I personally doubt that the Q400 autopilot can fly a single-engine approach without any difficulties as the Q400 requires rudder trim changes for any power change and the autopilot simply cannot trim the rudder. Maybe already posted somewhere here, but it really is a pity that Bombardier/Sextant did not add some kind of auto-trim for power changes or a powerful yaw damper.
AFAIK even WW2 Messerschmitts had something like that.....
Dunno, but our good ol' 737 classic needs trim changes for power changes as well (or you have to adjust pressure on the rudder pedals, your choice). Still i can fly single engine approaches down to 150ft although our company encourage us to fly most of it manually, just ot be prepared for the inevitable flight director/autopilot fail on go-around
