suddenWinds caution with the interchange of MDA and DA. Whilst this is OK procedurally, the definition of each and the resultant obstacle clearances may not be the same.
The problem of the visual minima not correlating with the required vertical flight path at MDA was a factor in the Avro RJ CFIT accident at Zurich, i.e. when on a nominal 3 deg path the runway could not be seen in the procedure visibility minima of 2000m; for the 900ft MDA, 4k vis was required. The Zurich procedure was modified and the principle was to be applied universally. However, I do not have evidence of any action, thus operators are recommended to publish their own (increased) visibility minima to provide a reasonable chance of seeing the runway at MDA.
Don’t kid yourself that a slightly steeper approach will be OK, the situation at Zurich resulted in a flight path of 6 deg as opposed to one nearer 3 deg. (Info from Presentation ‘Reducing CFIT Risk’ FSF European Aviation Safety Seminar circa 2003).
A pedantic point (maybe), but VDP should not be inferred as being at MDA. On a non precision approach (NPA), you have little or no control of the point along the approach path when you reach MDA, thus the range to the runway is unknown (thus use time to MAP). Some NPAs use DME or allow RNAV, but these are not a substitute for a precision approach (and fraught with opportunities for error).
This point is the main reason why altitude range-checks (VS/timing) are an essential series of checks during NPAs, and why the altitude component must be checked first. Altitude is the dominant limit (if you fly to a distance from a runway without checking altitude, then there is no protection from terrain
Celebrating TAWS ‘Saves’: But lessons still to be learnt. ).
VKM MDA is an
altitude which provides the required obstacle clearance during a non precision approach. The MAP is normally a
location along the approach track.
It has been established that level flight at MDA increases the risk of operation thus the concept of flying a stabilized approach was introduced which also includes commencing a GA when at or just above MDA (CANPA). (GA is also flown from the MAP if it is reached before MDA.) Unless directed otherwise the approach track should be maintained and the MDA position should be over-flown during the GA.
hawk37 my understanding is that the PANS OPS height loss values are used in procedure design, which I believe looks at absolute values; whereas the JAA discussion on height loss during GA from MDA related to the collision risk and thus a ‘50ft height loss’ not an absolute value – more of an alleviating margin.