Whereas at DA a decision is made (which will involve the aeroplane descending briefly below DA before go-around is achieved), as we all know, at MDA the aeroplane must not descend further until the appropriate visual references are achieved.
So for those youngsters not trained to fly level at MDA and who therefore treat MDA as DA, an extra factor must be built in to ensure that the aeroplane does not descend below MDA when go-around is initiated. Hence for those who insist on using the DA technique on a non-precision approach, an extra 50 ft at least must be added to MDA to compensate.
Trainig and practice are needed to fly a 'dive and drive' - but commercial pressures rarely allow such luxuries these days.
[ 01 December 2001: Message edited by: BEagle ]