View Full Version : DME arc maximum speed?

19th Sep 2004, 13:54
Is there an ICAO published maximum speed to fly a DME arc beyond the IAF? Similarly does anyone know of arc maximum speeds in USA, Europe, UK?

Many thanks in advance.

19th Sep 2004, 15:08
A DME arc is, I think, a part of the arrival/approach procedure. New PANS Ops distinguishes between aircraft categories, but typically, a cat C aircraft (Vat 121-140kt) will have a speed range of 160/240t during initial approach. A cat D aircraft (Vat 141/165) has a speed range of 185/250kt.

19th Sep 2004, 17:05
A valid question....I guess, if you're taking an academic test.

But in the real world flying jets...

210IAS for inital approach manuevers clean,
180IAS (intermediate flap) for intercept and manuevers final approach outside marker,
160IAS approaching marker (gear down/another flap)
APP+10 1000ft agl Final flaps

Never lose sight of the big picture...If you practice the ignorant art of "measuring with a micrometer", I can assure you .....you will lose your flying skills, your confidence, and your air sense.

For you new pilots.....Make sure that you place a good deal of common sense between theory and practice.

19th Sep 2004, 18:33
flying-elvis: thanks for your input. However, I've been flying jets for many years and I had a reason for asking the question. Any other answers, including any references would be very much appreciated.

19th Sep 2004, 19:35
My apologies. I should've made my "micrometer" comments a separate thread on CRM. But I see to many fine piloting skills ruined by the politicis of company check airmen.

19th Sep 2004, 21:21
Shame on me for trying to hijack this tread, but just when is one established / within limits on a DME-arc ?

20th Sep 2004, 09:07
A DME arc can be used within an Arrival segment, or Initial Approach, or even Intermediate Approach. Pans Ops speeds are different for each performance category, of course, and might differ in each of these segments. I say "might differ" because, while the Intermediate segment has no specific speed limit, it is assumed that pilots will be slowing down from Initial approach speed to the Final approach speed in this segment.

In some countries, speed in any of these segments might be further restricted by local rules, or even modified by a restriction on the particular chart.

Rules relating to "being established" on the arc can differ from State to State, based on their own interpretation of the protection parameters in Pans Ops, or on other factors that might be unique to a particular State. Off hand, I think that Australia allows a pilot to be established when within 2NM of the nominal radius. Here in PNG, it's necessary to be within 1NM.

Hope this helps.

20th Sep 2004, 09:34
Sorry I can't give you an ICAO answer, but a practical one may help. I have flown arcs at 210 kts in small turboprops but the turn on to the Final Approach Track / Localiser really is a knife edge well over max AoB to make the turn in time, and is far too gung-ho.

The same arcs I have flown in jets and would never recommend flying clean at 210. Initial approach flap for yor type and a speed of no more than 180kts. 160kts I have seen published in the standard profiles for two of the types I've flown, both jets.

And yes, I go with a mile either side of the arc and a sensible heading for being "established".

As a previous poster said, you can fly this too much on definitive theory rather than natural experience based skill. I would say however, that you won't go wrong flying the profile printed in your ops manual.

20th Sep 2004, 10:16
As far as I am aware there is no maximum speed for flying a DME arc. Obviously the speed would depend on what you are flying and how close the arc is to the airport. If it leads straight into the IAF then fly the speed as you would do on any other intermediate approach. Adjusting the speed and configuration depending on the distance from the airport the IAF is.
Lead and lag and if you get confused aim at the IAF.:sad:

20th Sep 2004, 10:54
If you're flying in Europe - get a copy of New Pans OPS.
TERPS, if flying in the States.

As for "established", I'd say you're well within limits if inside +/- 2.5NM of the published arc. The primary obstacle clearance area includes a 2.5NM sector on either side of the arc, where the obstacle clearance is minimum 300m. From there on, the obstacle clearance decreases linearly to zero, when reaching 5nm either side of the arc. According to NPO.

20th Sep 2004, 12:42
Crossunder - what is this "New Pans Ops"? Has it been re-issued, or something? If it replaces my "Pans Ops", I need to know.

21st Sep 2004, 09:25

I have flown arcs at 210 kts in small turboprops but the turn on to the Final Approach Track / Localiser really is a knife edge well over max AoB to make the turn in time, and is far too gung-ho.

I don't know what the official publications say in your part of the world but, here, they say that the 2NM lead for the turn off the DME arc will only work if your radius of turn is 2NM. Thus, if your speed produces a greater radius of turn, you need to start the turn sooner, to account for the radius. Of course, if you're going like a bat out of hell at the time, your turn radius could be so large as to take your aircraft out of the protection area.

Here's some figures, using Pans Ops calculations, to give you an idea of how it works out :-

Associated conditions :
Altitude : 4000 FT
Temp : ISA +15
AoB : 25 degrees
Wind : Assumed zero.

At 160 KIAS (174 KTAS) = 0.95 NM (rounded adversely)
At 180 KIAS (196 KTAS) = 1.21 NM (rounded adversely)
At 200 KIAS (218 KTAS) = 1.49 NM (rounded adversely)
At 220 KIAS (240 KTAS) = 1.80 NM (rounded adversely)
At 240 KIAS (261 KTAS) = 2.14 NM (rounded adversely)

Obviously some additional allowance might be wise, if you expect a tailwind during the turn, but the above figures should give you an idea of the base amount by which you need to lead the turn. As a matter of interest, the speed that comes closest to a 2NM turn radius in the above conditions is 232 KIAS (253 KTAS).

Thus, in zero wind conditions, a speed of about 230 KIAS is about the most that you can use with a sustained 25 degree AoB.

I'm with you, keithl! If there's a "new" Pans Ops, then I haven't got it either! :eek:

21st Sep 2004, 12:31
Thanks, OzEx, that's a relief. I thought I was being left behind in one of the few areas where I can still keep up!

21st Sep 2004, 13:46
Is it me or the thread missing the part that says you should most importantly stay within the speed limits prescribed at the given stage of approach, lest you aim to loose much more than just the piloting skills? Mostly applicable at "B" limited approaches where modern turboprops could easily overshoot any arc by a great margin in initial stages.

Also funny are the visual maneuvering radii at Greece, surprisingly about half of what you'd expect (based on TERPS, are they not?)


21st Sep 2004, 22:00
There is a big leap in turn radii between Cat B and Cat C aircraft - some, like the Metro and B1900, seem to fall between two stools. PANS OPS is being amended to reflect that operators must specify under which approach category they want particular aircraft types to be flown, and stick with it.

PANS OPS was developed from TERPS. In the intervening years, the two sets of criteria remain similar, with three main exceptions:
a. the missed approach
b. just about anything involving a turn
c. circling areas

c. is probably the most contentious, and the one area where US procedure specialists would agree TERPS is drastically inadequate.
The radii are far too small, and were probably one of the causal factors of the crash at Inchon a few years ago

21st Sep 2004, 22:47
Ozexpat -

The arcs I used to fly had a specified VOR radial that one had to cross which signified when the turn on to Final Approach Track / Localiser could be initiated.

With this printed on the plate there was no (approved) opportunity to start the turn early or late at pilot's discretion, so one was at the mercy of whatever speed the arc and final approach turn was designed for (again not printed).

Does this differ from your experience?

22nd Sep 2004, 09:21
Well now I'll try a second time to post my reply. The first time I tried to reply, the system accused me of not being logged in - and, of course, I then couldn't get back to what I'd written! :mad: Wonder if a ModBod can find out what happened there?

keithl... always a pleasure to help a colleague! :ok:

reynoldsno1... I've heard a suggestion that the small circling radii were considered to be a contributory factor in that nasty prang in Colorado some years ago. The way I heard it, the FAA made some slight changes to enlarge circling areas, as a result of that finding and that at least some folks in the FAA think the circling radii need to be the same as Pans Ops. Time will tell though, I guess.

Ojuka... your right about it being unwise to commence the turn prior to the lead radial. Pans Ops requires us to provide a lead radial/bearing that equates to a 2 NM turn radius and there is no requirement to protect an earlier turn. It seems to me that your only option is to select a speed that will keep your turn radius within the 2 NM provided by the procedure.

In PNG, we don't have a problem with turn radius for this manoeuvre because we impose an overall speed limit of 170 knots on Cat A/B for Initial Approach and 200 knots for Cat C/D. This invariably means that, in zero wind, the turn radius of every aircraft is comfortably within the turn radius limits.

I would've thought that, in other parts of the world, there would be a duty of care to make some sort of regulatory comment about speed in that turn, if there's no speed limit on the chart or in the rules.

Personally, I make the turn at 170 knots in the B200 and this almost always results in a turn radius of 1.5 NM. I do some simple maths to derive a lead radial that equates to 1.5 NM, instead of the 2 NM and this almost always works out spot on.

This might not be totally suitable in your area of operations, if you regularly experience strong winds. We don't usually have a major problem with that and, even if we do, it's more likely to be a headwind than a tailwind, so it's not as critical to the turn. However, it should give you a basis for experimentation - in good wx of course! ;)

22nd Sep 2004, 10:29
Following all this with interest, and I'd just like to pick up Ojuka's point here.
With this printed on the plate there was no (approved) opportunity to start the turn early or late at pilot's discretion
Earlier than the L/R, I agree - you're outside the procedure. But later is surely OK? You used the phrase "could be initiated", and that's the way I teach it. Our helicopters are obviously on the slow side of Cat A (no Cat H in UK) and turning at the L/R would be too soon, so I describe it as marking the point where "you are free to turn a/r for the Final Approach Track".

Any of you experts disagree with that?

23rd Sep 2004, 08:48
keithl... It's certainly difficult to conceive of an Authority that would not permit a turn at some appropriate point after passing the published Lead Radial. From memory (coz it's been a while since I've needed to look at it), Pans Ops requires publication of the lead radial as a warning that the aircraft is within 2NM of the next required track. Thus, it's up to the pilot to decide whether or not that is an appropriate distance to commence the turn off the arc.

There is certainly very little actual scope to commence the turn prior to the L/R so a pilot must anticipate the need to slow the aircraft to a speed where it can make a 2NM radius turn. But I'd be horrified if the official publications that Ojuka is using do not allow slower aircraft to proceed beyond the L/R before starting the turn. It is certainly allowed here in PNG and, I'm pretty sure, also in Oz.

Top marks for picking up that point - dunno how I missed it when reading his (or her?) post.

23rd Sep 2004, 22:12
Keithl and Ozexpat -

My point on the restriction of the lead-in radial was meant to emphasise that it is TOO LATE for arcs flown at high speed; I didn't mean that the turn in couldn't be left until AFTER for slower aircraft.I appreciate this of course. My misprint.

The whole jist of my input was that anything over 180kts is uncomfortable in my experience and doesn't give much time for error correction. In a nutshell!

24th Sep 2004, 08:58
I see where you're coming from now Ojuka. I've never seen anything in Pans Ops that justifies the selection of a lead distance of 2 NM. Indeed, my examples on page 1 suggest that there should be some sort of statement about the speed because the optimum speed for the turn does not equate well with the range of speeds for Initial Approach, particularly for Cat C/D types.

And, of course, the speed situation is much worse if the altitude involved in the manoeuvre is above the 4,000 feet that I used in my examples.

It has to be said though, that the most common usage involves a transition between Initial and Final Approach. Thus, pilots really should anticipate the need to slow down, to be able meet the speed range for Final Approach by the time they pass the FAF. Following this logic, it is probably a bit unreasonable to try to execute the turn at speeds above about 180 knots, as you say.

We can probably design a turn that caters for a larger radius, but there'd have to put a note about it on the chart because it differs from Pans Ops criteria. If we do all that, how do we provide an opportunity for pilots to slow their aircraft down for final approach? The only way is to build extra track miles into the procedure somewhere - making it longer to fly, less convenient for ATC traffic flow and more costly for aircraft operators.

I guess that we can't please everyone.

24th Sep 2004, 16:14
Very intersting thread..ill be watching..
Flew to Tabba,Egypt last night..the approach coming from the North was a 10 dme arc leading to a FAF at 7.6 dme(VOR DME).
Per boeing training 3 NM prior to FAF you have gear down flaps 15 150kts,2 nm prior flaps 25 140 kts,1nm prior falps 30 vref plus additive.
Our sop state that 3nm at the latest gear must be selected and flaps 15///
Coming from a 10 dm arc..it sounds dodjy...
VNAV was giving a arc speed of 220 kts..(minimum altitude is 4000ft at 10 dme..INCREASING to 6000ft at 12 DME!)
Here comes the question...
7.6 plus 10.6....when to select gear down..in the turn ?I agree open minded is also a quality...:-)
Doesnt Boeing stipulates that a circling (DME arc included?) max speed is 180kts?



24th Sep 2004, 16:46
I found the following useful advice from the booklet “From Take Off to Landing”. This is an unofficial guide to PANS-OPS and TERPS, but highly rated and reliable.

PANS-OPS:- “Lead radial (shown on approach chart) provides at least 2 NM lead for turn onto intermediate approach track.”

TERPS:- “When angle of interception of the intermediate course > 90 deg, a lead radial provides at least 2 NM lead for turn onto the intermediate approach course.”

The above is based on limiting the speed to that required (mandated) when flying the initial approach segment of any procedure; aircraft category:-
A: 90 - 150 kt
B: 120 - 180 kt
C: 160 - 240 kt
D: 185 - 250 kt

The obstacle clearance and procedure flight path are compensated for wind and altitude effects:-
Statistical or omnidirectional wind; 47 kt + 2 kt per each thousand of procedure altitude.
Bank angle. The lesser of 3 deg/s turn rate or 25 deg (the latter applies for TAS > 170 kt)

25th Sep 2004, 08:46
M.85... sounds like someone in the company should've done some trigonometry for you, to support the SOP. In the case that you've mentioned, you're 10 NM from the VOR/DME and you need to find a point that is 3 NM prior to the required final approach radial.

Therefore, arctan(3/10) = 16.7 degrees. Call it 17 degrees. Thus, you'll be 3 NM from the final approach track with a radial set up that is 17 degrees prior to the final approach radial. Surely someone in the company could translate that to the required radial for this approach at Tabba?

Finding a distance of 2 NM is achieved the same way :-

arctan(2/10) = 11.3 degrees. Call it 12 degrees and your lead radial for that position is 12 degrees prior to the final approach radial.

The Pans Ops forumula results in slightly different numbers :-

3 NM = 17.2 degrees
2 NM = 11.5 degrees

But it's all close enough for practical purposes. Maybe you can convey this to the folks who write your SOPs? In any event, I'd have thought that the company would've done this for you anyway, so that you'd know whether the lead radial for the turn is at 2 NM or 3 NM, or some other distance - a case of every little bit of information being helpful.

alf5071h... Spot on, as always. That's a good summary of the design requirements. :ok:

Semaphore Sam
25th Sep 2004, 12:33
I've always used a lead point of 1% Groundspeed, for 90 degree turn...200 GS = 2 miles, 300 = 3 miles. On 15 DME arc (4 degrees per mile), at 200 GS use 8 degrees lead, at 300 GS use 12 degrees. On 12 DME arc, same formula yields 10 degrees for 200 GS, 15 degrees for 300 GS, interpolate for different speeds and arc DMEs.

25th Sep 2004, 15:11
Semaphore Sam, flying is meant to be simple. There are many good rules of thumb for cross checking safety, but they should not take precedence over the basic rules for safe flying. This means that you must have a good understanding of approach procedures and that they must followed as published. Your rule of thumb may be adequate for most procedures, but somewhere, someday, there will be an exception. If you do not turn at the stipulated position on the chart then you may not have the advertised obstacle clearance; then what rule of thumb do you have for that?

OzExpat, thanks for the comment, but the accolade for this work resides with Mr Olle Akerlind, a retired SAS ground school instructor who wrote “From Take Off to Landing”, and also to Honeywell Safety Systems who republished the document 3-4 years ago as a CFIT ALAR safety initiative.

Semaphore Sam
26th Sep 2004, 14:55
I never meant to imply one should ignore published procedures, only to give a simple way to judge proper lead-points for a 90 degree turn from arc to course/radial. If the published turn-point is based on 180 GS, and your actual GS is 300, at least you can anticipate an overshoot. Also, many procedures don't have published lead-points. It's just a simple tool.

26th Sep 2004, 15:39
Semaphore Sam, I understand your point, I did not mean to imply otherwise. However, sometime it is the simple rules that we have misconceived or are using inappropriately that lead us into trouble.

My earlier post indicates that a good procedure design will accommodate a range of ground speeds (wind and altitude effects), and provided the aircraft is flown within the range of the procedure speeds (IAS) there should not be any flythrough or severe undershoot. But note that there are still many poor procedures published, which although meet the design requirements (PANS-OPS, TERPS) they are complicated / difficult to fly or have pitfalls for the unwary. These should be identified before the charts are used, but we (the operating industry) rarely complain or seek changes for the seemingly inconsequential issues.

For those who require the challenge of an example, see the DME Arc procedure for Ajaccio Corsica; spot the potential for an error – it’s not at the turn it point.

The generic problem is that we (pilots) often make up our own rules of thumb to counter problems, which in reality do not exist. In creating short cuts, we open the possibility to other errors based on our assumptions. Thus, a little knowledge is a dangerous thing, but pilots rarely have all of the required knowledge for completely safe flight.

27th Sep 2004, 10:49
pitfalls for the unwary. These should be identified before the charts are used, but we (the operating industry) rarely complain or seek changes for the seemingly inconsequential issues.
Drifting slightly off-topic here, but I think the main discussion's run its course.
When, in the Sim, we come across pitfalls, anomalies and even errors in procedures, I consider it my job to complain and seek changes. I have always had an excellent response from the procedure designers at CAA. And from the publishers of Plates, if that's where the error lies. So I'm making two points:

1. Sim instructors are the perfect people to identify and follow up procedure problems. That's why I follow threads like this one.
2. Changes and corrections can be done quickly and easily with just a phone call - in UK at any rate.


27th Sep 2004, 12:58


27th Sep 2004, 13:42
'I have always had an excellent response from the procedure designers at CAA'

keithl - Would it be possible for you to post contact details for these guys as there are one or two questions I would dearly like to get an official answer on.

28th Sep 2004, 11:55
Ok, Blue,
I'll PM you shortly when I've looked up the details. I'm not sure about actually posting the details to the world without their OK.

29th Sep 2004, 13:43
Well thanks guys, you've just given me an idea that should've occurred to me ages ago. In this dark corner of the planet, we're still developing our website so I'm going to see how practical it'll be to have a page devoted to procedure design FAQ... so to speak! I think it might help to resolve a lot of the problems that have come up. :ok:

29th Sep 2004, 15:39
http://uk.geocities.com/[email protected]/alf5071h_files/image001.jpg

Pitfalls for the unwary – Ajaccio

The DME Arc procedure is at 11 nm from ‘AJO’, but at the point that you join the arc from approach or the holding pattern the aircraft is also at 11 nm from the ILS DME ‘AC’. Note the speed restriction for the procedure and the lead in radial. Thus, for those of you who like to pre-select the ILS and have dual DME displays be very careful as to which DME you use; if you inadvertently fly 11 DME from ‘AC’ you get very close to the hills as you fly through the ILS centreline.

You would not make that mistake? Someone already has; and, but for a GPWS warning and good crew reaction there would have been a fatal accident.

29th Sep 2004, 18:07
What a great approach to use for training! It's got so many traps & complex holds/final intercept/MAPt/missed app intercept. If I were teaching again I'd love to set this up on a sim for IR students. Even a PC would be good.