DME arc??

[air_cowboy]

hi all...
does ICAO specify config to fly a dme arc or maybe even speed??

looking forward to replys....

thanks...

[Semu]

No. Typically they are part of a procedure, and so would be subject to those limits. I suspect that for most of them you want to be going fairly slow, since many of the ones you are likely to actually fly seem to be inside the Andes.

[air_cowboy]

believe it to be flap 1 ..

[Capt Claret]

No mandate in Aus, though individual procedures may have a speed limit (eg 24DME arc, south of YBCS on Hendo STAR - 210kias to minimise chance of GPWS alert).

[Alteburger]

Have recently been looking into this myself and my interpretation is as follows - If the DME arc forms part of an initial approach procedure, PANS-OPS promulgates the acceptable speed range dependent on the category of aircraft that the procedure is designed for, or restricted to. (Cat C 160 to 240kts). While the procedure design does allow for winds aloft to affect the ground track, PANS-OPS also states that for this type of procedure, you only get the full 984ft (300m) of terrain clearance within 2.5nm of the DME arc centreline and so in some conditions, lower speeds may well be advised to remain within this area.

[411A]

For a quick approach, and with an OK from ATC...use 300 KIAS occasionally.
Works like a charm.

[pilotbear]

All opinions are valid, just adds to the discussion.

[Roger Greendeck]

Normal instrument approach speed limits (performance catagory specific) apply from the initial approach fix. If there is an arc before the IAF I am not aware of any limit on speed as long as you are within tracking tollerances.

[waren9]

What Alteburger said.

[air_cowboy]

Latest revelation... minimum clean speed

[mansah]

yes..just like what cowboy air said..minimum clean speed.. more time in hand for those tricky ones..:ok:

[Pilot Pete]

Read the question mansah;

does ICAO specify config to fly a dme arc or maybe even speed??


As pointed out by Alteburger, a speed range is specified under PANS-OPS, based on the category of aircraft if the arc is part of a procedure, from the Initial Approach Fix. A local AIP may stipulate a speed different to PANS-OPS (usually slower), as in the one quoted by Capt Claret. A procedure design expert would explain why, but I suspect it is because the specific range of speeds already mentioned would not allow clearance from terrain due to radius of arc.

Nowhere, does ICAO specify a config, because every aeroplane is different. By stipulating a speed (or speed range) they allow the operator to select an appropriate config to comply with the speed restriction(s).

So Air Cowboy, what is your reference for Latest revelation... minimum clean speed Perhaps a company restriction?

As an aside, the 160-240kts restiction for Category C aircraft (like the 737 and 757) is why the FMC descent speed defaults to 240kts below 10,000ft and not 250kts. You should hear some of the explainations I have heard for why it does that.............!

PP

[mustafagander]

PP, recall that the FMS will allow +/-10Kts.

BTW it's the same default speed on cat D a/c.

[Jimmy Do Little]

Here’s a rather simple way to look at it.

First, imagine that you are conducting a right hand visual approach to runway 36. Your track on the downwind leg would be 180(with speed and configuration appropriate) and the track on the base leg would be 270 (again, with speed and configuration appropriate). When the aircraft is about 45 degrees to the runway, you make the turn to base, etc, etc. Simple enough.

Now, you are flying the DME arc to this same airport. At some point during this ARC procedure, you will be “Downwind” (This point may be a lead radial / distance to the ARC). Then, at some point you will be on “Base” during the ARC procedure. Configure the aircraft appropriately and all works just fine.

The real issue is that of “Situational Awareness”. All too often people get caught up in the ARC itself and loose the basics of “Where are we” in relation to the bigger picture.

Keep in mind where you are, and the ARC becomes as simple as the visual approach referenced above.

[Pilot Pete]

BTW it's the same default speed on cat D a/c. Not so, certainly with our 767s, which default to 250kts, so your +/- 10kts theory does not apply there then.

PP

[Spunky Monkey]

Just a question n the minimum clean speed.
I agree that it makes more sense, however if the a/c is at min Clean speed and you bank hard to captue the inbound radial or the ILS then surely the margin above the stall is greatly reduced.
Would it therefore be better to fly Min Clean Speed +10kts or apply the first stage of flap before the final part of the arc.
Any guidance would be appreciated.

Some aircraft default to a lower speed due to the risk of birdstrike below FL100 or FL80. Could this be a reason?

[hoover1]

i think that the speed depends on how far out the arc is. if you have 20+ NM to go then why fly slow. In the 737 i usually fly it at 250 if there is greater than 10nm final. that way it is a steady 5 - 10 degree bank all the way around.

[Weapons_Hot]

Pilot Pete

A DME arc is designed for terrain clearance and traffic flow. Speed is generally irrelevant, unless there is a possibility of GPWS activation due to rate of closure to rising terrain beneath the arc.

Alteburger:

Winds aloft vs. ground track are irrelevant when flying a DME arc - the arc is to be flown within tolerances. Making allowances for wind to achieve this is part of pilot skills.

My $0.20 worth. :ok:

[smith]

Radius of a turn is totally dependant on speed. The greater the speed the larger the radius, therefore a DME arc must be limited by speed at some point.

[Spooky 2]

Okay I'll bite. I have chewing on this for a week or more now and for some reason it does not compute. The B777, be it a -200 or a -300 uses the 240 kts below 10,000 on the FMS as well. Both of these are class D aircraft... so how do you figure the defaults for these aircraft? Just trying to make some logic of your earlier statement.

[Callsign Kilo]

Flew into LFMN / NCE yesterday. Noted the 'Saleya' Circling procedure with prescribed tracks for 22L/R utilizes a 20 DME arc from the AZR VOR. It expects you to be at MAX 200KIAS and 4000' upon completion of the arc. This is around Min Clean on the 737-800.

Again another destination that I have been to recently (EGCN / DSA) utilizes a 12D arc to established onto the LOC for the ILS. No speed guidance issued on the plate. So practice standard speeds when applicable or permitted.

220KIAS at the IAF and 180KIAS on base. So I'm flying between these speeds. Always seems to work.

[fullyspooled]

I am not aware of any regulation that specifies speed limits for DME arc procedures as such, but clearly there may be restrictions in place for some specific approaches, and of course there is the 250 kt limit below FL100 for traffic not granted "high speed."

As much as I hate to do it, on this occassion I have to agree with 411A. If the arc is more than say 10 nm, and asuming high speed has been approved if below FL100, 300 kts does actually work like a charm. The bank angle is not as much as one might imaginge, but it is sufficient to assist adequate de-accelaration for config changes in the latter stages of an arc that intercepts the final approach course.

As an aside, although I agree with the genaral concept of SOP's, and the practice of flying "by numbers," I do sometimes wonder if the art of "airmanship" is being diluted as a result of them.

[Rick777]

I agree with Fullyspooled. While there isn't any rule about speed on all arcs there may very well be a speed limit on the place where you have to fly one or at least good airmanship may limit the speed you would want to fly.

[Spooky 2]

Most of the DME ARCS here in the US are within 10 miles of so of the FAF and the point where you would intercept the ARC at the IAF would dictate that you be down around flaps 5 in a B777, and somewhere roughly around 180Kts. If your going to be doing a VNAV approach with this ARC transition you need to get some flaps out for the "on approach logic" to kick in. I don't how anyone would do this approach maneuver clean, much less at 250kts?

[an3_bolt]

What Alteburger said. There are designed speed limits for the charted procedures if it complies with Pans Ops procedures.

Speed is specified in the Pan Ops criteria for the category of aircraft. Required max speeds are defined by the approach point ie initial approach etc.

There is a wealth of info on the jeppesen site regarding this stuff and more.
General Aviation IFR Chart Clinic - Jeppesen Supplies (http://www.jeppesen.com/personal-solutions/aviation/chart-clinic.jsp) and look under the chart clinic reprints.