Autopilot Flight Change not holding selected airspeed

[MSFS 2020] Questions & Community Discussions Aircraft
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I’ve encountered an issue whereby the autopilot flight change (IAS hold) mode is not correctly holding the selected airspeed but some other airspeed instead, for example it might be commanded to hold 250 KIAS but instead holds 220 KIAS. This isn’t an issue that I’ve encountered on the other 7-10 aircraft that I’ve worked on.

The issue is consistent throughout the entire airspeed envelope (e.g. 180 to 330 KIAS) and the autopilot does a good job of holding the airspeed it settles on, despite it not being the airspeed that I’ve commanded, so it doesn’t seem to be PID related.

The airspeed it holds is always lower than the commanded airspeed but apart from that I’m struggling to see any relationship between the commanded airspeed and the airspeed actually being held. I initially suspected it might be holding a Mach speed instead but that’s not the case.

As far as I can tell there is no ‘managed’ autopilot/autothrottle logic in use and the autothrottle airspeed hold is working fine.

Has anyone else come across this issue before? Any suggestions that I can try?

IAS

Thanks in advance,
Martyn

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@FlyingRaccoon

I have been trying to solve why we can’t hold autotpilot MACH in Flight Level Change, but we can in IAS.
I have been using the AP_MANAGED_SPEED_IN_MACH_TOGGLE. Does this in fact work or do I need to do more. I have confirmed in simvars this is on.

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Working now. For those who need help you need to set these.

AP_MANAGED_SPEED_IN_MACH_SET to toggle the mode.
AP_MACH_VAR_SET to set the mach speed
AP_SPD_VAR_SET to set the ias speed

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