TDJ737 wrote:
1) You need at least gps to identify the point where to start the continuous descend.
Not quite, it’s not “at least GPS”, it’s whatever distance method is used in the procedure, more specifically, what is quoted on the altitude/distance table.
So if the distance quoted in the distance vs. altitude table is a DME, then you need a DME. Such is the case of the NDB approaches at East Midlands and Cranfield that I posted above.
If it’s a GNSS distance, as is the case of the very first plate on this thread and also the Tenerife South NDB 07 approach, then you need GNSS distance.
TDJ737 wrote:
2) You can continue to the MAP at MDA as far as I understand.
Depends on the technique you are using.
If you are flying using the CDFA technique, once you hit your DDA (derived decision alttitude), you go around.
If you are flying using non-CDFA (dive and drive), you descend to your MDA (plus a sensible allowance), you level off, and you “drive” to the MAP. Then go around at the MAP.
Now to confuse things even further, Cranfield’s NDB DME Rwy 21 has a procedure for the case where one doesn’t have a DME. It even has different CDFA minima for the cases “with DME” and “without DME”.
In the no-DME case, one descends to a platform altitude of 1560’ before hitting the CIT beacon (the FAF) and then commences a descent doing one’s best to maintain a 3º glidepath based on GS and V/S (with the table as reference on the plate conveniently). Once you hit the DDA (based of the “w/o DME” figure on the middle column), you go around.
The key here is that the procedure is increasing the minima for the w/o DME CDFA case.
It hints at the fact that the CDFA approach would have to be flown with a DME in any case if the plate didn’t offer w/o DME minima.
The alternative would be for a non-CDFA minima to be published, but in this case it would have to be flown using the “dive and drive” technique, not the CDFA technique.
Alpha_Floor wrote:
If you are flying using the CDFA technique, once you hit your DDA (derived decision alttitude), you go around.
That was my understanding there is no point flying CDFA if you are leveling off to go to MAPT at DDA, you lose the most important thing when flying an approach, stability !
You may walk away from a stable approach without being able to see the runway at MDH 
You will not walk away from an unstable approach where you see the runway at MDH
Otherwise everybody will go for an overhead joins and spiral dives !
gallois wrote:
Dive and Drive is based on an MDA in Europe as well, but many NPAs also have a CDFA now.
US government charts do not have CDFA charted on NPA procedures, but there is a VDA and TCH charted on most RNAV straight in procedures. The VDA is a visual decent angle and is what a pilot would use if they flew the procedure using the CDFA technique. If there are obstacles in the visual segment that would interfere with a stabilized approach to the runway using the VDA, the VDA is not charted and a note that says “Visual Segment – Obstacles”. In either case, as long as the VDA is coded in the database, +V is offered by the WAAS GPS navigator. If you follow the +V advisory glidepath below the MDA, you are at high risk of removing yourself from the gene pool. Using the CDFA technique in almost all cases requires greater visibility than the dive and drive technique. For Turbojet, CDFA is the recommended technique because of the higher momentum and slower spool up time, but for many piston aircraft, flying steeper angles than 3 degrees is safely and easily piloted. Power off in my Bonanza is close to 8 degrees, so 6 degrees is easy to manage will still keeping some power on.
Ibra wrote:
That was my understanding there is no point flying CDFA if you are leveling off to go to MAPT at DDA, you lose the most important thing when flying an approach, stability !
If you do that, you’re not even flying CDFA. It’s part of the technique that you go around at the DA.
Alpha_Floor wrote:
Now to confuse things even further, Cranfield’s NDB DME Rwy 21 has a procedure for the case where one doesn’t have a DME. It even has different CDFA minima for the cases “with DME” and “without DME”.
[…]
The key here is that the procedure is increasing the minima for the w/o DME CDFA case.
It hints at the fact that the CDFA approach would have to be flown with a DME in any case if the plate didn’t offer w/o DME minima.
I disagree. All NPAs are constructed with Dive-and-Drive in mind, not CDFA. The reason for the higher minimums without DME is that the MAPt would be less precisely determined (by timing) so the MDA is affected by obstacles in a larger area. This is unlikely to affect a properly flown CDFA as you will start a go-around well before the MAPt.
E.g. assuming a groundspeed of 100 knots, you will hit the MAPt after 2 minutes 10 seconds, while on a properly done CDFA, you will hit the (DME) DA after 1 minute 38 seconds. So on a CDFA you have to be off by ≈30% in your GS and/or ROD to go around after the nominal MAPt. This is not very likely.
