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gyroblau

Lateral navigation from the flight director command bar

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Hi from Germany,

 

it looks like as when I follow the vertical flight director command bar I get off the programmed course.

 

I have the following preconditions:

  • route is programmed
  • both flight directors are switched on
  • auto throttle is on
  • VNAV and LNAV are armed
  • TO/GA is pressed during takeoff

After takeoff VNAV and LNAV become the active modes.

 

I then fly manually and follow the flight director bars. The vertical guidance from the horizontal bar is correct.

 

But the lateral guidance from the vertical bar seems not to follow the programmed course.

 

E.g. the course after takeoff makes a slight curve to the right.

I expect that when I fly straight ahead, that the vertical bar moves to the right in order to guide me to follow the course.

But the vertical bar stays in the middle or moves (for me senseless) a little bit to the left or right.

 

Only the small purple triangle (course deviation marker?) below the PFD moves to the right and gives me a hint, that I should make a right turn.

 

Do I misinterpret the function of the vertical command bar?

How do I follow the programmed lateral course while flying manually?

 

Is there a relationship (for that topic) with the PMDG setup option "AIRCRAFT" -> "EQUIPMENT" -> AFTER TAKEOFF: "Wings level" or "HDG select" ?

 

Thank a lot.

 

Carsten

 

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It should give you lateral guidance in the way you describe. The option you mention is for when you have no mode selected. The amount of lateral guidance provided by the vertical FD bar seems way too low. As a rule of thumb, if the aircraft is wings level and the FD is commanding a 30 deg bank the bar should be more or less full deflection.

 

If the AP is in control the bar should remain centred, as it does, so nothing is obviously wrong. But in manual the cues provided are too small to be usable.

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Thanks a lot for your answer, Kevin.

And I thought, I am too stupid to understand the sense of the command bar :wink: 

 

So it seems to be a small program bug in a otherwise fantastic addon aircraft.

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Cross check your FD commands with the HUD. Birdie in the cage is much more precise. The FD will remain incredibly centered. At any rate you can use the HUD of the HGS to help you clear doubts.

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So it seems to be a small program bug in a otherwise fantastic addon aircraft.

 

So far, I'm not convinced that you were interpreting the guidance properly. Please do not toss the word 'bug' around until you're absolutely sure it's something that isn't user error, and you have a ton of detail in a post for us to look at.

 

What lateral mode was being followed (displayed in the FMA)? HDG SEL? LNAV?

 

Full names in your posts, please - first and last.

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Hello Kyle,

 

like written in my first post, LNAV was the active mode:

 

Commandbars.png

 

Of course it can be, that I am not interpreting the guidance properly.

But then please help me, what I am doing wrong or what I have misunderstood.

 

Thanks a lot.

 

Carsten Buchloh

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Of course it can be, that I am not interpreting the guidance properly.
But then please help me, what I am doing wrong or what I have misunderstood.

 

It's definitely showing a left deviation here, indicating that you should make a slight turn to the left to re-capture the LNAV path.

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Also remember that the FD issues steering commands -- it is not a track deviation indicator. The cross-track error is relatively small -- only half a mile or so -- hence why it is not commanding a large bank angle.

 

Roll in a small amount of left bank and the FD bars will be centred. As you approach the LNAV path, the command bar will move out to the right slightly, commanding a small right bank to establish on the required track.

 

For small deviations, the steering commands will naturally be correspondingly small: precision is the name of the game, after all!

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Hi Guys,

 

yes it works. If you stick very precisely to the bars, than you can follow the track without any problems.

 

But maybe it is also "a little bit" true what Kevin wrote: "The amount of lateral guidance provided by the vertical FD bar seems way too low".

 

Thanks,

Carsten Buchloh

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The pic looks weird to me. I would expect more deflection with a .54nm deviation.

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Is there any factoring in of the measured winds by the FD? Also what is the expected "capture" time of the FD to the intended LNAV path? Using this example, if the pilot perfectly centers the the crosshairs how would (or rather, should) it take to close the .54 nm deviation?

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LNAV track yes. HDG SEL no. So after takeoff if you have HDG SEL and follow it and you have a crosswind you wil lbe blown off the runway extension centerline. For LNAV, use the Flght Path Vector FPV to see where that heading is taking you down the road considering the wind.

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