BOAC:

I believe that's about TAS increasing with the elevation of the airport.

But, here are the three pages of FAA TERPs criteria for your assessment:

http://tinyurl.com/celrhbp

Thanks for the drop, but that doesn't really answer the question - and the 'airport elevation' does not change!

The only (drop) bit (Section 6 - 260 I cannot follow is
"and the evaluation of the final segment delivering the aircraft to the circling area. Also see Vol. 1, chapter 3, paragraph 3.2.1b." whatever that means - that is the only factor I can see that might produce different numbers - but does not at all other airports we know of.

Is there anyone around who produces charts who can have a crack at this puzzle?

BOAC:

A link to the entire order:

http://www.faa.gov/documentLibrary/m..._Chgs_1-25.pdf

terpster,

The FAA madness continues.... Change 26

perhaps someday, they will make the entire 8260 digital, not photocopied, so it can be searched....

OT... years ago, I saw a draft 8260.52A, that was supposed to align .52 with ICAO...have you seen that around somewhere and who might be working on it, if anyone??

FPOBN - I take it you have no explanation for the 3 different CMs?

BOAC,

It might have to do with

"5.4.4 OCA/H for visual manoeuvring (circling)
The OCA/H for visual manoeuvring (circling) shall provide the minimum obstacle clearance (MOC) over the highest obstacle in the visual manoeuvring (circling) area as specified in Table I-4-7-3 of Chapter 7. It shall also be:
a) above the lower limits (also specified in Table I-4-7-3); and
b) not less than the OCA/H calculated for the instrument approach procedure which leads to the circling manoeuvre. See Chapter 7, “ Visual manoeuvring (circling) area”."

With the different approaches they have different "OCA/H calculated for the instrument approach procedure which leads to the circling manoeuvre" because of the different splays due to the accuracy of each approach design final segments.

swh - we looked at that in post#15 for Monterey. I don't see the approach minima being the restriction on these approaches from post #47?

A nymphomaniac who is turned on by Oklahomans that post on Pprune, I'll bet.

GF

I know its a bit radical and out left field but hey why not just round up the highest to the next 100' i.e. 4800 and fly that? I am an old simple pilot and believe in the KISS principle …. Keep It Simple Stupid. You only have so many heartbeats don't use them up so fast.

Careful, OK - you'll get Slasher here PDQ with those sort of posts.....................:)

Back to the CTL - it is interesting that 2 of the 3 CMs breach EU-OPS minimum MDH for Cat C circling (600').

I think all we can assume is that someone might have been a bit too far into the Jack Daniels when the charts were drawn?

How will one distinguish the 'revised' (PANSOPS) CM from the 'old' (TERPS) CM on an FAA chart?

In flight you have to obey to the Captain

Harping back on this topic in the thread I would draw people's attention to the thread on the Bali B737 crash. It would seem the captain followed my earlier scenario of "keep going.......oops, wrong again."

What happened to F/O's having a self preservation button somewhere in the area of the TOGA button; or at least a loud voice?

One guess, dirigisme, French for "I have control"

GF

BOAC:

FAA uses TERPs and only TERPs.

I don't assume that so please don't speak on my behalf.

Different speeds as it always has been.

Pilots should be aware that there are significant differences in obstacle clearance criteria between procedures designed in accordance with ICAO PANS-OPS and US TERPS. This is especially true in respect of Circling Approaches where the assumed radius of turn and minimum obstacle clearance are markedly different

From May 2, 2013, the FAA started publishing new instrument approach plates that include an enlarged segment of airspace to protect aircraft during circling approaches. The new airspace also offers pilots additional obstacle clearance while considering their MSL altitude above the MDA, which affects true airspeed. The boundaries of protected airspace for circling approaches are defined by arcs drawn from the threshold of each runway at an airport. The larger the aircraft, the larger the arc. Previous versions of the FAA’s terminal instrument procedures (Terps) used a radius of 1.7 nm from the end of the runway for a Category C aircraft such as a Hawker 800. Under the new criteria that radius will increase by 65 percent, to 2.7 nm. Chart providers U.S. Terminal Procedures and Jeppesen both plan to use new chart symbology to identify the updated approaches. The government plates will show an inverse “C” in a black box in the approach minimums area of the plate, while Jeppesen will use a “C” inside a black diamond. Charts without the new designation will continue to be guided by the old, smaller-radii criteria.

Jepp Charts:
http://www.skybrary.aero/images/JepAC.jpg

edit: Govt Charts
http://www.nbaa.org/ops/airspace/iss...nima-chart.jpg

Circling Approach - difference between ICAO PANS-OPS and US TERPS

"The government plates will show an inverse “C” in a black box in the approach minimums area of the plate,". Thanks FPOBN

The TERPS/PANSOPS thing has been done to death here so many times it really does not need doing again! I was hoping our 'charters' here might be able to offer an explanation for the 3 different circling minima, but it appears they are flummoxed too.

Let's try a really simple question for someone:
Is it safe at Lewiston to fly the VOR 08 to circle at 4660' which is 120' lower than the safe circling from an LNAV approach to 08 and lower than the circle from the 26 approach - and why? I thought circling areas were fixed in geometry on airfield/runway characteristics so should not change, (barring approach minima issues, but here both less than 4660'). Presumably the circling area must change, but why?

The geometry is not fixed, it varies with altitude and aircraft CAT...

http://operationsbasednavigation.com....-17-08.51.jpg

CAT A and CAT B are close, so they can have one circling MDA, while CAT C is much larger, and CAT D even larger differences in radii....

edit:
Here is the proposed change to the charts on the CAT Radius.

http://operationsbasednavigation.com...8807195401.jpg


RNP charts dont have to deal with this! :E

- Lewiston - same airfield elevation, Cat C same Category??

I'll try it more simply - can circling area geometry vary for the same airport and same aircraft cat - and how?

EDIT: - why? Is circling abandoned with RNP charts?

EDIT 2: Shouldn't the Cat C and D be 3 and 4nm?

not airfield elevation...MDA of circling.

We are going around in circles here! :) Original question - how can you have 3 different CMs for the same airfield, same a/c Cat?

Q1- can circling area geometry vary for the same airport and same aircraft cat - and how?

a) I assume you take the obstacles within the altitude adjusted radius and add 300'?
b) If this pushes the CM into the next altitude band, you redo it at the new radius and iterate if required?

There we are - 1 CM surely?

Q2 - RNP/CTL?

Good comment, add it to living with the FAA....

RNP are coded procedures, there is no circling...you are on it or not.


I dont know why there are the differences at Lewiston, and I really dont want to get into laying out the circling diagram...but I will leave you with this figure 2 to ponder, consider the different variables, (and really be concerned about how many mistakes can be found on charts or in the navdatabase)

http://operationsbasednavigation.com....-17-11.47.jpg