what is the accuracy reqd in DME arc

[stubby1]

hi friends,

while doing a, say, 12DME arc approach, what are the range of DMEs authorized? and where is it mentioned ?

thanks:ugh:

[PT6A]

When I did my training I had to do it within .5nm I think the IR pass/fail is 1nm.

[Checkboard]

Instrument approach tolerances are recommended in ICAO PANS-OPS, and are specified for each country in their respective AIP.

http://www.pprune.org/tech-log/76882-dme-arc-tolerance.html
http://www.pprune.org/tech-log/224286-limits-dme-arc.html

The UK-AIP is silent on the matter of DME arcs, and only specifies tolerances for ILS, VOR and NDB tracking:

UK AIP ENR 1.5 — HOLDING, APPROACH AND DEPARTURE PROCEDURES
3.15 Established

3.15.1 Aircraft are considered to be 'established' when they are within half full scale deflection for the ILS and VOR, or within ± 5°
of the required bearing for NDB(L).

... compared to the Australian AIP ENR, which states:
1.20.2 ... "Established" means being within half full scale deflection for the ILS, VOR and GPS, within ±5º of the required bearing for the NDB, or within ±2NM of the DME arc.

[aterpster]

The general testing standard is +/- 0.5 (one-half) nautical mile. +/- 2.0 miles is unsatisfactory in my view. The PANS-OPS arc primary containment area is +/- 3 miles and the DME can have a total error of 0.25 n.m.

[Checkboard]

I don't think the Australian standard is about maintaining the arc - that's pretty easy, I think it's about "As I am approaching the arc, when can I call my self "established" and thus descend in accordance with the procedure?"

So, with a 90º intercept onto the arc, you would start the turn at 220 odd knots at about 1.3 miles or so - and may commence descent (as you are within 2 miles).

[aterpster]

Checkboard:

So, with a 90º intercept onto the arc, you would start the turn at 220 odd knots at about 1.3 miles or so - and may commence descent (as you are within 2 miles).

Given that is the case, it is nonetheless poorly thought out and poorly worded. It should state "...within 2 miles of the arc..." not "+/- 2 miles."

And, two miles from the arc centerline is too far out to begin descent in any case. Descent should commence at the bisector of the turn onto the arc, just as in RNAV.

[capt. solipsist]

And remember the lead distance to turn into the arc at RATE 1: 10% of IAS

[Slasher]

Lead dist = 1% GS. So 200kt = 2nm. Works too.

I've always flown a DME yark within +/- 0.5nm, at which
point to adjust the heading towards the station.

[Checkboard]

Actually,

The Radius of Turn = Vsquared / [g.tanθ]

Where θ is the angle of bank, and V the TAS, you would then need to take the time of the turn to account for the wind effect.

For a 30º AoB turn, this equates fairly accurately to:

Radius = [V/200]squared

Using the circular slide rule (which I carry in the aircraft):

---Radius-------GS
-----+-------------+----
-----GS-----------400

So, for;
100 knots, Radius = 0.25 nm
200 knots, radius = 1 nm
250 knots, radius = 1.6 nm


... which is why I would start my turn at 1.3 miles or so at 220 knots .. but that's just me ;)

[aterpster]

Where to start the turn onto the arc and where to start the descent are two different, but related, issues.

[theficklefinger]

Gee whiz, it's a good thing you guys don't teach this stuff..

It's 1 mile inside or outside of the arc..there is no speed requirement other then airspace rules...so if under 10k, then 250kts would apply.

ATP standards, or professional standards may apply that once established, pro level would be to hold inside of a half mile in or out of the arc or better, depends on who's holding your feet to the fire.

[aterpster]

theficklefinger:

It's 1 mile inside or outside of the arc..

Reference?

[172_driver]

FAA PTS says 1 nm wiggle room. I believe JAA ride was the same.

In my opinion 1 % of GS is too early, at my speeds around 140 kts. I start 1 nm from the arc, slightly adjust the turn rate slightly as appropriate.

[Alteburger]

Protected range is published in PANS-OPS. 2.5nm from DME ARC centreline gives full clearance (Primary Area). For the next 2.5nm, terrain clearance linearly tapers to zero (Secondary area).

Speed limits are subject to procedure limit speeds (or more stringent if published). Generally 240kts for initial approach and reducing for final approach. Limiting speeds for each flight phase are published in PANS-OPS.

[Checkboard]

It's 1 mile inside or outside of the arc..there is no speed requirement other then airspace rules...so if under 10k, then 250kts would apply.

DME Arc procedures are almost invariably part of an instrument approach, so ICAO instrument approach limits after the IAF (and in the UK, the UK AIP limit of 180 knots) apply.

Please tell me YOU don't teach "this stuff". :ugh:

[stubby1]

Hi
I am still not sure what are the allowed limits while executing a DME arc.
Particularly interested for india.
thanks in advance

[172_driver]

What limit are you asking for then?

FAA Practical Test Standards: +/- 1 nm
PANS-OPS protected area: +/- 2,5 nm

So if you drift 1,5 nm off the arc your flying may be sloppy, but you are still within the protected area for the procedure.

[Checkboard]

Particularly interested for india.

You can have a look at The AIP India (http://www.aai.aero/public_notices/AIP_INDIA_MAIN.jsp) - my own quick look couldn't find a reference. The next step would be to look at an Instrument Rating test form (an Indian one, obviously) which should specify the testing standard for the officer conducting the test.

[Matt101]

Originally Posted by Checkboard
The Radius of Turn = Vsquared / [g.tanθ]

I found 0.5% of GS +0.1 always worked in practical and gives answers very close to the above formula in most normal speeds. 220x 0.005 +0.1 = 1.2 and your answer was 1.3 I believe. Just for speed on the go. Most instructors taught it.

Our JAA test tolerance was 1 nm though even the worst of students never let it much outside of 0.2 on a light aircraft. DME arc in a c172 is a lovely lazy way onto the ILS I thought...

[parabellum]

Used to do these regularly at Pago Pago as part of a base check, 2nm seemed to do the trick in a B737-200 at around 170-180kts. (Gravel Protect system fitted to u/c with speed limitation).

[despegue]

Regarding the Speeds to fly on a DME-arc...

This depends on the class of aircraft.

First of all, the poster that claimed 180kts. is a max on a dme-arc is talking absolute rubbish. Don't follow his/hers advice unless this is explicitly mentioned on your plates. This will cause disruption to the flow and irritated colegues and controllers.

Doc 8168 "Aircraft Operations" by ICAO has a table which is quite clear...
For example: Class C aircraft: min. 160kts. max. 240kts during the Initial Approach , which includes most DME-arcs. By the way, max speed for visual maneuvering is 180kts.

[aterpster]

An FAA DME arc can competently be flown as high as 250 KIAS. But, as the arc nears the intermediate segment a speed reduction is prudent, but not essential if the intermediate segment is of sufficient length to decelerate within that segment. After all, speed reduction is what the intermediate segment is for.

Although there is no stated speed limit on this arc, some prudence may be in order:

http://i201.photobucket.com/albums/aa214/aterpster/MGGTILSDMEARCRwy01.jpg

[Checkboard]

First of all, the poster that claimed 180kts. is a max on a dme-arc is talking absolute rubbish.

location: in my seat.

I assume you haven't read the UK AIP GEN 1.7 then :rolleyes:
Procedure speed restrictions.
Unless otherwise stated, procedures are speed restricted to a maximum IAS of 185 kt.

[aterpster]

Checkboard:

"Unless otherwise stated, procedures are speed restricted to a maximum IAS of 185 kt."

The context appears to me to apply only to departure procedures.

[despegue]

The ICAO doc 8168 is my bible, If the Brits want to do it differently, that they mention it clearly on the plates. I do not have an AIP of every third world country... by the way, haven't seen many arcs in the UK
:rolleyes:
Also, doc 8168 has procedures described as procedural turns. These are outbound/inbound turns ( and racetrack procedures). Do not confuse both.

[reynoldsno1]

That's a real tight arc at Guatemala - 7NM is the PANS OPS minimum, I imagine it is the same for TERPS?

[aterpster]

reynoldsno1:

That's a real tight arc at Guatemala - 7NM is the PANS OPS minimum, I imagine it is the same for TERPS?

Yes, 7 miles is also the TERPS minimum. But, TERPS provides more lateral protected airspace than does PANS-OPS for an arc.

One major U.S. airline that goes to MGGT considers it a special quals airport. Further, the IAP I posted is the only authorized ILS 1 IAP (there are also base-legs to the ILS.)

This particular air carrier limits speed to a maximum of 170 KIAS upon leaving 10,000 when IMC is anticipated, and final approach airspeed prior to rolling out onto the localizer. Makes sense to me having flown the procedure in Garmin's "simulator."

[Checkboard]

If the Brits want to do it differently, that they mention it clearly on the plates. I do not have an AIP of every third world country...
Pilot's who fly internationally are required to follow the laws of each country in which they are flying (just as a car driver must drive on the left, or right hand side). It is thus incumbent on international pilots (and you may one day grow up to be one ;) ) to read the "ICAO differences" section for each country in which they operate ...

... at the very least, it may save you the embarrassment of posting absolute comments such as "the poster that claimed 180kts. is a max on a dme-arc is talking absolute rubbish." when you later admit you don't know what you are talking about.

[bookworm]

Pilot's who fly internationally are required to follow the laws of each country in which they are flying (just as a car driver must drive on the left, or right hand side). It is thus incumbent on international pilots (and you may one day grow up to be one ) to read the "ICAO differences" section for each country in which they operate ...

Sure enough, in GEN 1.7 (http://www.ead.eurocontrol.int/eadbasic/pamslight-1B4AD6F2870D20368322123ED8553459/7FE5QZZF3FXUS/EN/AIP/GEN/EG_GEN_1_7_en_2011-05-05.pdf), that's what it says. But wouldn't you expect such a limitation to be mentioned in ENR 1.5 — HOLDING, APPROACH AND DEPARTURE PROCEDURES (http://www.ead.eurocontrol.int/eadbasic/pamslight-1B4AD6F2870D20368322123ED8553459/7FE5QZZF3FXUS/EN/AIP/ENR/EG_ENR_1_5_en_2003-02-20.pdf)? I think GEN 1.7 is intended to be informational, not the primary source of procedural design limitations.

[aterpster]

bookworm:

Sure enough, in GEN 1.7 (http://www.ead.eurocontrol.int/eadbasic/pamslight-1B4AD6F2870D20368322123ED8553459/7FE5QZZF3FXUS/EN/AIP/GEN/EG_GEN_1_7_en_2011-05-05.pdf), that's what it says. But wouldn't you expect such a limitation to be mentioned in ENR 1.5 — HOLDING, APPROACH AND DEPARTURE PROCEDURES (http://www.ead.eurocontrol.int/eadbasic/pamslight-1B4AD6F2870D20368322123ED8553459/7FE5QZZF3FXUS/EN/AIP/ENR/EG_ENR_1_5_en_2003-02-20.pdf)? I think GEN 1.7 is intended to be informational, not the primary source of procedural design limitations.

The context is departure procedures.

[bookworm]

GEN 1.7 actually mentions the limit twice, once in the context of departure procedures, the other in the context of Missed Approach Segment. But the question stands. Would you not expect the limitations to be detailed in ENR 1.5?

[aterpster]

bookworm:

GEN 1.7 actually mentions the limit twice, once in the context of departure procedures, the other in the context of Missed Approach Segment. But the question stands. Would you not expect the limitations to be detailed in ENR 1.5?

Both departures and missed approaches are closely related procedures. I don't know anything about ENR 1.5.

[photofly]

The Radius of Turn = Vsquared / [g.tanθ]...If you stick to standard rate turns, you're not bothered about the angle of bank.

The radius turns out to be V(kts)/187, in nm - which is pretty close to 0.5% of your speed. Make appropriate adjustments for wind.

[bubbers44]

I loved the DME arc from the north into Kingston. In our dinasaur B727 we started our turn 2.5 early to join the 15 DME arc at 250 knots and used the simple 1% lead to join and stay easily within .3 miles of arc. A gentle bank made it like a U control model airplane flying the arc. I used the rmi to simulate the control lines. It was so easy but fun.

[aterpster]

We have some dandies in FAAdom. Helena has a fair amount of traffic and no ATC radar below en route altitudes:

http://i201.photobucket.com/albums/aa214/aterpster/HLNILS27Z.jpg

[aterpster]

Approach speed briefing text for EGGW:

http://i201.photobucket.com/albums/aa214/aterpster/SpeedsatEGGW.jpg

[Avenger]

Well. as we fly all DME Arc in LNAV I would expect to see the appropriate RNP for the phase of flight, normally 0.3 for approach. While raw data monitoring is normal, no one in their right mind flys a commercial jet on a DME arc in HDG SEL..why would you? As for speed, VNAV will give a sensible speed base on the next limiting waypoint, as one contributor observed you would normally not fly a long arc at 180kts, in reality we could be 50 DME from touchdown.

[bubbers44]

My trusty 727 did great arcs at 250 knots using heading select. I didn't know I just had to find the LNAV and VNAV buttons. Actually most of the time I rolled into about an 8 degree bank so the bank never changed.

[Checkboard]

If you stick to standard rate turns, you're not bothered about the angle of bank.

The radius turns out to be V(kts)/187, in nm - which is pretty close to 0.5% of your speed. Make appropriate adjustments for wind.

You can try sticking to standard rate turns at 250 knots. :ooh:

[aterpster]

Avenger:

Well. as we fly all DME Arc in LNAV I would expect to see the appropriate RNP for the phase of flight, normally 0.3 for approach. While raw data monitoring is normal, no one in their right mind flys a commercial jet on a DME arc in HDG SEL..why would you? As for speed, VNAV will give a sensible speed base on the next limiting waypoint, as one contributor observed you would normally not fly a long arc at 180kts, in reality we could be 50 DME from touchdown.

A DME arc is an initial approach segment, so I would expect to see "terminal" or RNP 1.0.

[aterpster]

bubbers44:

My trusty 727 did great arcs at 250 knots using heading select. I didn't know I just had to find the LNAV and VNAV buttons. Actually most of the time I rolled into about an 8 degree bank so the bank never changed.

You must have had a lot better autopilot than we had on our 727s. Heading select for us would command a 25 degree bank for any significant heading change.

Having said that anyone proficient in a 727 should be able to fly a DME arc with the autopilot and FD turned off.

[Checkboard]

Well. as we fly all DME Arc in LNAV I would expect to see the appropriate RNP for the phase of flight, normally 0.3 for approach. While raw data monitoring is normal, no one in their right mind flys a commercial jet on a DME arc in HDG SEL..why would you? As for speed, VNAV will give a sensible speed base on the next limiting waypoint,...

That's right. It should be against the law to fly with out triple IRS, FMC, LNAV & VNAV - anything else is just dangerous. :hmm:

Children of the magenta line. :rolleyes: