Aircraft not following the heading

Hi everyone,

I have discovered a heading issue with FS2020.

Let's say that I am flying an aircraft VFR -- so I am adjusting the heading by myself, although I am using autopilot. Let's also assume that I am flying in perfect weather. If I set the heading to 90 degrees, for example, then once the aircraft has assumed the direction of that heading according to the avionics display in the plane, then on the VFR map, the direction is clearly less that 90 degrees -- it's somewhat less, perhaps 85 degrees. If I set the heading to 180 degrees, the plane eventually acquires about 175 degrees. In short, if I set the heading to x degrees, the plane eventually settles on (x-5) degrees.

I had been flying the Airbus A320neo when I noticed this. I then tried flying the Cessna Citation CJ4, and I obtained the same result. The direction of flight does not match the heading set on the aircraft.

Does anyone know please what is going on?

Thank you.

Stanley

Is it possible that in your location the compass variation is -5°?

Or do Garmin flight control systems take care of that?

Hi sfojimbo and everyone else,

I had thought of this.

As I understand it, however, the avionics in modern aircraft use Degrees True (not Degrees Magnetic), and so does the VFR map in FS2020.

Any thoughts on this, please, anyone?

Stanley

As I understand it, however, the avionics in modern aircraft use Degrees True (not Degrees Magnetic), and so does the VFR map in FS2020.

That would surprise me a great deal. Most things in aviation are based on magnetic directions, including runways numbers and courses, VOR layouts, etc. Maps are, of course, laid out to true north (they always have been), but typically have indications about magnetic variation, and aviation charts have many aviation facilities which are oriented magnetically, not true.

If I set the heading to 90 degrees, for example, then once the aircraft has assumed the direction of that heading according to the avionics display in the plane, then on the VFR map, the direction is clearly less that 90 degrees -- it's somewhat less, perhaps 85 degrees.

I don't have this sim, but at first I thought perhaps you had wind you didn't know about, but if the differences are, in fact, all the same # of degrees, then it may well be the difference between true and magnetic. If this is the case then, though you don't say where you are flying, you can expect that difference to change with east/west location, such as going from New York to Chicago, Chicago to Denver, Denver to San Francisco, etc.

So in New York the compass might point 10º W of true north, while in San Francisco it might be 13-14º east or true north. At 5º E you might be in El Paso or Dallas.

Don't take these figures as exact, but they'll come close as ballpark figures.

Hi sfojimbo and everyone else,

 

I had thought of this.

 

As I understand it, however, the avionics in modern aircraft use Degrees True (not Degrees Magnetic), and so does the VFR map in FS2020.

 

Any thoughts on this, please, anyone?

 

Stanley

Heading and Direction are two separate things.

Do you know the difference?

Hi mallcott and everyone else,

I guess that I don't know the difference. Here is what I understand to be the case:

The course is the direction that you set your aircraft to take using a flight plan or using the heading bug. Is that correct?

The heading is the direction in which the nose of the aircraft is pointed. Is that correct?

The bearing is the direction that the aircraft is actually taking at the moment. Is that correct?

I am very curious to know the answer to the questions that I just posed.

But also, to nail down the issue of true versus magnetic degrees, doesn't a GPS unit use true degrees? I am talking about the GPS unit in one's vehicle, as well as the GPS unit in an aircraft.

Thank you.

Stanley

The course is the direction that you set your aircraft to take using a flight plan or using the heading bug. Is that correct?

That is your desired course. The actual course is the path you are actually traveling. It's direction is normally referenced to magnetic. Note that this becomes a failsafe, too, since an aircraft is required to have a mag compass, which still works even if all electronics/avionics fail.

The heading is the direction in which the nose of the aircraft is pointed. Is that correct?

Yes, that's right, and it can be stated either as true or as magnetic heading, but in aviation navigation it WILL be magnetic.

The bearing is the direction that the aircraft is actually taking at the moment. Is that correct?

No. The bearing is the direction from something to something, usually with the nose being 0º, so the bearing from the aircraft to an airport off to the side might be 45º, but changing as you travel. If the bearing is at 0º then you're headed straight for the someplace. The bearing is usually referenced to where you are at the moment (changing as you move), although if someone else took a bearing on you then it would be referenced to them.

But also, to nail down the issue of true versus magnetic degrees, doesn't a GPS unit use true degrees? I am talking about the GPS unit in one's vehicle, as well as the GPS unit in an aircraft.

Yup. Nope. Maybe. Are you aware that the N/E/S/W indicators on a car's dash are magnetic? They are readouts of an electronic compass.

Actually, the GPS (car, aircraft, handheld) knows about the magnetic variation (magvar) where you are, so it knows about both magnetic and true north, and technically the GPS actually uses geographic (true) north measured using WGS-84, but can display courses either related to true or to magnetic. But that's all internal. What it displays depends on what it is designed to display. In a car GPS, I rarely see any reference to degrees of heading at all, usually it displays a road, turn left/right, take ramp, etc. If it displays your direction of travel (heading) then it's magnetic in the ones I've seen.

In aviation (hiking, too), navigation is normally referenced to magnetic north, though true can be displayed if the GPS internal software allows for that, but it might only be shown in certain modes -- depends on the unit. But compasses and gyroscopic heading indicators (DG) are referenced to magnetic (even on a moving map display, on a PFD, etc.) since they are basically a stable compass (doesn't bounce around), VOR radials are magnetic, runways are magnetic, and if you talk to ATC then any direction they mention will be magnetic, plus they expect you to reference magnetic when talking to them.

If you suddenly start referencing everything relative to true north, you'll be out of step with the rest of aviation.

Don't get me wrong, true north might be nice to know, and often when plotting courses, etc., on a paper map you will probably use true initially, then convert it to magnetic for use in flight.

Aviation navigation uses magnetic.

Hi Larry,

Wow! Thank you very much. I will study this and absorb everything you told me.

Extremely helpful. You are most knowledgeable.

So then this question just popped into my mind. The VFR map that we see in FS2020. Is that using true or magnetic degrees?

Stanley

Stanley, it occurs to me that you could try a couple of things that will show what type of directional reference that you are using.

Go sit on a runway, with the aircraft aligned with the runway. Look up that runway direction on Airnav or some such -- they are numbered to the nearest 10º, so runway 06 is somewhere near 060º, that is between 056º and 65º. Airnav (or most any approach plate for that runway) can show the exact heading for that runway. Then see what you read on your instrument panel for a heading.

Another thing you can do is to fly on the east coast, noting the difference in heading indications, then fly on the west coast and note the differences. Then compare those differences to the isogonic lines (that is, to the magnetic variation) for each location. I suspect you'll find that the heading differences will not be the same between the two coasts.