Autopilot Mode
 

I had to fly a King Air 200 yesterday. It was equiped with a Collins APC-65 Autopilot. It has a Mode Button called SPD-PRF. The 200 I normaly fly doesn´t have this Button and the Manual also didn´t say something about it.
All I could find out is that you can use IAS Hold or SPD PRF. I tryed it on the Ground, when you are in IAS Hold and you press SPD PRF, IAS Hold comes off and vice versa. I didn´t wanted to try it airborne. Maybe one of you Guys can help me.

Did the a/c have a FMS system? In which case it may have been the Collins equivalent of V (or vertical) nav mode. which provides a vertical profile dependant on the FMS computed data.

Yes, it got an FMS, but we don´t use it for vertical navigation.