It seems like LNM should be calculating the course in its flight plan table based on whichever VOR is called out in that table, per the snippet that I posted from the LNM manual above. I need to dig in a bit more there.
In the steam gauge C172, I’m actually even seeing slightly different behavior between the two different VOR gauges on the same aircraft, when set to the same radial. Super weird! (Edit: This may be an error unique to the Steam Gauge C172, other aircraft seem to be working OK per the updated post above)
I’m going to document this a bit better and then do a ZenDesk ticket. If it turns out to be avionics-specific I will raise it with the Working Title group.
I do not have access to Navigraph so I’m not sure how that could be impacting this.
On the topic of VOR CRSes in LittleNavMap - it looks like you have to include a waypoint inbetween the 2 VORs that compose an airway in LNM, then it will give you the correct CRS values based on the declination of the VORs.
With no waypoint, V430 between MOT and ISN shows up as 263 magnetic, not matching the IFR chart:
With a waypoint ERUVE added to the flight plan at the midpoint, it shows up as 258 M outbound from MOT (consistent with the IFR chart) and then 262 M inbound to ISN; 262 - 180 = 82 degrees radial inbound, which is within 1 degree of the chart. This seems to be accounting for the difference orientations of the MOT (13 degree east of true north) and ISN (7.9 degrees east of true north) VORs (perhaps with the small one degree error due to rounding in the math):
Interesting find! I tried to verify this with my EHK example. Unfortunately there are no named waypoints right on V235 nor on V293, so I added user waypoints about half distance right on the airway. It’s a mixed result - the first leg of V235 now shows 004 (closer to the 006 it should be), but the second leg still shows 000. Granted it’s not VOR to VOR but airport to VOR, so maybe that plays a role here. But for V293 which is VOR to VOR it still shows 083 / 084 (one degree difference in one leg compared to before), but it should be 88.
I’m testing more aircraft on the 258 radial outbound from KMOT per the IFR Low chart. It looks like my initial test in the SW121 may have been too close to the airport to make an assessment of any possible error. I’m now seeing it track outbound within 1 degree of crosstrack error and on the correct magnetic heading vs the selected CRS (expect approx a 6 degree delta).
For EHK to BCE, the IFR Low chart shows 83 and 264-180=84 exactly the same as your LNM screenshot with the added waypoint:
So as far I can see LNM is matching the chart exactly.
Also you’re actually showing 0M on the VOR for 1L8 to EHK, which is within 1 degree of the 181 on the IFR section…the 4M is coming out of the airport, referenced to the airport’s declination, not the VORs.
Ok, maybe I’m fundamentally misunderstanding the IFR charts then. I always thought that the 083 outbound from EHK which defines V293 is the 083 radial, and not the magnetic course you have to fly. And that the radial and the magnetic course are only identical if the current declination around the VOR location and the published / calibrated VOR variation are the same. If, like in this case, the actual current declination is 5 degrees different, then I would have to fly a magnetic course that is also 5 degrees different to the one on the chart.
Which all seemed to make sense to me, because when I set the VOR1 OBS to radial 083 my position on the map shows dead centered on V293, and my actual (magnetic) course flown (without any wind) was 088. And if LNM is showing 083 magnetic instead it seems wrong to me.
So you are saying the numbers on the IFR chart, between VORs that define airways, are actual magnetic headings to follow?
(Disclaimer: I’m not a real pilot, I just like poking at some of these details of the sim and digging into how this works in real life)
My understanding is the numbers on the IFR charts are the radials. That’s why the pairs don’t line up, for example the V430 I have been looking at is the 258 radial eastward from MOT, and the 81 (+180=262) radial westward from ISN, because the VORs are oriented slightly differently.
Per the LittleNavMap manual (unless you have gone into the options and checked a box to make LittleNavMap ignore VOR orientations) the magnetic course printed next to the flight plan yellow bar and in the flight plan table for flight plan legs that are ‘outbound’ from or ‘inbound’ to a VOR (which seems to require having a waypoint in the middle so the software can correctly detect that it is an outbound or inbound leg) are referenced to the orientation of the VOR radials, not compass magnetic headings. Even though they says ‘deg M’ after them, these are VOR radials. It would be nice if it printed these as ‘R’ instead of ‘M’, perhaps I will ask the author of LNM if this is possible.
On real life IFR charts, the numbers given are magnetic radials. Dial this into the OBS, and fly this course. In nil wind, it will match your magnetic heading exactly. These courses have been ‘corrected’ to account for the magnetic declination change over time at an old installation, as it’s easier to change a course number on a chart, that to re-calibrate the VOR installation every time the magnetic declination changes by a degree or more.
For these published course numbers to be correct in MSFS, the calibrated magnetic declination (not actual) used for each installation must be know, and used as the station’s reference value. I’m not sure if this is included in the default navdata, or whether it’s correctly implemented.
I think it is taking the VOR orientation into account. 50 miles out on the 258 radial of KMOT (see edited post up the thread a bit), I am ending up within 0.6 nm of ERUVE with 3 different aircraft (SW121, SR22, and VL-3) which works out to a ~0.7 degree angular error, less then we can increment CRS by.
If it was not taking into account the VOR orientation, it would be more like 7 degrees or 6 nm off.
I’m going to keep testing and see if there are any aircraft specific errors, like with the steam gauge C172.
The default MSFS nav data is incorrect. I just checked the default BGL containing EHK using Hervé Sors’ “EasyNavs” utility program, and it shows the variation is set to 11.1 degrees East, which certainly explains why the OP’s flight path was 5 degrees off.
The Navigraph parameters for EHK in their beta nav data for MSFS has the correct 1965 value of 16 degrees East.
VOR radials on published charts are never, under any circumstances, corrected to current magnetic variation. A VOR radial is not a magnetic heading - it is the number of electrical degrees that the radial is rotated from the zero degree reference radial of the VOR. The zero degree radial points to where the magnetic North Pole was located on the date the VOR was put in service, which is not necessarily where the pole is located today.
In its internal operation, a VOR receiver measures the electrical phase difference between the VOR zero degree radial, and the radial where the aircraft is currently positioned.
The number on the VOR rose on a chart associated with a specific airway is not the compass heading to fly - it is the OBS course setting to use.
To fly a specific radial, the pilot’s only task is to set the OBS to the published course, and to fly the radial (inbound or outbound) keeping the CDI needle centered. As long as those two tasks are accomplished, the aircraft’s path over the ground will follow the radial path, whether the VOR was calibrated 2 weeks ago, or two decades ago.
In the rare case that a VOR zero degree radial was calibrated recently, then (and only then) will the magnetic heading and OBS course correspond when tracking the radial. It is much more likely that the VOR calibration is quite dated, in which case the OBS course and the magnetic heading required to fly it will differ by the difference between magnetic variation today, and the variation that existed when the VOR was last calibrated.
This assumes a zero-wind situation. As a practical matter, with any amount of crosswind, there will be a wind correction angle applied that would cause the OBS course and aircraft magnetic heading to differ, even if the VOR has a recent calibration to magnetic north.
I agree with everything you have said. MSFS data is wrong, as all VORs seem calibrated/aligned to the current mag var, not the historic value at the time of installation.
The one point I disagree with is that published courses are never amended. You are 100% correct in that the published course is the number of degrees from the stations 0° reference. If, over many years, the mag var for the site’s location changes by 5°, than the magnetic radial required to draw the same track over the ground now changes by a corresponding value. Whilst the 090° radial will always be 90° offset from the reference vale of 0°, the magnetic course required to fly from A to B will change over time. Given these are the values published on IFR charts, they are amended over time to ensure the published value will still provide the same ground tracking.
I guarantee that if you viewed the 1965 charts for the above discussed navaid, the published magnetic course for airways emanating from this VOR, would be different to what they are on today’s chart.
This leads to the problems in MSFS. All navaids are aligned to current magnetic north. Therefore any published course that has been corrected over time to account for the different between the navaids installation alignment, and the sites current mag var, actually introduces an error, rather than removes it. IFR charts effectively become the source of the error as their corrections are no longer require.
If the Navigraph data aligns VORs to the sites original value, rather than the current mag var, as you suggest (I hope you are correct),than current IFR charts become correct again.
Many of them are correct, and the avionics follow them correctly, at least for the G1000, G3000, G5000, and the weird narrow vertical Garmins in the SW121.
A few high declination examples, LittleNavMap vs WxBrief:
No. They don’t re-align the VORs over time. That would require changes to the physical equipment. The IFR charts specify the VOR radials based on the current orientation of the VOR at the ends of the lines, NOT a magnetic course. The VOR 0 degree radial orientation is the same as it was whenever it was last physically adjusted - 1965 for the case of EHK.
Once the physical VOR installation is in place, any additional magnetic variation over time is irrelevant.
Many default VORS in MSFS do have the correct variation, but some such as EHK are incorrect apparently.
No, charted courses have absolutely nothing to do with magnetic heading. The two would only have corresponded the day the VOR was put into service. I have been working in the avionics field since 1974, primarily on aircraft navigation systems, but from 1990 to 1993 was a contractor for Thales electronics working as part of a crew upgrading several FAA VOR installations in the northeast and midwest. This is an area I which I have considerable hands-on professional experience.
In the case of EHK, and V293, the airway is defined as the line segment located 83 degrees clockwise from the VOR’s zero degree radial. That was true in 1965 and is still true today. The path over the ground that the airway follows is exactly the same today as it was 55 years ago. I don’t know if V293 itself existed in 1965 - it might depend on when the adjacent BCE VOR came online - and if it existed then, it might have had a different designator than V293.
But, whether it is part of a designated airway or not, the 083 radial, (and its corresponding ground path) is, and always has been, exactly 83 degrees clockwise of the VOR zero degree radial.
When you set the OBS in an aircraft to 083 degrees, the CDI needle will center when the detected phase differential between the zero degree radial and the aircraft position is 83 electrical degrees.
As I said before, the numbers on a chart are the OBS setting to use. Those numbers have absolutely nothing to do with magnetic heading. The CDI needle in the VOR indicator, combined with the OBS course selector are the only things required to fly a VOR radial. A compass or heading indicator is very helpful of course, but are not part of the VOR navigation system. If the chart numbers changed with magnetic variation changes, then they would no longer correspond to OBS settings, which would defeat the entire purpose of how a VOR is designed to work.
Here is the VFR sectional depiction of EHK, which clearly shows the angular relationship between the zero degree radial and V293. It is 83 degrees in 2020. It was 83 degrees in 1965. Neither EHK nor BCE has moved since then, so the line segment connecting the two VORs has always been 83 degrees clockwise from EHK’s zero degree radial.
All this sums it up well and is what I have been ‘guessing’ all along, and it’s great to get an authoritative confirmation.
Now, to get back one last time to the specific example of EHK (don’t intend to beat it to death but really like to fully understand) - I am using Navigraph data in MSFS, and it seems to be correct - when looking at the VOR info in LNM (which I have also updated to the same Airac cycle) it shows 16E variation and not 11E.
When I dial in 083 into the OBS in MSFS I am flying straight on V293 (as expected), and the actual magnetic heading readout is 088 (without wind). Isn’t MSFS doing the correct thing here - since today’s actual declination in this location is 11E (it changed 5 degrees since 1965), and the IFR chart is based on the 16E VOR variation, having to fly a 088 magnetic heading to follow the radial is the logical conclusion?
Reading the Navigation section of the Jeppesen Manual, it does indeed describe the magnetic course of an airway as the aggregated number of the two VOR radials at the mid point of the airway between them.
Also saying that the error in position will be so slight (in the grand scheme of things) as to not matter.
It also describes the procedure for variation, declination, chart updates etc.
To all the other comments:
You are blowing this up way out of proportion.
No, VORs don’t get inaccurate the longer they have been erected due to changes to local magnetic variation. VOR’s receive maintenance regularly like all those navaids out there and any necessary changes are updated frequently with each AIRAC. Regarding the OP’s problem, all this doesn’t even matter because he provided a situation in which his actual position was remarkably deviating from a published radial. It doesn’t matter if he took magnetic variation, wind vectors or all the fancy pseudo-scientific discoveries you posted meanwhile into account.
No matter how he got there: His CDI shows him on a specific radial which appears to be 5° off that very radial when shown on a map. Unless these maps are using a terrible projection causing such a deviation within only 15 NM distance, there is no room to assume much else than a misconfigured VOR. The North direction (maybe currently suffering from an error in the local magnetic variation database) of that VOR needs to be corrected. Then, this problem will be gone.
Edit: I noticed that the deviation is allowed to increase up to 6 degrees before the VOR station is required to receive the necessary maintenance to “reset” it to the current magnetic variation. So this could indeed be erroneous in the real world right now and we would have to wait for an additional deviation of the sixth degree before it will me corrected in real world and then (hopefully) also in the MSFS database.
Yes indeed. The current magnetic heading will be 88 degrees, and that is what you would read on your heading indicator if flying this airway in a zero wind situation. MSFS does have the current 2020 world magnetic variation map embedded into the default scenery, so this should be correct when flying in the sim.
I got my PPL in 1988, and at that time, students were taught to plot cross country flights using a sectional chart and a plotter. I presume this is still done today. A plotter is combination of a calibrated ruler and a protractor. The ruler is graduated in nautical and statute miles, specifically for use with sectional charts. The protractor is used to measure the angle between the meridians of longitude printed on the chart (which are aligned to true north), and a course line drawn on the chart in pencil during flight planning. You then add or subtract current magnetic variation to the true course to get the magnetic course that you will use while flying the course.
Many persons looking at sectional charts mistakenly assume that the zero degree north radial of the compass rose surrounding a VOR points at current magnetic north, but that is not the case - it points at where magnetic north was when the VOR was last calibrated.
In the case of my previous post with the screen capture of the sectional chart showing EHK, if you were to use the paper sectional and a plotter and extended the zero degree radial so that is crosses the adjacent 113 degree meridian of longitude (which runs true north and south), then measured the angle between the two, you would find the angle is 16 degrees - the 1965 variation.
In this case, the variation for the EHK VOR defined in the default MSFS nav data is incorrect. It has the current variation of 11 degrees, instead of the correct variation of 16 degrees that exists in the real VOR zero degree radial. This causes all the radials of that VOR to be rotated 5 degrees to the left of where they actually lie on a georeferenced chart like LNM uses, so a sim aircraft flying the airway with a centered CDI and correct course selected will be off course to the left when plotted in LNM.
Most VORs in default MSFS have the correct published variation, but some (like EHK), “slipped through the cracks” in the import process, and ended up with the current variation. I assume this happened in the process of converting the original NavBlue source data into BGL format for use in MSFS.
Either that, or the original source data was wrong. Based on some other egregious errors I have seen in various approaches supplied by NavBlue, I can’t rule out that the problem might be on their end rather than Asobo’s.
If anyone has a VOR they suspect may have the wrong variation value, please post the identifier and location, and I can check it in both default and Navigraph data files.
