At work (European airline) we used to add 50’ for approaches that had an ‘MDA’. I think it was aobut 2 years ago now that this requirement was removed. I can not reference any change to regulation for this, but it has obviously been approved by the regulator. Our charts have also had all reference to ‘MDA’ removed and now we just have a ‘DA’ for everything, keeping in mind that as Part-CAT we are not allowed to dive and drive. Part-CAT does say the following, from CAT.OP.MPA.115 and it’s associated AMCs should anyone be interested:
This DA/H should take into account any add-on to the published minima as identified by the operator’s management system and should be specified in the OM (aerodrome operating minima).
Here is some information from part NCO
NCO.OP.111 Aerodrome operating minima – NPA, APV, CAT I operations
Regulation (EU) No 800/2013
(a) The decision height (DH) to be used for a non-precision approach (NPA) flown with the continuous descent final approach (CDFA) technique, approach procedure with vertical guidance (APV) or category I (CAT I) operation shall not be lower than the highest of:
(1) the minimum height to which the approach aid can be used without the required visual reference;
(2) the obstacle clearance height (OCH) for the category of aircraft;
(3) the published approach procedure DH where applicable;
(4) the system minimum specified in Table 1; or
(5) the minimum DH specified in the AFM or equivalent document, if stated.
(b) The minimum descent height (MDH) for an NPA operation flown without the CDFA technique shall not be lower than the highest of:
(1) the OCH for the category of aircraft;
(2) the system minimum specified in Table 1; or
(3) the minimum MDH specified in the AFM, if stated.
AMC1 NCO.OP.111 Aerodrome operating minima – NPA, APV, CAT I operations
NPA FLOWN WITH THE CDFA TECHNIQUE
When flying a non-precision approach operation using the CDFA technique, the pilot-in-command should ensure that when executing a missed approach, the initiation of the go-around is done at or above the DA/H to avoid flying below the MDA/H.
Airborne_Again wrote:
I’m pretty sure those waypoints are not part of the actual approach. Jeppesen uses them for the “overlay” approach in their nav databases and they are charted for the benefit of pilots who are using those databases.
But how you cross-check distances on plate against the actual situation and instruments in the aircraft?
NCYankee wrote:
I also attached the approach chart
Just looked again to 8A7 approach, any reason why MDA is provided on two altimeter settings and 40ft OCH delta? can you fly there on a 3rd altimeter setting? 
I understand in US if no local altimeter setting is available at destination airport, you need the one by facility designated on approach chart but I did not expect it makes any difference to DA/MDA/DDA even if taken from two sources? how this is handled in TERPS: historical pressure/temperature corrections on specific places referred by the plates? or just OCH margins based on distance from local aerodrome?
40ft you are looking for 8nm distance between Smiths Reynolds and Davidson & Co 
ICAO PANS/OPS,
- For 2D-LNAV minima, the OCA/H increased at 0.8m/km or 5ft/nm if no local QNH within 5nm
- For LNAV/VNAV minima, no OCA/H adjustment to be made if no local QNH
But how you cross-check distances on plate against the actual situation and instruments in the aircraft?
My take on that approach: you either have an approach-approved GPS (and use the overlay) or you have not (i.e. only an ADF, nothing else)
In the first case, you can use the GPS distance from the threshold to do the CDFA.
In the latter case, you turn inbound after the procedure turn, and as soon as established on the final approach track, you descend to the MDA (and go missed after reaching the NDB again). Since you don‘t have the distance from the threshold, you can‘t do the CDFA (no way to monitor it).
Ibra wrote:
Just looked again to 8A7 approach, any reason why MDA is provided on two altimeter settings and 40ft OCH delta? can you fly there on a 3rd altimeter setting?
Remote altimeter sources have distance and elevation taken into consideration when a local altimeter source is not available. It is all described in gory detail in 8260.3E:
(1)Where intervening terrain does not adversely influence atmospheric pressurepatterns, use Formula 3-2-3 to compute the basic RASS adjustment in feet (see Figure 3-2-2).
Formula 3-2-3. Basic RASS adjustment (no intervening terrain)
Adjustments = 2.30×𝐷𝑟+0.14×𝐸1
Where:
Dr = Horizontal dist (NM) altimeter source to ARP/HRP*
E1 = Elevation differential (feet) between RASS elevation and airport/heliport/vertiport
elevation
gallois wrote:
If descending to a MDA/MDH you have an add on so as not to descend below the MDA.
I thought that add on was 20ft here but I will have to double check that as the posts here have put a doubt in my mind:)
There is no general 20ft rule – the rule is you must not descent below MDA. Not at all!
Therefore you have to take the decision to stop the descent at some point above the MDA. How far above is depending on many factors: Your ability as pilot, the plane you fly, the weather, your approach speed.
I doubt that there is any pilot in any plane who can fly to less then 20ft above the MDA and still does not get below. That is where the 20ft comes from. If you fly under commercial ops, your op manual might have a higher minimum margin. But also this is only a minimum margin: The rule stays that you must not go below MDA.
My personal m minimum is 50ft above MDA – if and only if I fly my own plane in a “normal” approach in reasonable weather. I know that I need this buffer to make sure I avoid undershooting MDA.
A lot of this depends on what a particular FTO is teaching, which in turn is determined by what the national CAA examiners want to see, and by what pass rate they are trying to achieve (a high 1st time pass rate brings more customers).
Here in the UK, the teaching has been that on an ILS you fly down to the DH exactly, and then decide. Obviously you will dip below it but the DH is designed with that in mind. I discussed this with the CAA IR examiner I had for my initial JAA IR test. He went through the TB20 POH and agreed there is nothing in there about altimeter error etc.
On a nonprecision approach, you are not supposed to dip below the DH (MDH as it is more correctly called). So people are taught to go around at DH+50ft, etc.
Personally, I fly down to the minima on the plate. It is much safer to do that in say OVC002 than to go around at 250ft and fly to the alternate, mess about there, etc. This doesn’t happen often but I have got visual a number of times at the DH.
IIRC, the only scenarios where I have done a missed approach was when it was solid fog, and there was almost no expectation of getting visual anyway. At the end of any long flight, I am not going to try an approach near or at minima when the alternate is much better, because one can’t mess around with fuel.
I’ve been taught at my IR(R) course that if you fly NPA, you add nothing (margin has already been added), but if you fly a precision approach, then you add 50ft to the OCH for altimeter compensation.
Gosh; that’s the other way around from what I got
But anyway the OCH is not the DH. The OCH is just what the CAA plates show. You need a friend with Jepps
Just checked – APM book 5, page 476, step 2: “For precision approach add 50 feet PEC (nil correction for a non-precision approach)”.
:)
