I am reading this thread as a result of studying non-precision approach practices, because of the UPS BHM accident in Aug, 2013, where they hit obstacles after descending visually below the MDA to attempt to land.
Any my US -121 airline, for a non-precision approach (which we normally fly a CDMA), if there is a published glidepath on the approach chart (jeppesen) and a published glidepath in our FMS database, we are to set the MDA as the DA. Consequently, when going around we will go below the MDA.
If there is NOT a published glidepath, then we must add 50' to the MDA, which should keep up as above the MDA if we go around.