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FLJeff337

VOR Radial Not Aligned To Real World

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All:

I'm having a problem with a VOR whereby the radials depicted on the chart don't match the current sectional.

Before describing my problem, I want to list the current navaid updates in use, as well as the sectional being referenced

- Hervé Sors - World Navaids Package v. 7.43 (AIRAC Cycle 1607 - effective June 23, 2016)
- Hervé Sors - Updated Magvar data (current as of 2016)
- Current Jacksonville sectional (97th ed., valid from Feb 4, 2016 thru Aug 18,2016)

The VOR in question (and the only one I've specifically looked into) is the Melbourne, FL VOR (MLB) at Melbourne Intl (KMLB); the variation for this VOR (in real life) is current as of 2015 (7oW), and matches the variation of this area (also 7oW).

I realized something was wrong when, after selecting and flying the 270 radial outbound (as to stay clear of Orlando's class B airspace), my course didn't match what was shown on the sectional. In fact, my actual course was what would be expected if I flew the 275o radial (taking me over Cypress Lake, and just into KMCO's Class B airspace, which I wanted to avoid); FSX's flight analysis confirms a heading of 275o when flying the FSX MLB 270o radial.

I double checked this by figuring out my expected no-wind heading from MLB to my desired waypoint (which would have me overflying the lake just to the southwest of Cypress Lake), and found that, with a course of 263o, plus 7 degrees to account for the magnetic variation, my no-wind heading should be 270o, which agrees with the 270o radial of the MLB VOR (which remember, is current as far as variation goes).

I even used Hervé's BGL Navaids Direct Editor to inspect the MLB VOR, and saw all information (including Lat/Long and variation) was correct and current.

So my question is, what's causing this discrepancy (even with up to date navaid/mag var info), and is there any way to adjust it.

I'm including two screenshots that illustrate this problem. The first one (excerpted from Skyvector) shows the route from MLB to my desired location, and confirms that the 270o radial is the correct radial to fly.The second one shows FSX's flight analysis with two routes shown: one flying a heading of 270o (which is correct), and another showing the route when following the FSX MLB 270o radial (which is incorrect, and would be closer to the 275o radial in real life).

Any help would be appreciated.

Thanks,

 

Jeff

MLB_VORSkyvector.jpg

 

 

MLB_FSXFlightAnalysis.jpg

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It's a complicated subject when you drill into it - and I've also noticed that GPS/SkyVector and the onboard VOR equipment virtually never agree exactly.

There's a post from Pilot Edge forum that delves into it - the answer or part of it at least might be here.

http://forums.pilotedge.net/viewtopic.php?f=3&t=3956&p=25196

Also VOR radials in general are subject to various inaccuries, siting errors due the location of the equipent 1.5 degrees from memory - but these exams were a long time ago, on-board equipment errors, 3 degrees from memory, plus pilot in-exactitude, could come to 5 degrees in total.

This is why airways were 10 miles wide - before GPS, navigation wasn't exact.

Eugene

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I figured out where the discrepancy came from....

 

While the default VORs had been updated to their current magvar values (thanks to Hervé's navaid update), a number of my add-on airports had their own MLB VORs as part of the scenery, and the magvar values for these are the older 2W value (which was discovered when I opened the airports in Airport Design Editor, went to the Navaids list, and examined the MLB VOR included with the scenery).

 

By either disabling the add-on airport, or by editing the magvar value for the VOR in ADE to the correct, current value, I was able to resolve the problem I was having.

 

Apologies for resurrecting an old thread, but I thought this discovery may be helpful for others who may be having the same problem I was, but not able to figure out why.

 

- Jeff

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