Circling Minima
 

I'm sure there's a very simple explanation for this but I can't immediately think what it might be!

I've noticed that at a few airfields, circling minima for the same runway seems to vary depending on the instrument procedure you circle off.

Here's an example: at GCTS RW08, a CAT C aircraft can circle off an ILS/DME approach down to 1350ft, but off a VOR/DME approach the minima increases to 1720ft.

Most other airfields seem to have the same minima for circling regardless of the instrument procedure you fly. Is this specific to GCTS or is it something to do with the way the minima are constructed?

It has to do with very complex terrain and obstacle clearance criteria. If an approached is missed from a particular place, more obstacles and/or different terrain may come into play.

Okay, I'm going to go out on a limb and say you cannot transition from an ILS to a circling approach here in the US.:= That is unless you are using minima of 1000/3 or better for the circle. Go ahead I'm taking cover as I write this.

Sounds like a load of bollocks! :) If you're visually circling in the circling area, it doesn't matter how you got there or from what angle. Obstacle clearance in it is obstacle clearance. As for missed approaches, you'd always be doing those off the end of a straight segment, not operating inside the circling area, off the approach track, in IMC, surely? if you then do go IMC, well that's a different matter.

We use PANS OPS 4, and all our circling MDAs (and vis) are the same regardless of the approach used to get into the CA. Cat C: 4.2nm radius from the runway ends, 400ft above all obstacles anywhere in the CA.

Circling minima are not calculated with reference to a radio navigation aid - they are based on radii from landing thresholds. They can never be less than the straight-in minima for any approach.

It sounds as though the calculated circling minima at GCTS is 1350ft, but the VOR/DME straight-in minima is 1720ft - the circling minima must therefore be raised for that approach.

Spooky2

That might be correct on the 1000/3 for airlines, not so much for everyone else. Technically, an circling approach ends at the MDA, so one cannot use the ILS, but must circle from the LOC approach.

GF

GF,
What's your reference for this? Our country rules certainly have no such requirement, and practically, it doesn't make sense. Why does it matter how you get to the circling area (it may even be via a radar vector)? An ILS to a circle would be safer than a LLZ as you have vertical guidance down to the MDA.

Actually, a circling approach starts at the MDA (or DA). You cannot circle in IMC. A "circling approach" is in reality a visual manoeuvre after you have completed the instrument approach.

Only some airlines.
We regularly circle with 600-2 (or charted minima, whichever is higher) with a heavy jet.

Cap Bloggs

Well, yes, I agree, the instrument portion of a circling approach ends at the MDA, then it is a visual maneuver. Well, I'll have to do some research, as it was an USAF technicality that was more pedantic than real. The AF Instrument Manual also stated the FAF for an ILS was GP intercept, not the charted FAF that was used for timing on the LOC.

Let me see what I can find

GF

Here's the quote from AF Manual 11-217 Instrument Flight Procedures, for what it is worth:

GF

reynoldsno1:

I thought the same thing, but the straight-in minima for the VOR/DME on 08 is 950ft (3.5% missed approach gradient) or 1060ft (2.5% missed approach gradient) :confused:

Absolutely not dear G.F. all you have to do is to insert MDA for circling. Once on the ILS the decision to commence circle to land will be take on the MDA for C. to L. procedure.
Eurotraveller, you'll do the same for any IAP. the very much valid MDA is the one for circling approach not for VOR, ILS etc.
Cheerio. :ok:

Take a look at this and I think it will answer most of our questions or at least mine. http://www.jeppesen.com/download/aopa/jan00aopa.pdf

I quite familair with the airlines that use the 1000/3 restriction in their ops. Saves training time and eliminates the circle from their ops, thus eliminating just one more hazard from the daily scheme of things. Not a big deal to have the restriction removed from your certificate and some airlines that use expats want to see that removed prior to getting hired.

Slightly off topic but it is interesting to note the stark contrast between PANS OPS circling areas and TERPS. For cat C, they are 4.2nm and 1.7nm (from that article) respectively.

Trying to remain within 1.7nm of a runway threshold in a medium jet and do a stabilised approach from 4-500ft AGL would be very difficult with 30° AOB or less. No wonder Americans don't like doing circling approaches.:ouch:

GF
This doesn't really ring true to me. If you've not acquired suitable visual reference to continue the approach upon reaching circling minima then you go around no? Given a LPC (civvy I know but I can't think it'd be wildly different in the mil) expects the handling pilot to be able to maintain profile to not more than half scale deflection on the glide slope, and make account for a hotter than ISA day, then that pretty much defines the farthest out from the runway you could be upon reaching circling MDA. It's reasonably likely this will leave you more certain of position that any NPA, or am I missing something?

One more factor to consider on the B777 is that once below 1500' and coupled to the ILS you need to disconnect the AP to break off or deselect the approach. Someone mentioned that the cirlce is a visual maneuver and I agree but in the case of getting down to circling mins via the ILS, you want to be sure that the missed approach for the ILS runway is compatable with the missed approach for your circle runway.

While I presented what about 10,000 current and unknown, to me, USAF pilots have been taught for, at least, the last 40 years, I do not have the technical understanding of the guidance. BUT, let me ask this: At point on the approach will the MA be started, assuming one never broke cloud? Upon reaching the MDA, perhaps?

GF

galaxy flyer, one would discontinue the IAP at the minimum for circle to land (MDA) in case the visual cues aren't acquired as much as circle to land will be discontinued and MA for the IAP in use executed should the visual reference become insufficient. To picture it, let's say ILS 27 is IAP and the conditions aren't suitable to land on 27 but for 09. 09 doesn't have a IAP thus you will fly ILS 27 to circling minima MDA and circle to land on the 09. In case you decided to discontinue the circle to land you'll have to fly MA for the ILS 27.
Cheers.:ok:

I will quote from the B777 FCTM and I think it will answer your question at the same time.

"If a missed approach is required at any time while circling, make a climbing turn in the shortest distance toward the landing runway. This may result in a turn greater than 180 degrees to intercept the missed approach course. Continue the turn until established on a intercept heading to the missed approach course corressponding to the instrument approach that was just flown. Maintain the missed approach flap setting until close in maneuvering speed is completed".

So I believe the answer is that you would do the MAP procedure for the approach that took you to the MDA in the first place unless instructed otherwise by ATC.:ok:

Speak for yourself, Bub...:rolleyes:
On my heavy jet (category D...I don't fly medium jets, and have no desire to do so, either) we regularly circle at 600/2, without any difficulties.
IF you simply cannot do so in a category C jet...you don't belong at the pointy end.
IE: leave the flying to those that know how...even my 2000 hour First Officer can do this circling maneuver, with good results, every time.
Howsomever...IF you have a 200 hour wonder in the RHS, the Commander is supposed to know how to do these circling approaches...yes, even using TERPS.

Anyone else...baloney.
Harry Truman said it best...
'Can't stand the heat, stay out of the kitchen'.

NB.
Circling with a heavy jet during a type rating with the FAA, requires the maneuver to be completed under TERPS (read, FAA) to 600/2.
Can't do so...a pink slip is issued, forthwith...unless, your airline requires 1000/3, in which case, a circling limitation is placed on the license...VFR only.

We don't hire the latter types...and will not do so in the future.
Ever.

NB2.
We don't hire 'FMS operators/button pushers', without basic flying abilities, to do so would absolutely affect the bottom line...negatively.
And yes, we have an FMS (dual installation) the first on a wide body jet to incorporate complete LNAV/VNAV/engine thrust management, in one neat package.
It is called...a Lockheed L1011.
Thank you.