Originally Posted by swh
(Post 11213812)
They are step down fixes, you cannot fly below those altitudes at those distances, if you do go around. If you want to know why have a look for “VABB Aerodrome Obstacle Chart Type-A RWY 32” on the inter web. Some thought needs to be made on how you are going to fly the approach now that you know what the chart is saying. They are charted this way because blindly using VNAV/LNAV may not guarantee obstacle clearance. If you blindly fly a 3.3 degree FPA or a VNAV path that would be rounded to 3.3 degrees you could fly below the step down fixes which compromises the designed obstacle clearance.
|
Originally Posted by FullWings
(Post 11214019)
That applies generically to every instrument approach: don’t fly below hard altitudes at fixes. If it is coded correctly in the database, then the automation (monitored) should respect these altitudes; if you’re using basic modes you make sure you cross these fixes at or above. Why should this particular NPA be “special” and what’s the proposed difference in technique between flying this and a VOR/DME anywhere else?
|
Originally Posted by Vilas
Flying the approach conventionally without the FMS, at DME fixes you sometimes land up high or low and then correct the descent for the next DME. In this procedure the DME fixes are hard safety altitudes you cannot go below. So you will have treat them as minimums and that cannot be progressively done all the way to the lowest minimum of 2.8DME. so if the fixes are not coded in the FMS then the highest minimum will apply whether you use the FMS or fly with manual vertical guidance.
In any case, that is what the dist/altitude table is for. Follow that, either using FMS VNAV if approved, or manually, and you will miss all the steps. Which brings us back to the original question. Why are there 3 MDAs and when would you use each one? |
Originally Posted by Capn Bloggs
(Post 11214076)
Only if that is what your SOP says. Surely you are not suggesting you step down fix in the altitude selector and treat each as an MDA until you are past it?
Approximately 2 NM before the final approach fix, set the first intermediate altitude constraint or MDA(H). Set the MCP altitude to the nearest 100 foot increment at or below each intermediate altitude constraint. When the current constraint is assured, set the next constraint before ALT is engaged to achieve a continuous descent path. |
Originally Posted by vilas
(Post 11214034)
Flying the approach conventionally without the FMS, at DME fixes you sometimes land up high or low and then correct the descent for the next DME. In this procedure the DME fixes are hard safety altitudes you cannot go below. So you will have treat them as minimums and that cannot be progressively done all the way to the lowest minimum of 2.8DME. so if the fixes are not coded in the FMS then the highest minimum will apply whether you use the FMS or fly with manual vertical guidance.
The procedure under discussion is not available without DME, so the fixes will always be there to check. If you don’t have an FMS but do have a VOR receiver with DME, you should be able to use the lowest minima for your aircraft category? An FMS 3D approach has different tolerances. |
Set the MCP altitude to the nearest 100 foot increment at or below each intermediate altitude constraint. When the current constraint is assured, set the next constraint before ALT is engaged to achieve a continuous descent path. |
Originally Posted by Capn Bloggs
(Post 11214076)
Only if that is what your SOP says. Surely you are not suggesting you step down fix in the altitude selector and treat each as an MDA until you are past it?
In any case, that is what the dist/altitude table is for. Follow that, either using FMS VNAV if approved, or manually, and you will miss all the steps. Which brings us back to the original question. Why are there 3 MDAs and when would you use each one? |
Interesting. I think that it is actually the opposite way round: using raw data and VS/FPA, you can ensure that you are at or above any hard heights by adjusting the vertical profile; if you’re using VNAV (3D) then up to 75’ deviation is allowable and there is no way of controlling that short of using another mode and/or taking the autopilot out, which is contrary to many carriers' SOPs for this type of approach.
All this could be made moot by coding a straight-in RNP procedure like they’ve done with all the other runways. It would even avoid flying directly over the obstacle! |
Originally Posted by FullWings
(Post 11214016)
We have authorisation in our FOMM to treat MDA as a DA with no increment on a CDFA; I don’t think we’re the only ones...
However on PPRuNe not allowed to discuss lest the wrath of the Oztronauts is unleashed, mate. Especially those who think altitude table distance table should be mirrored on alt selector. |
Please can you explain the geometry Flight Detent, I'm genuinely trying to get my head around that one.
Thanks TeeS |
Originally Posted by Flight Detent
Especially those who think altitude table distance table should be mirrored on alt selector.
Vilas, if you're worried about clipping a step, fly the profile + 100ft. Better than resetting the altitude selector three times inside the FAF. |
Originally Posted by Capn Bloggs
(Post 11214561)
That's not me. I say set the real MDA (650) and fly down the profile. Been doing it for years.
Vilas, if you're worried about clipping a step, fly the profile + 100ft. Better than resetting the altitude selector three times inside the FAF. |
I'd say use one minima, either 2.8 or 3.8 if vis is more then 3k, if vis is below 3k you need D2.8... Only thing i can think of why use the 3.8 is some better than standard missed approach climb gradients needed below 780', but that is usually depicted on the chart when that's the case...
|
The way I would fly this:
- set the lowest MDA if using FMS vertical guidance, with SDF1 and SDF2 correctly coded. - monitor - set the lowest MDA if using raw data, ensuring to be at or above the SDFs while monitoring and correcting the profile all the way down. In case of a Missed approach - Do not descend below the MDA that is relevant for the segment at the commencement of missed approach. (Eg if the missed approach is commenced between D7.5 and D3.8 - the 1330’ MDA would be applicable) |
Originally Posted by TeeS
(Post 11213959)
Hi KingAir
That was one of my early thoughts about it but I think there are three problems with looking at it that way: 1. It produces one of the most complex approach briefs ever. 2. Can you continue the approach that requires DME once the DME fails, Note 1 in bold? 3. If you do continue, where is your missed approach point? Cheers TeeS 2. Once you have commenced the final approach, I guess you could. That was the whole point of my previous post, because obstacle clearance is guaranteed. 3. When flying a CDFA you go around once reaching you minima and no contact. The missed approach an be flown without DME. KA. |
KingAir1978
Note 1: DME Required. In plain English, if the DME fails (and you have not yet achieved the required visual reference) you cannot continue the approach. It is NOT optional. I do hope you are not a professional pilot. |
Originally Posted by Clop_Clop
(Post 11214599)
I'd say use one minima, either 2.8 or 3.8 if vis is more then 3k, if vis is below 3k you need D2.8... Only thing i can think of why use the 3.8 is some better than standard missed approach climb gradients needed below 780', but that is usually depicted on the chart when that's the case...
The two step down fixes in this case are required because of the obstacles on final, the only other reason for step down fixes is when the final segment is very long an extra vertical splay needs to be applied, using a step down fix in those cases resets the final segment distance. |
On some VOR DME Charts three different MDAs are mentioned for different DME distances, Can someone please explain. Please see the attachment. The issue was about MDAs for this approach and why they have three ones available. Of course need to assume the appch is flown per chart vor cdfa and with dme and also comply with the at or aboves for any fixes there as well... My point was about the 650' (w D2.8) or 780' (w D3.8) minimas earlier. |
Originally Posted by KingAir1978
(Post 11215079)
1. Yes...
2. Once you have commenced the final approach, I guess you could. That was the whole point of my previous post, because obstacle clearance is guaranteed. 3. When flying a CDFA you go around once reaching you minima and no contact. The missed approach an be flown without DME. KA. |
Originally Posted by vilas
(Post 11216396)
You require DME and ht/dist check also. Air Canada SOP didn't have it they crashed short of RW dispite being on CDFA profile only a parallel little short of the actual.
That a/c https://www.tsb.gc.ca/eng/rapports-r.../a15h0002.html busted minima by 380 feet without visual reference. If they followed the charted profile (some pilots do with their IR not SOP) they may had just crashed onto the runway instead of ploughing through the ravine. Like these clowns https://aviation-safety.net/database...?id=20150304-0 |
All times are GMT. The time now is 09:59. |
Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.