The last reply was good, but I have a small correction. When you're on approach with the props at 1550, they are indeed still on the governors. This is due in most part to the fact that you still have sufficient airflow over the props and that the blades do not have to go to the flight low pitch stop in order to maintain 1550. In fact, the props are on the governors up until the final power reduction to idle and flare before touchdown. If you look at the schematic for the prop system (BE1900D), the blades need to be at the low pitch stop before the solenoid can move the beta valve in order to increase oil pressure to the prop dome. So, since the props are not at the stops until the flare, the squat switch (which activates the solenoid) will have no effect on the props until that time. In our 1900's we've had a few that were misrigged and in the flare, one prop would drop off faster than the other, resulting in a yaw (sometimes very significant) just before touchdown.
Keep in mind that there is a lot more to this system and I am about as far from a mechanic as one could get, but this has been my experiences in the 1900. A few years back, Colgan pancaked a 1900 by inadvertantly lifting the levers over the gate in the flare. At that time, the props were off the governors so that is why they could go into beta.
Can any 1900 mechanics shed some more light on this?
SuperD