VOR ranges - are they accurate in MSFS ?

[Paul K 1,332]

A few days ago I was flying the Just Flight Arrow from Aleppo to Baghdad, using only radio navaids and Little Nav Map. This leg of the flight was from the VOR at Deir Zor (DRZ) to the VOR at Baghdad (BGD), a distance of 236nm, on the 116 radial, and at a constant height of 5,500ft. Both VOR types are designated 'High' and both have a stated range of 130nm.

Therefore, I assumed that with the VOR ranges stated, there would be an overlap period in the middle of the flight where both VORs would be detected ( i.e. combined range of VORs = 260nm, while the leg distance was 236nm, and so giving an overlap in the middle of 24nm). However, the signal from DRZ behind me was still being detected at a range of 190nm, while the signal from BGD ahead wasn't detected until I was only 35nm from it.

In short, with stated ranges of 130nm, one VOR ( DRZ ) was still showing 190nm away, while the other, BGD, didn't show until I was only 35nm from it.

Can anyone explain this ? And while we're on the topic - NDB ranges seem to vary either side of their stated value too. But it's the VORs I'm mainly concerned about.

Quick Edit. Terrain height wasn't a factor, going by Little Nav Map's elevation profile. The only high ground during this leg of the flight was between me and DRZ (the longer ranged VOR). There was nothing ahead to obscure BGD.

Edited April 12, 2022 by Paul K

[RandallR 446]

One source I have (see below) shows range below 18,000 ft to be approx. 40 nm:

Type:    VOR
Frequency:    110.60
Usage:    Both High and Low Level
Radio Class:    Normal anticipated interference-free service:
below 18,000 feet: 40nm
18,000 feet to FL450 - 130nm
Above FL450 - 100nm
Latitude:    33° 15' 38.40" N ( 33.2607)
Longitude:    044° 14' 57.00" E ( 44.2492)
Elevation:    00113 ft.
Magnetic Variation:    E003380 0703
World Area Code:    427
Slaved/Assigned Variation:    E00300798
Associated airport:    ORBS

[Paul K 1,332]

I've read those figures too, in my search for an explanation. The reduction in range fits BGD in this instance, but doesn't account for the extension in range (almost a 50% increase) of DRZ. As we're not in the real world, it must be coded into MSFS - but I wonder what the parameters are. What decides the range variations ?

[177B 730]

5500' is too low.

All the Victor airways around this area are marked FL18 or higher.

Check your Jeppeson Chart, for minimum altitude between points on airways.

[Paul K 1,332]

12 minutes ago, 177B said:

5500' is too low.

All the Victor airways around this area are marked FL18 or higher.

Check your Jeppeson Chart, for minimum altitude between points on airways.

I'm flying in a light GA aircraft - Just Flight's Arrow III, as stated in the opening post.

[RandallR 446]

29 minutes ago, Paul K said:

What decides the range variations ?

Hard to say.  One possibility is the altitude of the transmitter.  BGD is supposed to be at 110 ft, while DRZ is listed as 700 ft.

[Paul K 1,332]

2 minutes ago, RandallR said:

Hard to say.  One possibility is the altitude of the transmitter.  BGD is supposed to be at 110 ft, while DRZ is listed as 700 ft.

I know what you mean, but I can't see that a height difference of approx 600 feet should be programmed to cause those discrepancies, without any terrain blocking either beacon and while I'm at a constant altitude. How has Asobo coded this, I wonder.. ?

[177B 730]

20 minutes ago, Paul K said:

I'm flying in a light GA aircraft - Just Flight's Arrow III, as stated in the opening post.

You could try climbing to 10,000' or a bit more. If you can stay VFR that is. I assume you are trying VFR. 

Reception is the same in GA aircraft as well.

I am not sure where MSFS is getting its data from but it is very common to have bad VOR range at lower altitudes even in real life.

My point is just that you can look at IFR charts to get an idea of actual range of VORs by checking min airway altitude in area you are flying. Use the Low Airway charts.

I have found in real life sometimes reception is bad depending on how dry or wet the ground and atmosphere is. I doubt MSFS takes this into account though.

[Beardyman 604]

Navigraph Navdata Center application does not provide update to nav stations?

[JRBarrett 3,070]

12 minutes ago, Beardyman said:

Navigraph Navdata Center application does not provide update to nav stations?

It definitely does, and the ranges of all VORs are set to their published r/w values.

[Biggles2010 343]

4 hours ago, Paul K said:

Can anyone explain this ? And while we're on the topic - NDB ranges seem to vary either side of their stated value too. But it's the VORs I'm mainly concerned about.

The different ranges you experienced appears to be down to the sim, but the  VOR ranges stated in navigation documents are the maximum range you should expect, providing you are at a sufficient altitude. The VOR signal is best regarded as a line of sight signal. although there are various factors which can affect this to some extent, creating a minimal ability to follow the curvature of the earth. This cannot be relied on and the theories of atmospheric signal distortion get quite complicated.

From a quick google search, the maximum line of sight range, with your aircraft at 5500 feet and a beacon at 700 feet would be 136 Km.or about 74 Nm.

Real life ranges vary considerably from beacon to beacon, so do not expect to always achieve even the max theoretical range.

[Mace 1,927]

1 hour ago, Paul K said:

I know what you mean, but I can't see that a height difference of approx 600 feet should be programmed to cause those discrepancies, without any terrain blocking either beacon and while I'm at a constant altitude. How has Asobo coded this, I wonder.. ?

As JRBarrett said they are set to their real-world ranges.

So...I'd surmise that the Baghdad VOR is a "low altitude VOR"  -- that is, I believe, a classification of VOR transmitter...whereas Deir  Zor is a high altitude VOR, and high alt VOR's have greater range.

I know Deir Zor is a high altitude VOR because I've used it many times in the past for jetliner flying while passing thru that region.  Whereas the Baghdad VOR -- no -- I haven't used it or do not recall using it.

BTW, that must have been an interesting flight, possibly seeing the Tigris / Euphrates and that whole nexus of desert and river.

[andyjohnston.net 617]

I asked a similar question not too long ago.  It used to be in previous versions, I could fly from my home at CYOW to KJFK using the respective VORs and there was plenty of overlap.  In MSFS the YOW VOR (freq 114.60) only seems to have a range of less than 30nm.

[Paul K 1,332]

1 hour ago, Mace said:

As JRBarrett said they are set to their real-world ranges.

So...I'd surmise that the Baghdad VOR is a "low altitude VOR"  -- that is, I believe, a classification of VOR transmitter...whereas Deir  Zor is a high altitude VOR, and high alt VOR's have greater range.

I know Deir Zor is a high altitude VOR because I've used it many times in the past for jetliner flying while passing thru that region.  Whereas the Baghdad VOR -- no -- I haven't used it or do not recall using it.

BTW, that must have been an interesting flight, possibly seeing the Tigris / Euphrates and that whole nexus of desert and river.

I'm going by the ranges given in Little Nav Map. Both VORs are classified as High, with the ranges for both stated as 130 nm. It must be LNM data that's wrong, and BGD is a Low VOR. I could understand it if the sim replicated reduced range when flying at lower altitudes, but that wouldn't explain why DRZ's range increased from 130 to 190 nautical miles!  I'll check it when I continue my flight.

Yes, it's certainly an interesting flight- I'm following the route taken by DH.88 Comet G-ACSR in the 1934 MacRobertson Trophy race, using VFR, VORs and NDBs only - no GPS allowed! I flew parallel with the Euphrates for a while on this leg. France, Italy and Greece were wonderful - loads to see in the world of MSFS. I love this sim, VOR peculiarities notwithstanding. 😉

 

[JRBarrett 3,070]

In LNM with Navigraph active, BGH shows as an H VOR. With Navigraph inactive, it shows as a T (terminal) VOR, which would have a very low range.