MDA & MAP

One thing to really pay attention to on any Instrument, CFII or ATP ride is the MDA.  The PTS states (in part) you must maintain the MDA, when reached, within +100 feet, −0 feet to the MAP until told to execute a streight-in or circling approach when instructed by the examiner.

I've recently had a few issues with this.  One applicant missed a step-down fix and descended 400 below the segment MDA another blew right threw the MDA and I stopped the descent about 100 feet above the corn.  On a real IFR flight descending prematurely could be deadly.  On a check ride it will result in with a Notice of Disapproval.

Being able to identify the MAP on approach is another important subject.  How does your GPS tell you you're at the MAP?  How do you determine the MAP on a LOC approach?  Is it Distance, Time, or something else?  How do you know? If you wish to start the Missed approach before the MAP, what limitations must be observed?  How do you get established on a Missed Approach after attempting to circle to another runway?