DME ARC Approach Tutorial

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Postby nzav8tor » Fri Apr 06, 2007 12:35 am

Must have to much time on my hands...

Well I thought it prudent to continue with our Beech 1900D flight from Wellington on the DULEX TWO departure to a destination not to far away to demonstrate enroute navigation and also a non-precision approach.

Nelson serves as a good aerodrome for this example.

Using the flightsim flightplanner, I planned the flight using the H267 airway which is a line between WN VOR and NS VOR. The track is 250, this means we are tracking intially on the 250 Radial FROM WN VOR and eventually tracking
TO the NS VOR on the 070 Radial.

The trip distance is around 72 Nautical Miles. To calculate the cruise altitude I use my short cruise rule, useful for trips of less than 200 Nm.
So add 5 onto 70 makes 130. So a good cruise level would be FL130.
Unfortunately this is the transition altitude and also our track is slightly south so to conform to cruise level rules we need to choose an even level (our track is south of 270-090.)
We can't use FL140 or 14000' as this is in the transition layer between 13000' and FL150 and it doesn't make sense to climb too high for this short trip so I will take 12000' as the cruise altitude.

Will afford nice views over the sounds too.

So check now that this altitude is above enroute minimum safe altitude. This is done by referring to the enroute nav chart. MSA is 7600' so we are well above.

Ok, we have just reached DULEX at 4000' and are instructed to turn right on track and climb 12000'.

So first things first, set heading 300 for intercept and preselect 12000 on the altitude select.
Now engage HDG and ALT on the autopilot. This autopilot is not realistic with the climb function but it does a nice job most of the time. Set the climb bug on the VSI to around 2000 fpm climbing.

Ok now change the HSI radial to 250 using the OBS knob. As we are currently on the 204 radial we have quite a lot of space to cover to get onto the 250 so I have choosen heading 300 to cut across quickly.
Normally we would use around a 30 degree cut but it is important to get established on the airway sooner rather than later.

I arm NAV mode on the autopilot and reduce the cut as we get closer to the 250 radial. This makes it easier for the

autopilot to capture the radial and prevents to much chasing of the needle during the intercept.
Use your RMI to see where the radial is in relation to the 250. The nose of the green needle is pointing to the VOR, the tail is pointing to the radial. To get onto the right radial when flying away from the VOR we need to 'drag' the tail of the needle toward our desired radial. So say the tail of the green needle on the RMI is pointing to 240 we need to fly at a greater heading than this, say 260 to make it move toward 250.
The NBD is almost co-located with the VOR so you can use this on the HSI for for the same purpose too.

In my flight we captured the 250 radial at 20 DME from WN VOR, this is acceptable considering the SID finished at 10 DME.
And with good performance from the Beech we are already at cruising altitude 12000'.

user posted image

Ok, the NAV mode should capture so align the heading bug with the aircraft heading, this is useful in case NAV mode fails and we revert to HDG hold or if you want to adjust the nav setup and manually switch back to HDG, the bug is aligned already. Its just good practice to get into.

We are in the cruise phase of the flight so adjust power accordingly and perform the checklist.
The next thing to think about is, when do we change over to NS VOR?
Well the AIP for Nelson has an interesting page called MRA.This stands for Minimum Reception Altitude and it is the altitude above sea level which we can expect a reliable signal from the Nelson NS VOR.
Handy huh?

user posted image

Unfortunatley flightsim doesn't model the real weakness of navaids with variable recpetion ranges that are caused by terrain, time of day, atmospheric conditions and so on but in keeping true to life we can look at this chart to get an idea about when we can expect to recive a reliable signal from the NS VOR.

The chart is centred on NS VOR with a bunch of segment fanning outwards in a seemingly random pattern.
It doesn't take to much explaining. On the left of the VOR is marked 10 15 20 25 30 40. This is DME distance from the VOR and these 'range rings' scribe a circumference right around the VOR.
The dark black lines frame areas between certain radials and DME distances from the VOR and the number inside in the MRA. Got it?

Our track is 070 (even though we are flying heading 250 non wind corrected, the NS VOR radial is 070.)
So we find the 070 radial on the chart, there isn't one but there is a 075 so thats pretty close.
Within 10 DME the MRA between R-075 and R-015 is 7000. Then from 10 DME to 15 around the 070 is 11000 and finally from 15 DME to 25 it is 14000'.
Further away than this we can't expect to recieve a reliable signal. So we are at 12000 which means we can't expect to recieve a reliable signal until we are within 15 DME of the VOR.
This is not to good as we want to fly a 15 DME Arc but the chart has doesn't acount for increasing reliability as we get closer, so while the 14000' is MRA greater than 15 DME, it may be closer to 11000 between 15 and 20 DME.
So I would change Nav 1 to NS around 40 DME WN (just over half way) and see if I a getting a signal. Keep WN on Nav 2 incase the NS signal is not to good. That way we still have a navaid to maintain the 250 track.

When changing Nav 1 from WN to NS make sure you first disengage NAV mode in the autopilot, if the signal is weak this may cause the autopilot to start rolling the aircraft left and right to try and capture the unsteady radial.
Use heading mode until signal reliablility is assured. (Generally within the MRA sector.)
Don't forget to Ident NS VOR to be sure it is the correct station.

In flightsim expect a good signal from NS well before the MRA chart suggests you should.
So, now tracking inbound NS keep 250 set on the HSI, no need to change it to 070, and re-engage NAV mode on the AP.

Now we dont have to much time left before descent and approach so we will make the approach briefing.

We will fly the Nelson VOR DME ALPHA approach.

user posted image

Read the approach plate in the same manner that we read the SID plate for Wellington.
At the top we have effective date and plate name, check and confirm.

Now we have the required frequencies, ATIS and Tower, the note says Tower controls the approach.
Below this is the NS VOR frequency 116.40. We already have it tuned and Idented.

Final approach course is 180 but this will come later.

Minimum altitude is 1500' at 6 DME.

Airport elev for pressurisation setting.

MSA diagram, very important. This is the minimum safe altitude to ensure terrain avoidance within a 25 DME radius of NS VOR. This is useful for our descent planning.

Next are missed approach instructions. Come back to them in a sec.
Altimetre info and tranisition info and some notes. Note 2 of particular interest.

For the approach itself.

The pictorial diagram is a nice one as it has some terrain relief depicted which is good for getting a mental picture of the 'lay of the land.'
You can see the runway and VOR located in the centre. The runway is orientated correctly 02/20 so this helps for building your picture too.

A semi circle is drawn around the VOR and it is labelled '15 DME Arc.'
This is what we will be flying to begin our approach.

In light grey there are a few radial points depicted intercepting the 15 DME Arc. Find the area where we are approaching from. There is a radial drawn at 070 which is perfect, makes life easy for us.
This shows that at 15 DME NS VOR, on the 070 radial (250 track) we can descend to 6500' when established on the arc.

This sounds a bit confusing but bare with me as we work through the procedure.

So we will turn RIGHT to join the arc and when passing the 035 radial we can continue descent to 4000.
Then after establishing inbound on the 180 radial we can descend according to the approach, so intially 2700' until passing 10 DME, then down to 1500' until 6 DME and then down to MDA - Minimum Descent Altitude until 1.5 DME.
This is the Missed Approach Point.

MDA is minimum descent altitude and is the lowest we can fly when in IMC.
Looking at the bottom of the chart there we can check what this is for us under Cat B, max airspeed for circling is

135 knots and MDA is 660' which is 643 above the ground. Minimum visibility is 2800 metres.
Because the inbound course is 180 and the runway is 02/20 this means we won't be lined up for a runway to land when we are at MDA. So therefore a pattern must be flown to line up on the runway and land.
This is called circling and there is an instruction we need to know. The bottom right diagram shows that circling is only allowed on the west of the runway extended centreline.

If we are not able to see the runway, runway lights are some other form of visual reference we must execute a missed approach.

In case of missed approach we now read from the top section, Climbing RIGHT turn to intercept NS R-315 outbound, turn RIGHT join 15 DME Arc and enter holding at TASMN at 4000.
The dotted line on the diagram shows this missed approach procedure.
In the top right is a box which shows the TASMN hold. It is an inbound course of 180 with RIGHT turns and we would make a parallel entry to establish.

Maybe I can explain holding procedures in another tutorial.

So briefing completed for now.

Back in the air we are getting pretty close to the NS 15 DME arc so we are thinking about our descent.
There is quite alot of arc to get around so we have plenty of time to descend from 12000' to 4000' when we are on the final segement before turning inbound so begin a descent to MSA taken from the plate when within 25 DME of NS.
This is 7600' in our sector. (I would make it 8000' to keep it as round numbers.)

Ok now for actually flying the procedure.

Check your groundspeed on the HSI. Use this as a rough estimate to when to begin the turn. In my example we are doing about 270 knots GS so that means I want to begin my RIGHT turn onto the arc at just under 18 DME.
(It will take 2.7 miles to turn through 90 degrees at 270 knots groundspeed - got it?)

Switch to heading mode. Change the OBS to course 240. The needle will deflect fully to the right.
Track the 070 radial using your RMI. When just inside 18 DME set the heading bug to 330.
The aircraft is now turing right to establish on the 15 DME arc.

user posted image

The DME will continue reducing until you are flying paralell to the station.
In a few seconds the needle will swing quite quickly across the HSI to become fully deflected to the left.
We have now crossed the 060 radial.
Using the chart we can see we can now descend to 6500' so set this on the altitude preselect.
You are established on the arc if you are +/- 1 DME from 15. So 14 - 16 DME is ok but try for 15 as close as you can.
The groundspeed will drop to zero as you are now flying parallel to the station. If it is increasing you are either

flying away or toward the station. Try and keep it at zero.

Set the HSI course to 230. Change heading bug to 320. Wait for the needle to pass through the centre again. Now set HSI course to 220. Turn left a further 10 degrees. Monitor the DME distance. If it is above 15 DME then turn left more to cut across the arc. If it is less than 15 DME turn right more to fly out on the arc.
Build the mental picture of where you are in relation to the 15 DME arc and the inbound course 180.

user posted image

When you have passed the 220 you can begin descent to 4000'. Select this on the altitude preselect.

When you reach course 190 aim to be decelerating and close to 4000'.
Begin a LEFT turn to 180 as soon as you cross the 190 radial, this is the turn to establish inbound.
Set HSI course to 180 and arm NAV mode again. This will be the approach itself.

user posted image

When the needle is within half deflection either side of the centre (180) you may begin descent to 2700'.
(This is +/- 5 degrees of the inbound course as the VOR needle moves in a 10 +/- degree sweep.)

Reduce speed to 200 knots and aim to be at 2700' before passing 10 DME.

user posted image

Then passing 10 DME select 1500' and continue descent.
Aim to be at 1500' at 7 DME.
Unlike a precision ILS approach, the altitude restrictions on a non precision approach are just minimums at a certain point. It is good practice to get down to the lowest altitude you are allowed to be at well before you cross the DME point.
You have more chance of getting visual and it is easier to configure the aircraft (flaps and gear) when you are not descending.

Aim to have approach flaps set before 6 DME and reduce speed to 150 KIAS.

user posted image

Passing 6 DME put the gear down and select 700' on the altitude preselect and down to this altitude by 3 DME. Then you have plenty of time to look out before you reach 1.5 DME where you must go around if you are not visual.

Make sure the heading bug is aligned with your heading a select HDG mode on the AP.

At the MAP you see that it is not a nice picture to land from here so turn right and climb to 1000' and join the downwind for runway 02.

user posted image

Passing abeam the threshold of runway 02 start timing for 1 minute.

user posted image

Reduce speed to 140 knots.

After 1 minute turn left to heading 020 and begin a gentle descent. When established on final 02 select full flap, perform final checklist and continue to land.

user posted image

Thats it, all done by the book.

Questions? Fire away...

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Postby Ian Warren » Fri Apr 06, 2007 12:46 am

Hi Dave , This effort ,the diagram and layout , superb , for the simmer and real pilot (simmer :) ) :thumbup: Thanx
There is never enough time , guessin a big thanx from a lot off newbies to yourself , and me . A great turtorial .

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Postby jastheace » Fri Apr 06, 2007 9:04 am

great, just got told off by the wife for printing it but hey, it is going to be a great help, thanks for the effort
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Postby ranm » Fri Apr 06, 2007 9:10 am

Dave, it's a beautiful thing ! :)

many many thanks - Ran.
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Postby towerguy » Fri Apr 06, 2007 9:16 am

this is excellent , thanks.

just a point of discussion - what are your opinions on the move internationally to make these approaches a 'constant rate of descent' approach? same for LLZ and LLZ/DME.? I am not sure myself which way to go as yet as there seem to be valid arguments on both sides, I'm just interested to hear a pilots perspective.

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Postby travnz » Fri Apr 06, 2007 3:59 pm

Ho much does it cost to have Jepview?
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Postby nzav8tor » Fri Apr 06, 2007 7:39 pm

Hi Craig,

Following your world tour posts, great fun, you should be writing a book and making some money - you obviously have the paitience and imagination for it!

From a pilots perspective a constant descent sounds like a nice concept, I am happy to not have to make step climbs and descents due ATC requirements.
It keeps the flight smoother for pax as there are no constant attitude and power changes and the VNAV path descent can do this nicely too in equipped aircraft.

It will certainly save some fuel for the heavies but its much of a muchness for smaller aircraft.

Certainly it won't be possible to make approaches like this everywhere as there is just to much traffic going in every direction but I'm sure we will see more refined STARS in the future which 'freeway' everyone onto the ILS.

In Vienna, Munich and other big airports there transitions to each runway which make a quite a long snake finishing just before the inital approach point or fix.
They have altitude constraints and if you can think ahead regarding traffic it is possible to guess what the controller is going to do with you, maybe shortcuts etc, and set a speed and descent rate to keep virtually constant till glideslope intercept.

I think I saw a post on these forums by someone recently who said they flew 747's, if he is out there, probably most qualified to respond...

As for jeppview, your gonna hate me for this.... I get it through work, remote access to every plate and enroute chart, IFR and VFR, constantly updated, worldwide coverage.... Hate to think what the company pays for that...

The coolest though is our brandnew jets have 'paperless' cockpits where we can bring up the plates on the MFD. The older captains cant get used to this and prefer the paper copy but I swear by it. You have a little stick to move around the plate and zoom in and out. Pretty neat.
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Postby towerguy » Tue Apr 10, 2007 7:42 am

thanks , it gives me some more to tink about. I may also hit you up for some info on systems at a later date if I may. I am slowly working on a Baron home cockpit system but may be looking towards doing a boeing at a later time (poss B747) and will need to know how systems move and feel as I can't get that type of info from photos. I did get some idea on my recent B747 simulator ride but I'm in my 40's now so the memory you now ... kinda fades ;)

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Postby ZK-TJL » Tue Apr 10, 2007 10:34 am

Super resource nzav8tor........Thanks heaps for putting this togeather!!!! It reads so well, very easy to follow and understand. Well done :thumbup: :clap:
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Postby gdavies » Mon Sep 10, 2007 8:30 pm

Great resource. notworthy.gif Are you able to recommend a book, web site or something that has more of this sort of stuff?

You talk about starting your turn to intersect the 15 DME arc at just under 18 DME, then explain the equation as "It will take 2.7 miles to turn through 90 degrees at 270 knots groundspeed - got it?". Sorry, but I don't get it. sad.gif I'm sure I've missed something there. Is there a rule of thumb you use? Or is my maths a bit wanting?

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Postby gdavies » Mon Sep 10, 2007 8:43 pm

Someone was asking about the cost for Jepview. The AIP NZ web site ( has a lot of this for free. Try the link called "Aerodrome Charts" and follow you nose ....
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Postby cowpatz » Wed Sep 12, 2007 12:06 am

The lead in is 10 % of your groundspeed so for a 180 kt G/S it would be 1.8 nm and 210 kt 2.1 etc.

The other factor to consider for your arc approach is the track miles around the arc. No point in descending too early and then having to waste fuel levelled out with power on. The way to do this is with the 1 in 60 rule. This rule essentially means that 1 degree over 60 units in length will be 1 unit wide. Therefore 1 degree over 60nm will be 1 nm. So what does this have to do with arcs?
Well most arcs are 10 nm in radius. 10 nm is equal to 1/6th of 60 therefore 1 degree will equal 1/6th nm around the arc. So 6 degrees of arc equals 1 nm. All you have to do is divide the number of degrees around the arc by 6 to get the distance to travel and you can use this when working out your descent distance.
For a 12 nm arc divide by 5 and a 15 nm arc by 4.

I am putting together a sort of guide on conducting Non precision approaches and it is in the Alpha stage at the moment (have a few screenies to add and to tidy up the text etc) but it covers FMC and non FMC non precision approaches and I use the NZNR 16 VOR/DME arc approach as a reference.

You could take a look at this website which has some useful information in it regarding IFR navigation for flight simmers.

Very much American but still has some useful sections in it.

Last edited by cowpatz on Wed Sep 12, 2007 12:12 am, edited 1 time in total.
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