Circle to Land

[Sebastian Maguire]

Circle to Land.

I would be grateful for a highly technical explanation on the subject. (assume that I already know the basics)

Some time back we flew into Carcassonne, France (LFMK, Salvaza) on good old Ryanair and I plucked up the courage to ask the Captain about his circle to land approach.
It was the usual Follow the ILS glideslopre down to runway 10 using v/s then break left at the circling minima (1500' w/o Local alt set) before completing the rest of the pattern to land on runway 28.

His explanation at the time was highly detailed as he refered to specific decent rates and speeds but I have unfortunately forgotten them.

Since that time, I have posed the question on many a forum, never to receive a satisfactory answer so I hope some people who have actually flown this approach may be able to assist.

Some replies have been of the "break off left and just keep eyeballing the runway as you pass the threshold bla bla bla" but what that Ryanair captain gave me was quit a technical view of it with all sorts of info.

The Fs2004 simulator using PMDG 737-800's with only one screen and "paralax" errors that prevent you from perfect visual judgement is quite tough to handle during this approach. It's perfecting the right time and distance to turn downwind then base then final at the same time as a smooth decent rate etc.

Some people have suggested that p/f's in the right seat who need the advantage of seeing out that right window and keeping the runway in sight, will get their captains to puch in Runway 28 in the Fmc so as to have the Magenta line arcing for a smooth turn to final. Others have disputed this.

I would be grateful for as many specifics as possible on how to master this approach technically as well as visually. Specifics that include the right time to turn on all phases of the approach, the right way to set up a smooth decent, the right speeds, flap settings and the right distances to keep in mind.

Anyone wanting to say "A visual approach is exactly that so forget about getting to technical" then i've heard it before. Anyone with a mathematical view that involves some interesting trigonometry would be welcome.

Thanks

Sebastian

[Ibanez]

Hi Sebastian,
I haven't flown the approach at LFMK, but here are some of the basics: Firstly, if you are going down the ILS, don't arm Approach mode - use V/S down to your MDA (set MDA rounded UP to the nearest hundred on the MCP). Configuration should be gear down, flaps 15 with speed brake armed.

At MDA, wait for ALT HOLD, set your missed approach altitude, select HDG SEL and offset track 45° L/R, depending on the plate. Keep this heading for 20 sec from wings level, then turn downwind. When abeam the landing threshold, start the clock. Fly outbound for 3 seconds per 100ft AGL (ie - if MDH is 800ft AGL, fly outbound for 24sec). Correct for wind by taking 1/2 the tailwind component and subtracting it from the 24sec (just go to progress page 2 and divide the TWC by 2).

Once time is up, request landing flap, match the speed, set RWY heading and use V/S to start a 300fpm descend, complete landing checklist. Use your position trend vector and what you see outside to judge the turn and adjust your bank angle with the bank angle selector accordingly. Intercept the normal visual glide path and disconnect the autopilot and autothrust. Verify your missed approach altitude is set and request for the flight directors to be recycled.

That's about it! No trig or geometry involved :ok:

[Gary Lager]

First of all, a circling approach IS a visual manouevre - whilst the minima for Cat C aircraft is fairly generous (2400m vis), I wouldn't fancy doing one in those conditions. If visual contact is lost at any point during circling a go-around must be flown.

As to actually flying the circling part - in a modern jet airliner like the B737 or A320 it is not sufficient to just 'eyeball' it- we need some numbers to help us manage the momentum and position of the aircraft in order to acheive a stabilised final approach to the landing runway.

So, in the 737 (my current type), to land on the runway reciprocal to the instrument approach:

Approach is flown to circling minima to the instrument runway - if an ILS approach, NOT using 'APP' as it is impossible to disengage after G/S capture without taking the A/P & FDs out. So HDG SEL and V/S, and level off at circling minima by pressing ALT HOLD at (approx) 10% of the vertical speed above the circling altitude.

This part of the approach is flown with Gear Down and Flaps 15 ~ approx 150kias. Autopilots in until the final turn.

Then a level segment is flown to 1/2nm from the threshold of the instrument runway, at the same time the MCP is reset for the missed approach altitude.

At 1/2nm from the threshold, we turn left or right (depending on airport restrictions eg terrain, ATC instructions and/or pilot preference) to give us an offset TRACK of 45 degrees (i.e. heading corrected for wind). Start the stopwatch.

After 45 sec (wind corrected, 1 sec per knot of head or tailwind) turn to track parallel to the runway - downwind to land.

Abeam the threshold re-start the clock.

After 10-15 sec (wind corrected):
Autopilots OFF
Flight Directors OFF
Flap 25, 140 KIAS

..and start a descending turn onto finals.

As we turn onto finals, select Flap 30/40 and the appropriate approach speed.

Aircraft should be stabilised (configuration, speed, rate of descent) by at least 300' above the landing threshold.

Land.

Of course, if the landing runway isn't 180 degrees out from the approach runway, things are a little different - but the objective is still to arrive downwind to the landing ruway at about 1 1/4nm spacing, at a typical circling minima of about 500-600' QFE.

Hope this helps, happy to expand on any terms you are unfamiliar with.

Profile for the A320 is very similar, but the automatics are slightly different.

Whoops! Ibanez beat me to it. He has some good gen in there which I'd forgotten, about adjusting the timings for variations in circling altitude. I don't fly circling approaches very often (thank God) so am a bit out of practice!

The above taken directly from our Company Ops Manual.

[Centaurus]

Ibanez. The published MDA for circling will normally assure you of legal obstacle clearance within a defined distance of the airport. Without knowing precisely which is the controlling obstacle you should not descend below the circling MDA (especially at night) until within the approach splay on the runway you are landing on.

Of course if you have the ground in sight along your intended flight path at all times and can ensure safe obstacle clearance (day or night) then descent is at your discretion.

But on a dark night where it may be impossible to see the terrain in front and below, you should not descend below the published MDA while on base leg. If there is a VASIS serving the landing runway just remember that it may be visible on base leg at night but it will not guarantee safe obstacle clearance until you are within the final approach splay.

You should never commence descent on base at night until you are 100% sure of safe obstacle clearance. Below the MDA obstacle clearance is your own responsibility

[Gary Lager]

Agreed Centauras - I also omitted such considerations from my post.

Last time I did one for real was about 2 1/2 years ago (LGKR). Definitely not a place to leave the MDA if not visual with the terrain between base and finals.

[Ibanez]

Centaurus - You have a very valid point..... Thank you.

[Sebastian Maguire]

Thank you everyone. Thats just what I needed and I think is pretty much identical to what the Ryanair captain talked about. Using the stopwatch, smooth and exact decent rates and adjusting for wind all sound like very interesting stuff to practice here on the sim.
I was wondering if there will be a day when all this can be done in VNAV only. I know the current Boeing VNAV function is overloaded with so many variables but it would be great just to hand fly the lateral part of the approach to your choosing and let a VNAV type function control decent to plant you right on the numbers.
Is the "vertical heading" function on the bus good for circle to lands and is the the reason type-certification for the bus to land at london city been granted because it can punch in a vertical angle on the MCPU.
Lastly, is the only way for me to fly decents in "degrees" on the NG's by use of v/s or manual whilst glancing at the FMC?

Sorry for so many questions.

[Ibanez]

You can fly "descends in degrees" using the Flight Path Vector on the attitude indicator (FPV on your EFIS control panel). It gives you your flight path angle relative to the horizon line. For a 3° glide slope, put the top of the "birdie" on the horizon line. Some prefer not to use it, some do.

[Gary Lager]

Didn't know the 'bus (Which one?) could land at LCY.

Any aircraft shold be able to cope with non-standard glideslope angles, though performance (speed control on a steep GS/landing roll/GA performance) would probably have more to do with it than the ins and outs of the autoflight system.

I may be wrong though.

[Sebastian Maguire]

Once time is up, request landing flap, match the speed, set RWY heading and use V/S to start a 300fpm descend, complete landing checklist.

Ibanez,

Just out of interest, can you use the v/s on the 737NG without setting the Alt on MCP to "0" or landing altitude. My PMDG sim doesn't allow me to bust the missed approach altitude set on the MCP by using the vertical speed wheel to below the alt set.
Also a question on the Altitude display of the MCP. Why is it that an exact altitude can not be entered (or is this my sim again) on the MCP. Why am I constrained to 100ft increments in this instance and yet not when using the FMC and VNAV.

Thanks

Sebastian