Healy,
SOP on the 146 is to deploy the Airbrake just prior to touchdown to minimise landing roll. The airbrake is independant of the lift spoilers, though both are controlled by the same lever.
The Airbrake lever is on the left side of the centre pedestal. Moving the lever aft causes hydraulic pressure from the Green system to open the Airbrake. It is infinitely controlable between fully closed and fully open, and there is no speed restriction on its use, though as with most drag devices, that faster one is the more effective it is.
When the Airbrake lever is in the fully open position, usually resting against a "gate", once wheels are on the ground further aft movement of only a few centimetres will deploy the lift spoilers.
The lift spoilers are inturn controlled by squat switches to prevent them from deploying in the air, so it would be feasable to select lift spoilers in the air and have them automatically deploy on touchdown, though this is contrary to the AFM and company SOP.
The Airbrake control lever is often fondly referred to at the PCL. The Pilot Correction Lever, it's a wonderful device for correcting botched descent profiles, or, allowing 250 KIAS to inside 10nm from touchdown then slowdown reconfigure and land.