Autopilot Flight Change not holding selected airspeed

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?


Thanks in advance,