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DME/VOR approach

Pro Member Captain
Kareem El-Sadi (crosscheck9) Captain

Can someone please explain the concept of a DME/VOR approach. I remember watching a video in the past, and the aircraft immediately turned and witihin seconds, it touched down. The cameraman said it was because the aircraft was configured for a DME/VOR approach. Thank you in advance.

Don Wood Guest

A simple VOR DME approach is nothing more than a regular VOR approach in which a DME fix is necessary along the final approach path to define when the pilot may begin a descent to a lower specified altitude.

A more complex VOR DME approach is one in which the DME must be used to fly an arc to arrive at a postion where the pilot can turn to his/her final approach course. This is often used in cases where there is high terrain that would interfere with a long final approach course. In that case, the published approach would call for approaching the airport from one side or the other, once reaching a measured distance from the DME, flying an arc toward the final approach path maintaining the stated distance from the DME, then turning onto the final approach path once you reach it. For an example, you can go to airnav.com and download the VOR/DME Rwy 34 approach at St. George, Utah (SGU).

In either case, in order to execute a VOR DME approach, the aircraft must be equipped with a DME and it must be used during the approach.

VOR DME arcs are among the most difficult skills a new IFR pilot must master and, unfortunately, there are not very many such approaches so it is hard to maintain that skill. This is one of the uses I have for FS9. When I maintain my competency at such manuevers in FS9, it makes it easier for me to maintain the same skill in the aircraft.

Pro Member Captain
Bindolaf Captain

The dreaded DME arc!

I have tried it (in FS, I'm not a real pilot) with only moderate success. A very nice one is the approach to LGIO, arc in the mountains to land in a valley of sorts. I've read a couple of tutorials, but if you want to give a couple of tips, Don, that would be great.

As for regular VOR/DME Don is - as always - right.

Pro Member First Officer
JTH First Officer

I (now) understand VOR, but what's DME?

Pro Member Captain
Kareem El-Sadi (crosscheck9) Captain

JTH wrote:

I (now) understand VOR, but what's DME?

DME is as it sounds; "Distance Measuring Equipment." It measures the aircrafts distance from a waypoint. Eg. your flying out bound of a VOR, and 55 miles out, you have to turn right heading 120. The only way you'd know your 55 miles out, is using the DME.

Pro Member Captain
jarred_01 Captain

DME also calculates the time that it will take you to travel to the waypoint, e.g. 45 minutes.

DME Wiki Page:

http://en.wikipedia.org/wiki/Distance_Measuring_Equipment

Don Wood Guest

Bindolaf - the only advice I can give you to perfect flying a DME arc is to practice, practice, practice. In theory, flying an arc is simple. You simply begin and maintain a very shallow turn that allows you to remain a constant distance from the DME. As I said in my previous post, to actually do that is extremely difficult and requires frequent practice to maintain proficiency.

Jarred-o1 - DME will only accurately measure speed and estimated time enroute if you are heading directly to or away from a DME. If you are flying at an angle to the DME, it will still show you a ground speed and ETA but it will not be accurate.

Crosscheck9 - DME does not actually measure distance from a waypoint. It measures distance from a DME radio transmitter. There are many other kinds of waypoints where DME is not available.

DME transmitters are co-located with some VORs. If a VOR has a DME, it is called either a VORTAC or a VOR/DME (they are different-the terms are not synonomous but both have DME capability). Check the legend portion of any sectional or WAC to see the various symbols used to represent these three types of VOR. There are also a few NDB's that have co-located DMEs.

Pro Member First Officer
JTH First Officer

Thanks for the explanations guys. I knew about that little screen that shows the distance to the VOR station and your ETA but I didn't know what it was called.

Also, thanks to Don Wood I now know that VORTAC is simply a VOR with DME (which from my experience almost all VORs have anyway). I had seen VORTAC written on a Virtual Airline sight but I didn't know what it meant.

Don Wood Guest

JTH: Actually, a VORTAC is more than just a VOR with a DME. The TAC part of VORTAC stands for Tactical Area Navigation or TACAN. A VORTAC transmits on both VHF and UHF - VHF for civil aviation and UHF for military aviation. The three types of VOR are:

VOR - VHF navigation
VOR/DME - VHF navigation with distance measuring
VORTAC - VHF and UHF navigation with distance measuring

There are also TACAN facilities not assoctiated with VORs but since these are for military use only, they are not a factor in this discussion.

I don't know whether most (50%+) VORs have DME or not but there are still quite a few VORs around the country that do not have DME.

Pro Member First Officer
JTH First Officer

Okay thanks 🙂

Guest

TACAN originated as a military aviation aid for bearing and distance fixing.
It is more accurate than a VOR/DME nd enabled air-air rendevouz for refuelling aircraft. Civil aircraft may not be capable of tuning into TACAN,
depending on the cxapability of the onboard receiver. Thanks.
V H KARMARKAR

Pro Member Chief Captain
Tailhook Chief Captain

Bindolaf wrote:

The dreaded DME arc!

I have tried it (in FS, I'm not a real pilot) with only moderate success. A very nice one is the approach to LGIO, arc in the mountains to land in a valley of sorts. I've read a couple of tutorials, but if you want to give a couple of tips, Don, that would be great.

As for regular VOR/DME Don is - as always - right.

I've actually just started a new topic here ➡ https://forum.flyawaysimulation.com/forum/topic/10098/flying-dme-arcs/

I want to make it clear that in no way do I wish to denigrate Don Wood's and other's contribution here ❗

- I do feel though that at times it can be beneficial to contemplate the same issue from different angles; even if it's only the different vocabulary another author/compiler of instructions uses.

I hope this makes sense 🍅 Surrender

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