Hi Guys,, interesting debate.
Here is how a NPA is flown in our company:
We use a concept of CANPA = Constant Angle Non Presicion Approach.
The way the approach is constructed is basically taken from the CAA own plates and prosedures as they comply with Pans-Ops.
The way it is done, is that from the Mapt a constant angle line is drawn from it and outwards towards your DP = Descend Point (Now going backwards. This line is designed to touch the point that has the highest ALT/DIST ratio therfore it will never go below any mandatory altitudes. This means that your descend point on a CANPA approach can be moved forward (Closer to the THR). The way it is flown is that on our approach plate there is calculated an altitude for every mile after the descend point. Our Company regulations states that if you are below 150 ft. on a non-mandatory altitude a missed appr. must be made. A tolerance of +150 / -0 is tolerated on an mandatory altitude. When you reach your MDA this altitude is to be regarded as a DP so if no contact is made then missed approach. (There is nothing other than company regulations in our company that prohibits you from flying level at MDA to your Mapt). On our plate there is also a speed vs ROD table given, so you just set that VS for the autopilot and tracks the radial or NDB whatever by using either HDG or NAV (Radial tracking APP). Crew Coordination is so that PNF=Pilot not flying calls applicable CANPA profile altitudes and the deviation for every mile. A hundered feet before MDA/DP PNF looks out and calls runway insight or if no call is made before MDA/DP the Missed.
It works fine as long as you can consentrate on your flying during this approach. Therefore it is a good rule of thumb to be fully configured and completed all checklists before DP. I mean an approach at 160 kts or more requires a ROD of app. 950 (933) ft/min on a 3,5 degree slope things happends fast if one pilot is flying and the other one reading
2Daddies and others:
Seems to be a little confusion about the terms MDA DA DP Mapt DH.
According to design criteria for approaches used in Europe (Pans-Ops 4) also refered to as old Pans-Ops, not correct in my opinion as 1,2,3 are also old and even older
)
MDA = Minimum Descend Altitude is the term for the Minimum altitude you are allowed to descend to on a Non-presicion Approach.
Mapt = Missed Approach Point is the point (Either a distance from a source or the time flown from passing a source NDB/VOR during the initial approach. This is usually also your FAP=Final Approach Fix) At which the Missed Approach segment of your approach starts and is therefore the point at which you would have to start your missed approach.
Mapt and MDA together constitutes a DP = Desicion Point. As the point at latest a desicion to either continue or abbandon the approach has to be made. These are the terms used for NPA's
DH = Desicion Heigh is the height above the ground from where you must have made a desicion to continue or go-around. This is also a DP as DH is used on a Presicion Approach thereby giving a three dimentional fix from where the missed approach segment starts. As DH is the minimum height at which an approach can continue down to it is also the point at which your DA is calculated (Field elevation + DH = DA) This height is minimum 200 ft on a CAT 1 approach and minimum 100 Cat 2 and so on down to CAT 3c minima of 0 ft.
DA = explained
Hope this clears up the confusion on the terms.
Happy landings!!