Circling Calculations

[Dadanawa]

Trying to create a workable spreadsheet for circling calculations.

So far this is what I've come up with.

Entries in yellow cells, calculations in blue cells.

Comments, questions, and suggestions are welcome.


http://i779.photobucket.com/albums/yy71/Dadanawa/image_zps52ciyw2d.jpeg (http://s779.photobucket.com/user/Dadanawa/media/image_zps52ciyw2d.jpeg.html)

[Checkboard]

Why?


... and you're too close to the runway. Should be about 1.5 to 1.7 nm abeam.

[Dadanawa]

Distance from runway depends on turn-radius for given speed. As speed increases, turn-radius increases, and distance from runnway increases.

Why ?

Takes the guesswork out during a procdure that is not commonly flown.

[Goldenrivett]

Hi Dadanawa,

You did bother to draw this circuit out before posting your maths - didn't you?

If the downwind heading is 281 degs and the wind is from 269 degs at 10 kts, why are you bothering to circle to land with a 10 kt tailwind on finals?

If the circling direction is Left hand circuit (/L) why are you turning Left (253)? You would then surely be turning Right to turn onto finals. (What we used to call a Right Hand Circuit).

If I was flying at 1500 ft agl I would fly from abeam THR to base turn for 45 secs in still air. Since I have a 10 kt headwind flying downwind, then I'd turn at 55 secs (not at 33).

I think you'll find you need a mental picture to fly circuits - not a list of numbers.

[vilas]

There is some confusion. I think you mean left break and not circle left? Why 30 degrees offset? should be 45 degrees and 30 seconds.

[donpizmeov]

Circling is a visual procedure. More time with eyes outside and less looking at an app might be a step in the right direction.

[Dadanawa]

Yes Vilas,


What I mean is a left turn to right downwind.


And yes, in this particular case there is a tailwind. (Just entered arbitrary figures)


Separate sheet for 45 degree break.


I'd say figures can be entered quickly once you get the ATIS. Might take 20 seconds.

[galaxy flyer]

If you can't make this work in your head and translate it into a flight path in the plane, you need to reconsider your career choice. How are you going to use this spreadsheet on a rainy afternoon just below the clouds in a jet?

GF

[vilas]

At 1500ft do a normal circuit as in most aircrafts done at 2.5 nm downwind displacement. Japs do at 2nm. You don't need a spread sheet.

[B737900er]

Icao/Pans -ops we fly 4.2nm for 180kts or 5.28 at 205 knots.

[Matey]

Reminds me of the situation in my company a while back when the PM noticed PF rummaging in his flight bag when downwind on a visual approach in manual flight with no hands on the controls. When challenged he stated he was looking for his calculator to work out timing from abeam the threshold before turning finals!

[khorton]

In the real world, the wind changes as the altitude changes when descending. These changes are sometimes quite significant. I find it works best to look out the window, and vary the bank angle and descent rate as required so the aircraft ends up where I want on short final.

[compressor stall]

The primary instrument in a visual approach is the window.

[harpf]

1) Doing a bit of math my help the beginner to understand the limitations and trade space available to when flying the maneuver. The FAA has taken a crack at this for no wind with for us when setting up the A-E category minimums. These have recently been revised as they were a bit optimistic about what could be accomplished safely.


2) As a GA pilot who fly's a bit of IFR into small airport, I have performed as many real (IFR and not training) circle to land as I have real ILS approaches.

[Capt Fathom]

Hill? What hill?

[vilas]

B737900er
Icao/Pans -ops we fly 4.2nm for 180kts or 5.28 at 205 knots.
Really? I think you have misunderstood the PANS OPS. It gives the limit of visual manoeuvring area available. Why would you place yourself at the edge of the area? Even if you did turn downwind at 205kts it will place you 2.34nm on downwind.

[B737900er]

Sorry, I didnt make myself clear there what I meant is those are the limits we fly to. As you said rightly said, you would be well within those limits.

Timing 3seconds per 100' Agl +\- wind

[avoka]

There is not +\- wind correction for circling approach in according to Airbus documents.
There was the thread here regarding this correction
Safe flights

[Goldenrivett]

There is not +\- wind correction for circling approach in according to Airbus documents.
Can somebody please explain how the physics of ground speed changes if the only difference is that some aircraft now have a computer between the pilot and the control surfaces.

[vilas]

avoka
There is no such document by airbus. You can read your FCOM the timing is very much there.Also read the thread again fully.

[Stone_cold]

I am curious to know where in the FCOM or FCTM it states that there is a wind correction for circling . As far as I see there is an "approximate" 3s/100' because it is a visual manoeuvre . That seems to be the only timing mentioned on downwind .

[Capn Bloggs]

Timing 3seconds per 100' Agl +\- wind
I reckon this is nonense and have done for years. What does it matter how high you are going abeam the threshold? The critical issue is going Downwind the correct distance so you will roll out of final by 400ft (or higher if you have to be stable higher up). By all means start descending passing abeam but the turn must occur at the same point over the ground. Headwind/tailwind on Downind? Adjust turn point by 1/2 second per knot of H/T.

[RAT 5]

Bloggs: Your 'circling' technique is not that approved by Pans Ops if circling at minima. Yours might work if flying a visual circuit above minima, but not on a manoeuvre conducted with cloud base sniffing minima.

[avoka]

Hi Vilas
I did check fcom and fctm during reading that thread and was so surprised that these docs had not recommended to do wind correction.Anyway it's good method to check distanse from active threshold ☝ �� �� and I think it's not so critical to have some extra distance due to tailwind on the base turn!
Safe flights

[vilas]

I am talking about end of down wind time. Blogs, your procedure seems to be different. Airbus wants you to time from abeam threshold as corrected for wind and start a level turn for finals, when you are about 90 degrees to the runway if correctly vertically positioned only then commence final descent. Purpose of timing is to place you at the same spot on ground for final turn. Basically a visual manoeuvre timing is for guidance. It has to be altered as required to remain visual and keep runway in sight.

[Capn Bloggs]

I am talking about end of down wind time. Blogs, your procedure seems to be different. Airbus wants you to time from abeam threshold as corrected for wind and start a level turn for finals, when you are about 90 degrees to the runway if correctly vertically positioned only then commence final descent. Purpose of timing is to place you at the same spot on ground for final turn. Basically a visual manoeuvre timing is for guidance. It has to be altered as required to remain visual and keep runway in sight.
Precisely as I said, Vilas. You can be at an MDA of 1500ft or 500ft, or have gone down to 400ft (PANs ops Cat C terrain clearance). It doesn't matter. Turn on time, corrected for wind. Use a Fix if you need a crutch. The crunch is, as you mention, keeping Visual with the threshold or "runway environment" on the latter part of Downwind. Very difficult if you want to roll out on Final at 1.5nm/500ft ("Stable"). And you will almost certainly exceed the circling min vis on the first part of the base turn. Never see the runway then...

And Yes, you do commence final descent only when intercepting the "normal" 3° path. At 500ft, that means a level turn all the way round.

[avoka]

Vilas
Let's think about the weather conditions during circling.It is not visual maneuver when good vis and clouds so high.It is option for pilot when weather conditions are lower than for visual pattern,but tail wind component little bit greater then wind for straight in approach.On default You have 10 kts min or greater tailwind at point abeam threshold,ergo -1 sec,but I think that it's not so bad to just keep in mind it,but to perform base turn in according to fctm recommendation and You are at point with extra distance from point in calm conditions-You just have to decrease Your v/s , the same time pay more attention to circling radius for cat C,D planes
Safe flights

[vilas]

avoka
When you turn 45 degrees and fly for 30seconds that also needs to be adjusted if winds are strong. That takes care of circling radius. Below from airbus document:(Not for those who consider everything other than what they know as abstract document)


5.4. Timing for Circling:


The timing Airbus recommends is 30 seconds from wingslevel, adjusted for strong Head or Tail wind, by reference to the ND windindicator. However, this is a visual exercise: Timings are approximate only.


Blogs, I have to disagree with you about going down to 400ft. It is not a question of terrain clearance but obeying the circling minima. You cannot descend below minima to fly level. You can only descend below minima during the final turn

[Capn Bloggs]

The timing Airbus recommends is 30 seconds from wingslevel
Vilas, is that from abeam the threshold? Sorry, not familiar with Airbus circling procedure.

You cannot descend below minima to fly level.
Regulator's rules: we can descend to the minimum terrain clearance altitude in daylight.

[vilas]

When you break from the NPA at circling minima and turn 45 degrees either left or right then once the wings are level fly 30 seconds from wings level adjusted for wind for suitable displacement on downwind.

[vilas]

Bloggs
Do you operate to TERPS or PANS OPS?
PANS OPS says
Descent below MDA/H should not be made until: (1). Visual reference has been established and maintained. (2). The pilot has landing threshold in sight. (3). The required obstacle clearance can be maintained and the aircraft is in a position to carry out the landing.
Can the last condition be assured on downwind?

[avoka]

Vilas
agree-RECOMMENDS!!!! just recommended!!!
There are not such recommendations in documents,just magazine
Safe flights

[Capn Bloggs]

Vilas, PANS Ops. As I said, our CAA allows descent below MDA to terrain clearance in daylight prior to final descent.

Still confused about how far Downwind Airbus says. You could turn off the 45° degrees anywhere. But what defines the Base Turn point? 30" from abeam the threshold?

[Stone_cold]

Bloggs : approximately 45" to the landing threshold .

Vilas : could you say where it states that the downwind timing is adjusted for wind from the abeam point?

[Checkboard]

Capn Bloggs is obviously in Australia, where you can descend to 400' obstacle clearance in daytime (but must maintain MDA until you can make a constant descent to land at night).

In Australia it is also typical for the final approach for an NPA to not be runway aligned - it may approach the runway at any angle.

Bloggs, the Europeans typically only consider circling from a runway aligned approach - with the circle to the opposite direction runway - so the whole 45º for 30 seconds bit is how they obtain their downwind spacing. Not a good procedure, but Europeans never circle as a rule (so they are always nervous about it), which is why the OP wants an aid for it rather than looking out of the window.

[vilas]

Stone_cold
There was a instructor seminar held by airbus in 2012 which I myself attended in which one of the topic discussed was circling approach. What I quoted is from that. Since it is a mechanics of approach and a technique I consider it as valid. Otherwise even FCTM has no legal validity like FCOM. Since lateral downwind spacing is determined by ground speed in strong crosswind the head/tail component needs to be catered for. As stated timings are for guidance only.

[vilas]

Blogs
If you descend to terrain clearance 400ft on downwind do you consider approach stabilised on downwind? What is the stabilised approach requirement for your regulator?

[Stone_cold]

Vilas : I am not questioning the downwind spacing of 45° / 30 secs. I was asking about +/- corrections to determine the base turn , i.e. timing from the abeam position ( 3 secs/100' ) .

[Capn Bloggs]

If you descend to terrain clearance 400ft on downwind do you consider approach stabilised on downwind?
Not until steady on final commencing descent on the PAPI. We were approved for 400ft, then it changed to 500ft to "fit in" with everybody else, and now visual circling is not permitted as we have straight-in RNAVs everywhere. I note Airbus comments about using a 400ft stable height for circling approaches in it's Stabilised Approach note (http://www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-APPR-SEQ01.pdf).

Back to the OP's issue, while this is supposed to be a purely visual manoeuvre, I think there is a case for using "the system" to help. I'm definitely not suggesting a building a full LNAV/VNAV min wx circuit, but using Fixes makes life easier, with no need for 45/30. My preference is to place a fix at the end of the Downwind leg ie at the Base turn point, then put a "radial" line back along the Downwind leg. When you get Visual, you then simply fly over to the line in TRK, follow it to the fix and turn Base. Having an app that would calculate that Fix point (taking into account spacing out from the runway/crosswind effect and distance/head/tailwind) would be helpful. The stopwatch would be used as a backup.

The Fix position would be based on the threshold waypoint. You could input the runway QFU, the wind velocity, the bank on Base and the speed, and it'd spit out the location of the base turn point WRT to landing threshold.

For normal circuits, I just use 40° off at 3.4nm.

[vilas]

Flying circling approach in nav mode is not a good idea and is forbidden in airbus after Air blue crash in Islamabad. Even in India circling approach is forbidden. Why a 3.4nm circuit isn't it too wide?

[vilas]

Stone_cold
I thought you yourself stated As far as I see there is an "approximate" 3s/100' because it is a visual manoeuvre . That seems to be the only timing mentioned on downwind .
The reference is the diagram on page stated below.
PRO-NOR-SOP-18-C P 15/18

[Capn Bloggs]

Agreed: I'm not suggesting flying it in NAV. 3.4nm is the distance to the Fix: equates to 2nm spacing on DW and rolling out on final around 2nm/600ft.

[Stone_cold]

Vilas , maybe I am not being clear , you stated : I am talking about end of down wind time. Blogs, your procedure seems to be different. Airbus wants you to time from abeam threshold as corrected for wind and start a level turn for finals, .

What is your reference for " as corrected for wind " ? The 3sec/100' has no wind coresction .

[vilas]

Stone_cold
You are correct for circling approach there is no correction for wind end of downwind in FCOM. I mixed up with normal circuit because the discussion also stated somewhere the circuit height as 1500ft which is normal circuit height which is corrected for wind abeam landing threshold. The airbus article says only about turning downwind 30 seconds corrected for wind and abeam landing threshold as 3sec/100ft as visual exercise, timings are appx. only and to use ND (for correct placement).

[autoflight]

On 15th April 2002, Air China B767 CFIT during circling at Gimae Busan (Pusan) South Korea. Weather was low cloud, 215/17, reduced vis. ILS rwy 36 with RH circle to rwy 18.

47 K tailwind at 2200 ft with assumed tailwind on downwind
Close high terrain north of airfield which was not visible
Circling minima 1100 ft, but crew used 700 ft.
Reduced perspective of the runway from LH seat in right turn
Captain had operated to Gimae 5 previous times, but always straight in approaches.
Air China did not consider this to be a special airport
Crew expected straight in, but there was a runway change due doiwnwind on rwy 36

Note that the circling approach procedure has since been modified with stobe lights for the base turn.

My recommendation would be to study the detail of accidents such as this in preference to spending too much time on an app. A good account can be found at http://flightsafety.org/ap/ap_dec05.pdf

[galaxy flyer]

Busan approaches were also designed to TERPS, not PANS-OPS--significant difference in circling areas.

GF

[autoflight]

TERPS is mentioned in the link

[Capn Bloggs]

significant difference in circling areas.
You're not wrong. The old terps was just ridiculous for circling. Good for a C150, not a jet (although 411A argued til he was blue in the face is was no problem). The new rules aren't much better, methinks.

That prang was a good example of where, if you are forced to do a circle, technology (eg use of Fixes on the ND) could greatly assist SA.

[vilas]

You're not wrong. The old terps was just ridiculous for circling. Good for a C150, not a jet (although 411A argued til he was blue in the face is was no problem). The new rules aren't much better, methinks.

That prang was a good example of where, if you are forced to do a circle, technology (eg use of Fixes on the ND) could greatly assist SA.

If you want to use technology, in airbus you can use radial in function to the runway threshold and it gives you glide slope guidance from yo yo. But again it's visual manoeuvre.

[Dadanawa]

The discussion and posts have been interesting.
As I continue to continue to work on the spreadsheet, I've made some adjustments.
It now gives me the bearing and distance to enter three fixes on the downwind leg (FOR AWARENESS ONLY.)

Fix 1: Calculated distance abeam RWY threshold.
Fix 2: Distance from abeam RWY threshold to base turn.
Fix 3: Distance from abeam RWY threshold to limit of PANSOPS protected area.

For 737NG FMS, these fixes can be entered using the RWY fix in the LEGS page.

To do this, a new RWY fix must be created -0.1 back from the RWY fix. e.g. RW05/-0.1. Bearing and distance can then be made from this new fix. The normal RWY fix does not accept bearing and distance.

Comments, questions, and suggestions are welcome.

http://i779.photobucket.com/albums/yy71/Dadanawa/image_zpspttfj11w.png (http://s779.photobucket.com/user/Dadanawa/media/image_zpspttfj11w.png.html)

http://i779.photobucket.com/albums/yy71/Dadanawa/image_zpsliqeaa4s.jpeg (http://s779.photobucket.com/user/Dadanawa/media/image_zpsliqeaa4s.jpeg.html)

[Capn Bloggs]

I haven't checked your numbers but... the base turn time of 16" is too close. That would roll you out on Final at 200ft-ish. Vilas says Airbus base turn is at 30"... I think even that's a tad close.

For my understanding, what runway are you landing on here?

[Dadanawa]

I've used a timing based on the height to lose from MDA to threshold at 318' per nautical mile at the current GS on downwind. Not adjusted for the change in GS on final.
Runway in spreadsheet is LTFJ. Runway in photo is LTFE. The downwind spacing seems okay.

[Capn Bloggs]

You need to work backwards from when you have to be Stable ie on-slope (3°) at 500(?)ft. That will define where you roll out of the base turn, then work back to the base turn start point, then the groundspeed on Downwind will define how long you go Downwind for. As mentioned previously, this may mean you fly a level Base turn initially, then start the final descent when intercepting the 3° path, hopefully to roll out at 500ft (or whatever your Stable rule is), on slope. For example, if circling at 1000ft, start down half way round the turn. If circling at 600ft, start as you approach Final.

[Dadanawa]

Yes this makes sense, you don't want to be turning onto final at very low altitudes. I'll rework the calculations based on a 3 degree path from the landing runway. Probably I should use 600 feet to be stable as this approximates lowest OCH above aerodrome elevation.


Airport in spreadsheet is LTAF.

[RAT 5]

Coupling this topic to those about the dilution of manual flying skills and flight path visual judgement, I hear there are airlines who have grave doubt about the capabilities of even captains to conduct visual finals to runways without GP guidance. To that effect it is only allowed if there is a VNAV constructed path from a minimum 4nm point to the runway. Further, some use airports where a circuit is required to the non-instrument landing runway with PAPI's unreliable or non-existent. A circuit is constructed with FMC WPT's and full LNAV/VNAV guidance to bring you onto a visual finals 'in the slot'. A classic 'children of the magenta line' approach to a circuit arrival. Sad days.
One day there will be an advert for 'Airline Dodo's wanted'.

[Goldenrivett]

A classic 'children of the magenta line' approach to a circuit arrival. Sad days.

Hi RAT 5, I agree.

It is sad for those of us who flew before the invention of such aids like FMGCs and pictures on Nav Displays with actual wind and ground speed shown but it would be mad to dismiss them, because using such aids enhance our SA.

However I still believe it should be a basic skills requirement to be able to judge a visual circuit using the view out of the window, backed up with the scale markings on the NAV Rose Display if available and the wind vector information provided.

Making up spread sheets is only inviting other errors in the sheet and / or typos.
Always KISS.

[piratepete]

An APP FFS! I was lucky enough to operate in a 737-200 around the south pacific for many years before moving up to LNAV/VNAV flying on big jets, and the 3 seconds per 100 feet above airport elevation after passing the threshold downwind worked every time in the most horrible weather conditions.A small nod to wind effect was often made but the basics were always the same.Stay level until you were more or less heading to the runway then down you go at a nominal 700 fpm, many times with no PAPI etc.Obviously this was generally with sea level ports with not much terrain about, so this is problematic at say BUSAN for example where special procedures are needed to be trained/adhered to.TERPS or PANS OPS not really relevant.What ever has happened to this type of skill............Pete.

[compressor stall]

How can you calculate your base turn without inputs for your angle of bank and your speed. This will affect your radius and thus your distance flown. Your ROD will be equally affected. It is not a simple task. And throw wind into the mix.

Many years ago I had to calculate the turning radii with different winds to intercept a lat/lon at a time to the second. Even in level flight, it is complex with many variables, and that was clean, level without changing config or speed...

As I said above, manoeuvre into position laterally on downwind, then turn in looking out the window. Reduce or increase the AoB depending on how tight you are. Pull / push sidestick/yoke/throttle as appropriate if you are low or high.

It's a visual manoeuvre, using your eyes and judgement.

If you can't, there's an app for that. It's called the ILS or RNP AR. The button's on the FCU.

[Capn Bloggs]

I think you guys are being a bit harsh. Precisely what Dadanawa is doing will equip him well for visual circling. CS, you had better work out your expected turn radius beforehand: too close and you could well stall the thing. One can do quite a lot of preparation before doing a base turn, so that the event itself is easy, despite ugly weather. Simply saying "pull/Push" if you don't know what you're doing is going to end in tears.

I will repeat my rider: this is not for LNAV/VNAV use. But arming oneself beforehand is good value IMO. PPPPPP.

[compressor stall]

An academic interest of the maths and the "perfect" circuit is one thing for a spreadsheet.

Sure, use this information to understand where the FCTM/FCOM figures come from as a starting point but then you modify it by looking out the window.


BTW, the radius doesn't change if the downwind leg is in the same location each time.

[Uplinker]

People's minds work in different ways.

Some can do maths very easily and use that; others find it easier to fly visually by seat of the pants. I can do mental maths or I can fly, I can't always do both.

I did a similar thing to the OP in that during my ATPL training, I programmed a Psion (remember those?) to work out hold entry and headings etc, for me - given the wind. Of course just before a critical flying test, I dropped my Psion which jogged the batteries and my program was lost !! So I was back to mental maths and ready reckoning. (I passed the test by the way !!)

Nevertheless, I found that my hold program had been very useful to help me explore how things varied with wind, and by changing one parameter I could see how every aspect of the hold changed. Having done this and worked through many examples, I understood the dynamics and I didn't need my hold program again. Later, when I flew basic BAe146s, I got very good at flying holds on the heading bug, just using the seat of my pants. Thanks to the amount of traffic trying to get into Heathrow, I had lots of manual hold practice over Ockham !

So I don't think there is a problem with the OP working out the circling approach in this way. I don't think it means they are trying to fly the perfect circling approach, I think they are just working it out in their mind.

I sat down with a piece of paper and used my remembered school trigonometry one day to work out where the 3s per 100' would actually place me, geographically, relative to the runway. A useful exercise, since I now know roughly where to turn base using visual references without doing any maths as I fly, (and this automatically takes wind into account.)

Good luck D, but don't use your spreadsheet when flying. You will become unstuck one day if you do. Just use it to explore and understand the manoeuvre.

.

[autoflight]

Dadanawa, While studying scenarios, by all means look at those that you feel "fit" into the ordinary possibilities, but do not avoid the extraordinary situations. In very high winds, the base turn might need to be commenced prior to reaching abeam the threshold, in order to remain within the circling area during the turn onto final. Timing is irrelevant if compliance results in busting the circling area.
It is no comfort to your widow that remaining within the circling area meant flight through unacceptable weather events like a microburst.
So it is not just a computer app, but aggressive animal survival instincts that can sometimes count.

[Dadanawa]

Very thoughtful post. I'm working on the calculation for the point on the base leg turn to start descent. Calculated in time or bearing from threshold . Will keep you posted. I don't envisage ever using this down low. But it will help with getting the big picture.

[RAT 5]

How do you drive around an oval shaped roundabout to an exit you can't see? Don't try to calculate your route around L"Etoile in Paris wanting to take the 6th exit from your entry, where you start in the inside lane and need to drift to the outside one in time. After 3 revolutions in rush-hour traffic you throw away the TomTom and decide that dare & cunning works better.

[autoflight]

The complexity of circling can be found in the following links.
Circling Approach Survival Guide | BCA content from Aviation Week (http://aviationweek.com/bca/circling-approach-survival-guide)
Circling Approach Area (http://code7700.com/circling_approach_area.html)