Limits on DME Arc
 

What are the lateral limits for a DME arc approach? I thought it was plus or minus one mile but cannot find it documented.

Those are the limits we're told we can work to for the initial IR so guess that this would hold true an a day to day basis - i stand to be corrected however !:)

Where I am, I think it is +/- 2NM, unles otherwise stated on the approach plate. ie some airports require you to be no more than +1NM due to conflicting airspace.

On a large aircraft such as an MD-11 when flying a DME arc, is there any provision for the autoflight to maintain this DME arc or is the DME arc flown entirely by hand? I would imagine it'd be hard for the autoflight to do this.

I believe the answer lies in ICAO DOC 8168 PANS-OPS. From memory it is +/- 2.5 NM, but there was something about diminishing obstacle clearance the further you are from the arc.

+/- 2 NM is the answer.

In the Shakey Isles, NZ AIP ENR 1.5-28 tells us that we have 1000ft clearance from terrain or obstacles out to +/- 2.5 DME from the arc.

(edited for spelling)

Captain Smiley
 

DAL 2728 the Auto Pilot can fly fly it coupled to the FMS if it is in the dat base.
Airbond where did you get the + / - 2 limit from?

The primary obstacle clerance area is 2.5NM either side of track - minimum obstacle clearance is 300m/1000ft. The secondary areas are 2.5NM either side of the rpimary areas - MOC is 300m/1000ft at the inner edge reducing to zero at the outer edge.

If you are clever enough, and don't mind a bit of button pushing, a DME arc can be constructed with most models of older FMS's/GPS's, that are not in the data base, then use 'area nav' coupled to the autopilot, for quite accurate arc navigation..

And, yes, +/- 2nm is my understanding for the accuracy required, unless stated otherwise by OPS SPECS or the relevant civil aviation authority concerned.

+ 2nm in Oz, except where otherwise noted. The only place I'm aware of that varies this is NW to NE of YPPH where the Pearce RAAF base airspace causes the arcing limit to be +1nm.

DAL2728 As Smiley says, if it's in the Nav DB then arcing works well, if it's not, then its a series of straight lines, or modulating bank to waffle from one side of the arc to t'other and back again. :\

Yes, I believe that Oz uses +/- 2 NM for pilot tolerance on the arc (unless stated otherwise on the chart). I've always wondered how they arrived at this figure because, when I crunched the numbers based on Pans Ops design criteria (many, many years ago now), I came up with +/- 1 NM. Hence, the pilot tolerance for DME arc in PNG is in the books as +/- 1 NM.

Interesting question. I have always worked to the 2.5nm quoted by Reynolds No1 as far as the question "Did he exceed the cleared area?" goes, but apply a "Pilot Performance Standard", which is arbitrary and based on what the average pilot can do on our (helo) type. That limit is 0.5nm, which was also the limit used on IRTs when I did them in the RAF. Absolutely no documentary backup for that one, so shoot at will...but it does improve the standards.

For all IR rating tests in OZ +/- 2nm is the limit.
And as far as I know its the same in Europe under the JAR's.

Under FAA TERPS manual a DME arc has a width that is the same as an airway (4nm either side of centerline). However while demonstrating proficiency at tracking an arc the exam tolerances are limited to +//1nm.

The TERPS limit is 1nm, PANSOPS 2nm.

Sounds authoritative, Dan, but can we have references? The original question said he couldn't find it documented. I've only succeeded in finding the reference to Primary and Secondary areas in PANSOPS, and that's 2.5nm.