Dme Arc Tolerance

[Sierra Charlie]

We have instrument rating tolerances published for ILS, VOR, NDB tracking etc but I cannot find any reference to the allowable tolerance when flying a DME ARC approach.
The A320/A330 FMGC does a pretty good job of flying these approaches but if it is not in the data base then what is the tolerance allowed either side of the ARC, +/- 1 nm, 2nm?

[OzExpat]

This probably depends on whether the arc is designed using TERPS or Pans Ops criteria. It might then depend on how the particular State's regulator has interpreted that criteria. The way it is in my dark corner of the world, the "flight technical tolerance" (i.e. the value you're seeking) is + or - 1 NM.

[mustafagander]

In Oz, DME arc tracking tolerance is +/- 2 NM. See AIP ENR 1.1 para 17.4.7 (c).

I would imagine that Oz uses ICAO tolerances, but I do not know for sure.

[Sierra Charlie]

OZ

thanks for your reply, interesting to hear from someone with your qualifiacations. I am working out of Hong Kong and am interested in the tolerances that would apply in this region. Out of interest is PNG based on TERPS mor PANSOPS?

[OzExpat]

It's Pans Ops in PNG. I read the same book as they do in Oz and I've disagreed with them over the interpretation of the derivation of the tracking tolerance. The way they read the book, they came up with + or - 2 NM but I came up with 1 NM. We agreed to differ...

[Pub User]

In the UK, the CAA guidance document for candidates for the initial instrument rating test states +- 1nm for DME arcs.

[OzExpat]

On my goodness... I actually agree with the UK CAA on something? :eek: Quick... somebody give me a valium! :D

[safetypee]

I refer to a very useful pilots’ guide on instrument flight procedures – “From Take Off to Landing”. This booklet was written by Olle Akerlind of SAS and published some time ago. A revised edition was published last year, sponsored by Honeywell Safety Systems (EGPWS) as a contribution to CFIT and ALAR. I regret that I cannot identify an easily accessible source for additional copies, but I recommend that you beg, borrow, or steal one that you may see.
The revised book refers to PANS-OPS and TERPS, but heed the usual warnings on master document revision status.

For PANS-OPS the primary area for obstacle clearance (984ft/300m), is 2.5 nm either side of the required track. There is a secondary area of a further 2.5 nm where the obstacle clearance reduces linearly from 984ft/300m to zero. Thus there is up to a 5nm wide corridor for a DME arc procedure.

For TERPS the primary area is 4 nm either side of the required track for an obstacle clearance of 1000ft. The secondary area is a further 2nm where the clearance starts at 500ft and reduces to zero. The minimum DME arc radius is 7nm (15nm for high level procedures).

I cannot find any reference for the required accuracy of flight (normally a value for flight technical error), but as with any flight procedure we should always aim for the highest accuracy.

[OzExpat]

safetypee...

The 2.5 NM primary area, under Pans Ops criteria, to which you refer is based on the route-sum-square value of several parameters. One of those parameters is "flight technical tolerance", which is allowance for the pilot's ability to maintain the required track.

Other considerations are applied, however, so it isn't a simple matter of saying that DME arc tracking tolerance is 2.5 NM.

[manuel ortiz]

Hello ,

Could anyone point out a source to obtain " From Take Off to Landing "

TKS

[zimi]

I refer to a very useful pilots’ guide on instrument flight procedures – “From Take Off to Landing”. This booklet was written by Olle Akerlind of SAS and published some time ago. A revised edition was published last year, sponsored by Honeywell Safety Systems (EGPWS) as a contribution to CFIT and ALAR. I regret that I cannot identify an easily accessible source for additional copies, but I recommend that you beg, borrow, or steal one that you may see.
The revised book refers to PANS-OPS and TERPS, but heed the usual warnings on master document revision status.
For PANS-OPS the primary area for obstacle clearance (984ft/300m), is 2.5 nm either side of the required track. There is a secondary area of a further 2.5 nm where the obstacle clearance reduces linearly from 984ft/300m to zero. Thus there is up to a 5nm wide corridor for a DME arc procedure.
For TERPS the primary area is 4 nm either side of the required track for an obstacle clearance of 1000ft. The secondary area is a further 2nm where the clearance starts at 500ft and reduces to zero. The minimum DME arc radius is 7nm (15nm for high level procedures).
I cannot find any reference for the required accuracy of flight (normally a value for flight technical error), but as with any flight procedure we should always aim for the highest accuracy.

The actual signal tolerance of the arc as PANS-OPS applies is ±0.25 NM + 1.25 of the distance from the DME antenna. The 2.5NMprimary/2.5NM secondary semi width is a) only for obstacle assessment (95%/99.7% containment areas) and b) only valid if the arc is on initial approach.

[Founder]

In sweden we fly at +- 0,5 Nm... I belive that it's the standard in Europe as well except for the UK where they do everything in their own way... =)

[757manipulator]

In sweden we fly at +- 0,5 Nm... I belive that it's the standard in Europe as well except for the UK where they do everything in their own way... =)

It mayby the standard in sweden...it certainly isnt in Germany or Spain, France, or come to think of it Italy either:ok:

Perhaps you are talking about the tolerances that you were trained too that were considered acceptable, many moons ago in a galaxy far far away 1/2 a mile each side of the arc sounds familiar:)

[flyboyike]

+/- 1nm in the US.

[Founder]

It mayby the standard in sweden...it certainly isnt in Germany or Spain, France, or come to think of it Italy either:ok:
Perhaps you are talking about the tolerances that you were trained too that were considered acceptable, many moons ago in a galaxy far far away 1/2 a mile each side of the arc sounds familiar:)

that's true =)

in my company we fly at +- 0,5 nm and that's also the margin that we've used in training... =)

[FlapsOne]

I've been through all of PANS Ops and I can find no reference to DME arc tolerances.

If anyone has found it please post a reference.

[keithl]

We train and test to +/- 0.5nm. We call it a "Pilot Performance standard", though, just to make it clear that its different from the PANSOPS tolerance. It is a standard which the average pilot can achieve, so that's what we aim at.

"SC" has asked a good question and I, too, would like to see something official on the subject.

[OzExpat]

G'day keithl mate!

Why did I know, waaay back in 2003, that this topic would come back to haunt me? And, given that I was aware of it, why didn't I resurrect all the work I did on it, many MANY years ago, to come up with a pilot tolerance of 1 NM? I guess the answer is that I put it all on a file, allllllll those years ago!:uhoh:

I'll try to find time to recreate the calculations that I used. However, in the meantime, I would just say that people should not automatically assume that Pans Ops is a "standard". It is not. It is a document, not an Annex, so there is no requirement for States to blindly follow it, for the simple reason that it provides guidance for procedure design, not how to fly the resultant procedures.

Sure, it provides information on the assumptions that are used to develop the design criteria for each type of approach. But the fact is that everything in it is the result of an RSS (route-sum-square) of the "assumed" values. It is not possible to specifically identify the contribution of each assumed value in such an equation. This is why there is such wide variation in the interpretation of the pilot tracking tolerance between States.

All we, as designers, can do is to take the basic data and interpret it in a way that works in our own environment. I agree that pilots should be able to fly an arc within + or - 1/2 NM of the nominal distance and, indeed, I've never had any problems with that. As others on this site can undoubtedly attest, I'm not the swishest IFR pilot around so, if I can fly within 1/2 NM on an arc, then everyone else should be able to achieve far better results!:}

It might take a while to reconstruct my calculations, so don't hold your breath waiting for it!;) Even then, it won't be authoritative across the world - just the way that resulted in the value that is used here.