Why does my Approach show up as "Unavailable"?

Sometimes an approach will appear on the screen with "Unavail" listed by it, or possibly grayed out.  This is not a database problem. The approach is there, but there is something going on in the background that it is "downgrading" the approach to unavailable. 

Possible Causes for this are:

• The approach is for Baro-VNAV equipped avionics only, and the avionics doesn't have Baro-VNAV capability.

• The avionics have not yet achieved a full and complete WAAS signal. This can happen if you are on the ground with limited GPS signal.