huv wrote:
No, my impression is that Jeppesen plates for 2D approaches show MDH and 3D approaches show DH.
My impression is that Jepp show DA for every 2D approach that can be flown CDFA — which is virtually all of them.
I share that impression (I struggle to find a counter example).
Timothy wrote:
Is that right about the GM?
It’s actually AMC:
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
until we delete it, which we will do in the next few months.
bookworm wrote:
until we delete it, which we will do in the next few months.
No chance of one, nice, neat set of instructions that we can all understand?
No, sorry, silly of me, I’ll go iron my hands.
Timothy wrote:
No chance of one, nice, neat set of instructions that we can all understand?
From a safety point of view there is no problem with using the MDA as the DA. The obstacle margin at the MDA of a non-precision approach is greater than that at the DA of a CAT I approach, so even if you undershoot while transitioning to the climb, obstacles in the final approach area will not be an issue.
There could be a potential problem with obstacles in the missed approach as you would start the climb from slightly below the MDA and not at the MDA as the procedure designer will have assumed. But this would only be an issue if are still below the MDA at the MAPt and that will only happen if the MAPt is very close to the point where you initiate the go-around. Typically the MAPt will be at the threshold which (assuming a 5,2% nominal glidepath, an approach category A aircraft and the lowest possible MDH) will be at least 25 seconds or 0.8 NM away — usually considerably more.
Even with the CDFA technique you have to respect the MAPt (in case your actual glidepath is too shallow) so if you are bothered by the risk of missed approach obstacles, just “move” the MAPt slightly earlier.
I would rather take 15 seconds (say) away in case of timing the MAPt or 0.5 NM (say) in the case of DME distance and use the exact MDA as DA for a CDFA.
I consider the risks of using the MDA as a DA far less than the risks of doing a go-around, missed approach and diversion.
Timothy wrote:
No chance of one, nice, neat set of instructions that we can all understand?
Well that’s the plan. We’ll see what emerges.
Airborne_Again wrote:
My impression is that Jepp show DA for every 2D approach that can be flown CDFA — which is virtually all of them.
The US Jepp charts show MDA(H) for 2D approaches.Both the MDA and the MDH are charted, the latter in parens. If the procedure is approved for CDFA and using a DA in lieu of the MDA, then the note “Only authorized operators may use VNAV DA in lieu of MDA(H)”. The runway and obstacles have to be compliant with the guidance in C073 and the operator must be approved. Not all runways have this option and all those that are not covered under part 139 are excluded. Jeppesen released a Briefing Bulletin that discusses this topic in detail.
How does whether an operator is “authorized”/“approved” change the obstacle situation?
It doesn’t change the obstacle situation, but since this authorization is withheld unless the approach and runway meet specific requirements that are evaluated for each approach before the note is added, it indicates that it is safe to use the DA in Lieu of an MDA for the evaluated procedure. At one point, Jeppesen was adding the note on any approach that had a published VDA, but there were cases of aircraft hitting trees. I know of one approach that still has a published VDA, but if you follow it, you will need to pass thru a ridge at 100 feet below the summit. This approach does not meet the new criteria that Jeppesen needs to meet in order for the note to be added.
