain MDH until in Final, lined up with the runway. Try to do this with 2400 meters visibility.

The visual approach descent segment used to be +/- 30 of C.L. On a circle procedure using 3 x AGL/000's you should roll into the 60-30 degree cone with 2R 2W. You need to descend. If you stay level until on C.L. surely you'll end up 4W and diving. Not good if at only 500' to start with. If within the segment and visual why can't you descend to attack/maintain PAPI's to assure the stable landing gate; or would they rather you risk being unstable and landing long?
RAT 5 is offline  
Old 6th Dec 2013, 12:08
  #14 (permalink)  
 
Join Date: May 2001
Location: A few degrees South
Posts: 813
To Rat5: I am trying to shoot down the argument as well, but lack the bullets. Where can I find this 30 degree description?
latetonite is offline  
Old 6th Dec 2013, 12:33
  #15 (permalink)  
Thread Starter
 
Join Date: Feb 2004
Location: -
Posts: 206
All good stuff, thanks. It is a rather theoretical question! But I like getting into the gritty details so the bigger details make more sense.
Screwballs is offline  
Old 6th Dec 2013, 12:44
  #16 (permalink)  
 
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 4,510
ref: +/- 30 degrees. Years ago in the days of PANS Ops introduction I was told that a circling approach was anywhere the final approach was outside 30 degrees of the RW C.L. Thus it was required to manoeuvre more than 30 degrees on short finals. I can't give a link.
How do your guys advise to fly a visual circuit? That should be a descending base leg onto finals for a CDA. A circling base leg onto finals is also a visual manoeuvre.
RAT 5 is offline  
Old 6th Dec 2013, 13:18
  #17 (permalink)  
 
Join Date: Jul 2001
Location: East of West and North of South
Posts: 549
Doc 8168:

When the OCA/H is established, an MDA/H is also specified to allow for operational considerations. Descent below MDA/H should not be made until:

a) visual reference has been established and can be maintained;
b) the pilot has the landing threshold in sight; and
c) the required obstacle clearance can be maintained and the aircraft is in a position to carry out a landing.

No mention of 30 degs or being established on final..
cosmo kramer is offline  
Old 6th Dec 2013, 14:29
  #18 (permalink)  
 
Join Date: Mar 2000
Location: Sunrise Senior Living
Posts: 1,294
You should be d/w at F speed (140 to 145) with F3 assuming 2 engs.
Diameter of turn at that TAS (no crosswind) is about 1.5nm so stay close.
3xht in secs corrected from abeam. Always go a little further if you can (5secs) then spin the TK Selector onto the RW TK, leaving the AP on. Watch the X-TK error counting down. Half way round, you should be only .7 or .8 cross TK. Now look out for the PAPIs. When you see 3 reds, AP off, FDs off, FPV to minus 3 degrees, flap full and keep an eye on the magenta donut if FPL is sequenced! Landing Checklist. Cleared to land? Et voila!!
mcdhu is online now  
Old 6th Dec 2013, 19:58
  #19 (permalink)  
 
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 4,510
"woods for the trees." KISS
RAT 5 is offline  
Old 6th Dec 2013, 23:23
  #20 (permalink)  
 
Join Date: Apr 2005
Location: Southeast USA
Posts: 802
I posted a set of comments, not long ago, on what I believe I’m seeing more regularly in this industry … that being the development of, and the subsequent dependence on, a “set of numbers” that are presumed to be the “answer” to the problem or the situation under scrutiny. Unfortunately, from what I’ve seen, this practice has become a rather routine goal of an increasing number of aviators – the practice likely initiated when each person was a “new hire” … ostensibly generated either by that person, or other persons, to provide an outcome of the specified task, under the specified circumstances, using the specific set of numbers, to allow the appearance of an adequate piloting performance.

I even described several “number set” discussions …
Originally Posted by AirRabbit
“…for tasks such as … “what engine parameters should I set for a heavy weight landing in an XXX airplane type?” or “what rate of descent should I hold during a zero flap approach for an XXX airplane type?” or any of the multitude of other similar “examination crutches.”
The line of thought represented in this particular thread is yet another example of seeking and providing information regarding the accomplishment of a very specific flight task - here, the completion of a circle-to-land – where simply “plugging in the provided numbers” will provide an “adequate” result. The fact that a "circle-to-land" is a visual maneuver appears to be completely disregarded and replaced with a dependence on altitude and stop-watch timing to determine when to turn to land. It's a VISUAL maneuver. It has nothing to do with blindingly flying until a determined number of seconds has ticked by - and then doing something else - likely just as questionable. The reason such a task is included is to allow a pilot to fly an instrument approach procedure to get below a cloud deck or within visual range of the airport and from that point, visually maneuver the airplane to the runway on which the pilot was cleared to land. Nothing more. Nothing less. Deliberately ignoring the concept of keeping the landing runway in sight while maneuvering to land completely ignores the concept on which the procedure was developed - and potentially sets up a skills-deficient pilot for almost anything less pleasant than landing on the runway originally intended.

If I were ever to plead with anyone about flying an airplane – particularly an airplane with innocent passengers aboard – where their presence is only due to the fact that they “trusted” in the ability, knowledge, and professionalism” of the pilot – this is where and what I would plead ... Please … evaluate the reasons you are asking for such information … review the mechanics required to perform the task in question … talk with a flight instructor you trust … practice the mechanics involved in completing the task in question … ask your instructor to critique your performance and offer recommendations for improvement … and then repeat that sequence until you and your instructor agree that you have learned how to perform the task.

There is nothing wrong with breaking down any flight task into the scientific and mathematic parameters that are involved … however, your reliance on being able to repeat any such sequence of parameters may well work only under circumstances essentially equal to the circumstances that existed for the task associated with the particular flight task on which the analysis was accomplished. Being a pilot is highly individual ... and is dependent upon being able to deal with the circumstances that exist at each individual point in time and space, which you, as a pilot, are expected to perform. It’s analogous to learning how to write by copying and committing to memory (both mental memory and muscle memory) very specific sentences, paragraphs, or books. Then, when you are inevitably asked to write the answer to “how do you feel?” you might well find yourself being quite ill-prepared to write an answer to that perplexing question. However, if you were to have learned how to read, write, spell, develop sentences, understand punctuation, and the like … you might be able to write an answer to such a question without having to be overly concerned about the concepts of verbs, adverbs, connectors, personal pronouns, and adjectives … like, “I am feeling pretty darn well, thank you.”

It may take some innovative thought processes on your part, and certainly a lot of effort and a lot of practice, but you will find it supremely beneficial to learn to fly rather than learning to apply a canned sequence of numbers to any specific circumstance you might meet in your aviation career.
AirRabbit is offline  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.