Circling Calculations

[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]

aviate

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]

Originally Posted by Capn Bloggs

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]

Circling Approach Awareness

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.

[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.