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jmdriskell

Magnetic Heading Errors

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I have a problem with a number of flight planners generating magnetic headings that are off from what's shown on an actual chart.  I created a simple flight plan from KWMH to KWMH in Washington State which I use for practice navigation and ILS approaches.  I've used both Flight Sim Commander and Professional Flight Planner to come up with the following course.  I also plotted the same course on the latest Seattle Sectional.  The differences vary too much for my liking.  Incidentally, I have applied Hervé Sors latest correction for 1/1/2020 to my FSX-SE installation.  Here's what I come up with:

From        To     Planner Heading     Chart Heading

KMWH      ETH   323°                         318°

EPH          EAT   258°                         252°

EAT          ELN   189°                         189°

ELN          YKM  164°                         158°

YKM         PSC   093°                         108°

I've noticed variations in courses in other locations around the world.  I'd appreciate anyone's insight into this problem. 

BTW, FSTramp seems to display the correct headings when I activate it during the flight.

 

Thanks in advance,

 

Jim Driskell


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James M Driskell, Maj USMC (Ret)

 

 

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The flight planner headings are correct. They are based on current magnetic variation for each waypoint.

If you are a r/w pilot, you may be very surprised to learn that the magnetic north radials of many VORs are often years out of date, (and therefore many degrees different than current magnetic north) and the actual magnetic headings of many victor and jet airways on sectionals and IFR enroute charts are not the magnetic headings depicted on the charts!

The reason is that the published radial courses are not compass headings, they are OBS settings, and that is something that even many highly experienced pilots may not be aware of.

Here is what is going on:

The zero degree radial of the Ephrata VOR (EPH) was last calibrated to local magnetic north in 1975. The variation has changed significantly since then. The actual variation of EPH is 16E but the VOR variation is based on 21E, (which was what it was in 1975). 

On the other hand, the Wenatchee VOR was calibrated just a few months ago in March of 2020, and its zero degree radial is set to the correct current variation of 15E. 

You can see the VOR variation disparity right on your sectional. EPH and EAT are only 22 miles apart, and V120 connects the two. V120 is a straight line. Note that the outbound course reference of V120 at EPH is 252 degrees.

Since the two VORs are so close, you would assume that the outbound V120 radial at EAT would be the exact reciprocal yes?

252-180 = 72 degrees, but note that the actual V120 radial at EAT is 77 degrees - 5 degrees more than expected. That is because EPH is calibrated to 1975 variation, and EAT is calibrated to 2020 variation.

Next leg: EAT to ELN

Since the variation of EAT is current, the planner and chart are both showing 189 degrees for that leg, but note again the outbound radial of V25 at ELN. The chart shows 3 degrees, but 189-180 is 9 degrees. ELN VOR’s north reference is based on the variation of 21E that existed in 1980. The current variation is 15E.

1975 might seem like a long time, but some VORs were last calibrated to magnetic north a lot farther in the past than that. Albuquerque VOR (ABQ) magnetic north is based on 1965 variation of 13E. The current 2020 variation at Albuquerque is 8E!

So, you may be asking: “You mean the official current published FAA charts I use for VFR and IFR navigation are wrong??

The answer (in a manner of speaking): “it depends on what the meaning of ‘is’ is.”

From a technical standpoint, it really does not matter, strangely enough. In the case of EPH VOR, even though the zero degree radial is offset almost 6 degrees from current magnetic north, a VOR receiver does not know (or care) what actual magnetic north is. From the receiver’s “viewpoint” the 252 degree radial is simply the point in space where the phase difference between the VOR’s north reference signal and the rotating 30 Hz signal is exactly 252 electrical degrees. 

Or to put it another way, the path over the ground that the VOR radial describes does not change even though the magnetic zero degree radial of the VOR is no longer pointing at magnetic north. If you start at EPH, set the OBS to 252, and fly outbound keeping the CDI needle centered, you will soon pass almost directly over the town of Soap Lake. That would have been true in 1975, and is still true today.

From a pilot’s perspective, as long as you set the OBS for a particular airway to the published course setting shown on a sectional or enroute chart VOR rose, and fly the airway with a centered CDI needle, you are assured of following the airway’s path over the ground. Since real world VOR tracking is usually done with a certain amount of wind correction angle, you’d be surprised how many pilots may fly VOR to VOR for years without ever noticing that the published VOR radial, and the compass heading required to maintain that radial often don’t quite “jibe”.

You may wonder why the FAA doesn’t re-calibrate particular VOR’s magnetic north more often, but as a practical matter, doing so is a massively complicated undertaking because of the changes that would result in every airway and procedure that references that VOR.

If the VOR magnetic north reference is changed, the published charted OBS course reference of every victor and jet airway connected to that VOR would have to be revised, as would every airway intersection, and every instrument approach procedure that references that VOR in any context (other than pure DME distance references). Then, every one of those airways and approaches would have to be flown by FAA flight check aircraft, and recertified. It is a long, complex process, and the VOR would have to remain out of service during the entire time.

Edited by JRBarrett
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Jim Barrett

Licensed Airframe & Powerplant Mechanic, Avionics, Electrical & Air Data Systems Specialist. Qualified on: Falcon 900, CRJ-200, Dornier 328-100, Hawker 850XP and 1000, Lear 35, 45, 55 and 60, Gulfstream IV and 550, Embraer 135, Beech Premiere and 400A, MD-80.

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Wow!  Thanks for the extensive and revealing review of this problem.  I am a r/w pilot but not current in anything.  I always try to fly my sim flights as accurately as possible so that's why I noticed the discrepancy.  Your explanation of this problem necessitates much more study on my part.  And considering that the magnetic north pole is shifting more quickly now than in the past, the chart directions will continue to change more and more.  For instance, KMWH runway 32 is actually about 327 plus or minus degrees instead of the published 324. 

I recently had a simulated flight into Thule, Greenland BGTL.  Magnetic headings in this region are really unreliable.

Again, thanks for the detailed explanation.

Jim Driskell

Edited by jmdriskell

Boeing777_Banner_Pilot.jpg

James M Driskell, Maj USMC (Ret)

 

 

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1 hour ago, jmdriskell said:

Wow!  Thanks for the extensive and revealing review of this problem.  I am a r/w pilot but not current in anything.  I always try to fly my sim flights as accurately as possible so that's why I noticed the discrepancy.  Your explanation of this problem necessitates much more study on my part.  And considering that the magnetic north pole is shifting more quickly now than in the past, the chart directions will continue to change more and more.  For instance, KMWH runway 32 is actually about 327 plus or minus degrees instead of the published 324. 

I recently had a simulated flight into Thule, Greenland BGTL.  Magnetic headings in this region are really unreliable.

Again, thanks for the detailed explanation.

Jim Driskell

You’re welcome!  Many pilots were trained that VOR radials represent magnetic headings, but they actually represent the rotational angle from a specific VOR’s zero degree reference radial, which may (or may not) correspond to the actual magnetic north at that VOR.

As long as you set your OBS to the published course, and keep the needle centered, it will all work as designed!

More and more VORs are being decommissioned every year. I can understand the FAA’s desire to move fully to GPS as the primary means of navigation in the national airspace system. It’s much more accurate and easier to maintain. Many VOR transmitters are so old that it is very difficult to obtain repair parts anymore.

But, I always worry about the unpredictable “100-year solar flare” that might seriously disrupt or even destroy the GPS satellite constellation. Not sure it is wise for the FAA to put all their eggs in one basket.

Edited by JRBarrett
  • Like 1

Jim Barrett

Licensed Airframe & Powerplant Mechanic, Avionics, Electrical & Air Data Systems Specialist. Qualified on: Falcon 900, CRJ-200, Dornier 328-100, Hawker 850XP and 1000, Lear 35, 45, 55 and 60, Gulfstream IV and 550, Embraer 135, Beech Premiere and 400A, MD-80.

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I agree completely with you about putting all our navigation eggs in one basket.  I recently read somewhere about a possible resurgence of LORAN but I don't know if the idea has any legs.  In addition, "GPS is facing a major interference threat from a 5G network approved by the Federal Communications Commission, US military officials told Congress in a hearing ..."  So it's incumbent that aviators carry some of the old tricks in their tool box in order to get from point a to point b.  I understand that some manufacturers are doing away with the whiskey compass in favor of  an electronic one that has battery backup.  What could go wrong with this idea.  When in doubt, follow the whiskey compass like the SR-71 crew that experience a power failure while on a mission somewhere over southeast Asia.  They flew the bird back to Kadina with it as their guide.

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James M Driskell, Maj USMC (Ret)

 

 

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