When flying the Dash-8, I use the autopilot (without using the FMC). It seems that I cannot set both Altitude Hold and IAS at the same time.For example, I have altitude hold set but later set IAS. Then the IAS setting kicks in but it seems to override the altitude hold and the plane starts to descend? Is this a limitation of the autopilot, something I am doing wrong, or a bug in the program? How do I set both altitude hold and IAS at the same time?

HiThe bottom line is that you need to manually adjust power settings.There is no autothrottle per se in the PSS 8

Ron is partially correct. IAS is a vertical hold function in this aircaft, and many other turboprops. There is no autothrottle, as Ron notes, the only way the aircraft has of maintaining IAS is by pitching up or down. So, by setting a given power setting you can get the aircraft to climb or descend at a fixed speed, but variable rate. As you can't set IAS (with variable rate of climb) and alt (with a fixed rate of lcimb) at the same time you must choose one of the two modes. MSFS default aircraft lack this facility, which is curious as they separated the autothrottle from the autopilot in FS2002, the main justification for which would be to provide a correct IAS mode!Most t/p manuals include fixed IAS settings for climb and descent, and these will be in conjunction with specific power settings. The rate of climb is less important.Hope this helpsChasW

Thank you for this useful information. Looks like I will have to manually adjust the power.