xmp,
The HUD CAT IIIa capability on a CRJ is strictly for manual flight only - the Autopilot (CAT II if you want to use it) is only used to get you to below 2000 ft agl when AIII mode is selected on the HGS. The pilot must disconnect & fly manually by 650ft agl or he gets an Approach Warning (= Go Around). Monitoring is carried out both inside the HGC and by the Co-Pilot checking pilot performance on his PFD. Again any failures or not keeping the aircraft within limits ("making donuts") and you'll get an Approach Warning & MUST do an immediate GA.
SLB