For approaches, the surveyor surveys the area and establishes an
Obstacle Clearance Height (OCH) for the approach.
The regulator then determines an appropriate overall
System Minima for each type of approach - this is the minimum altitude that an operator may authorise their crews to descend to on that type of approach.
The operator then looks at their training program, equipment and experience in an area of operations and determines the authorised minima for each approach (which in the vast majority of cases is the same as the greater of the system minima/OCH - and this is the number Jeppesen place on their charts, unless you have an operator-specific chart).
The Commander then sets the minimum for the approach on the day. This is the charted number in the vast majority of cases, but the commander has the right to say (for example) "On
today's approach, with this weather, this terrain and these MELs, we shall add 200 feet to the published minima before making a missed approach and diverting."
From EU-OPS (available on-line at:
EU-OPS):
Appendix 1 (Old) to OPS 1.430
Aerodrome operating minima
2. Minimum descent height. An operator must ensure that the minimum descent height for a non-precision approach is not lower than either:
(i) The OCH/OCL for the category of aeroplane; or
(ii) The system minimum.
3. Visual reference. A pilot may not continue an approach below MDA/MDH unless at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:
(i) elements of the approach light system;
(ii) the threshold;
(iii) the threshold markings;
(iv) the threshold lights;
(v) the threshold identification lights;
(vi) the visual glide slope indicator;
(vii) the touchdown zone or touchdown zone markings;
(viii) the touchdown zone lights;
(ix) runway edge lights; or
(x) other visual references accepted by the Authority.
The 50' addition to the MDA referred to above is applied by the operator (and is a pseudo standard) as part of step three above. The
regulatory requirement is both to "not continue an approach below" AND an "operator must ensure that the minimum descent height for a non-precision approach is not lower than" (which is why most operators specify 50' addition)
however there is no regulatory reference which specifies that "50 feet" shall be used.
You are, of course, legally bound to follow your OPS manual procedures.