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mSparks43 / 747-400

A Boeing 747-400 aircraft for X-Plane 11 & 12
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[AP] Flickering SPD Bug during VNAV CRZ #777

Open oMrSmith opened 2 years ago

oMrSmith commented 2 years ago

During CRZ VNAV PTH can't decide on target mach speed causing the speed bug to flicker and the throttle to move erraticaly:

https://user-images.githubusercontent.com/78870770/163606206-d1fb0c3e-7f77-4f25-99b0-50f284ca59d8.mp4

oMrSmith commented 2 years ago

What's interesting:

If you select manual speed and manual speed is still set to mach, the speed bug still flickers, but then if you switch over to knots, it goes away although it's the same speed.

mSparks43 commented 2 years ago

this is "kinda" a known issue. The cruise speed is set above the max safe speed, the protection system is setting it to a safe speed, but that works in kts, the VNAV system is working in mach and doesn't know the safe speed and it oscillates between set speed and safe speed.

The workaround is "dont do that".

oMrSmith commented 2 years ago

"dont do that" :D But the plane is doing it automatically... Wouldn't it be possible to have VNAV set a CRZ SPD that does not exceed the MAX safe speed?

mSparks43 commented 2 years ago

"dont do that" :D But the plane is doing it automatically... Wouldn't it be possible to have VNAV set a CRZ SPD that does not exceed the MAX safe speed?

Yes, but it needs either mach converting to kts or a better way of detecting that "it tried that already", neither of which were that simple compared to just not trying to set a mach speed faster than max safe speed.

Also dont actually know how it should behave - not found a reference for this case.

oMrSmith commented 2 years ago

@mSparks43 what do you think: Would it be possible to simply bypass the switch over to mach speed for now, as it only causes trouble without giving any benefit?

oMrSmith commented 2 years ago

It seems like the flickering SPD Bug only happens with higher CI values... I just flew my testroute form LGMK to LGAV with the CI set to 300 and the mach speed wasn't set above safe speed...