The Q400 is designed with three modes of spoiler operation:

Flight: The spoilers operate in proportion with the up aileron to provide roll control. When one turns the control wheel, it operates both the aileron and spoiler. There are two sets of spoilers, the inboard and outboard spoilers. The outboard spoilers are disabled above 170 KIAS and re-enabled below 165 KIAS.

Ground: Each spoiler has a set "lift-dump" valves that cause the spoilers to fully extend when the following conditions are met:

-Flight/Taxi Switch is in the FLIGHT position
-Both Power levers are less than Flight Idle + 12 degrees
-Main Landing Gear are on the ground
-Hydraulic Pressure is available