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FAA, NTSB Remain At Odds On ‘Dive And Drive’ Instrument Approaches

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  • #16
    Originally posted by brianw999 View Post
    They say a picture speaks a thousand words so heres a question.....
    That certainly makes sense, although I can think of two exceptions.

    The first is when there's an obstruction somewhere along the ILS path - a hill for example. In that case you'd want to maintain a safe altitude until you're past the hill, descend to a point below the glideslope, and then fly level until you intercept the glideslope. For reasons I don't fully understand, it's better to intercept a glideslope from below rather than from above.

    The second situation, that's really more of a generalization than an "exception", is when you have to call off the approach. Although both can be done, it's probably easier to transition to a missed approach when you're flying straight and level than when you're descending.
    Be alert! America needs more lerts.

    Eric Law

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    • #17
      Originally posted by elaw View Post
      I think one of us must be misunderstanding what "dive and drive" is!
      Adjectives added.
      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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      • #18
        Originally posted by elaw View Post
        That certainly makes sense, although I can think of two exceptions.

        The first is when there's an obstruction somewhere along the ILS path - a hill for example. In that case you'd want to maintain a safe altitude until you're past the hill, descend to a point below the glideslope, and then fly level until you intercept the glideslope. For reasons I don't fully understand, it's better to intercept a glideslope from below rather than from above.

        The second situation, that's really more of a generalization than an "exception", is when you have to call off the approach. Although both can be done, it's probably easier to transition to a missed approach when you're flying straight and level than when you're descending.
        Well, first of all, we are discussing instrument approach here. No one is talking about ILS (and please tell us where an ILS glideslope exists that passes through terrain).

        Now, if you are landing at someplace like Paro, with a serpentine visual approach, then a stable glidesope isn't possible and you must 'dive and drive'. But that's not an instrument approach (it better not be!)

        With ILS, you want to capture the glideslope from below because if you capture it from above you have gone beyond it, you are high and fast, and to get down you must idle the thrust and make a Faustian pact with gravity. This is where a pilot might select an open descent mode like FLCH and end up dropping below the glideslope with no thrust available for a critical number of seconds. Or other bonehead moves made largely because the workload became overwhelming.

        One primary reason we don't like 'dive and drive' is that it creates significant workload at a critical phase of flight, as Brian has pointed out, and has little margin for error. With a CFDA you establish control settings much earlier in the approach, and from that point on must just keep everything stabilized through a series of stabilized criteria 'gates' down to MDA.

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        • #19
          ...while we are cussing and discussing all of this in an attempt to further bolster our already-pretty-darn-but-not-quite-perfectly safe airline travel, don't pretty much all major operators already prohibit the step down when a constant descent option is available via their internal operational rules? Edit: Evan mentioned this above.

          Meaning the government could mind it's own business and keep this as an option for cowboy, stick and rudder operators and the occasional "emergency" situation where an airliner winds up low on fuel?
          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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          • #20
            Originally posted by 3WE View Post
            Broken clouds...

            Admittedly, it's a slightly special situation. Conversely with broken clouds and numerous step downs it could indeed make the difference.
            Yes, it's a slightly 'never-say-never' approach. But why do you need to step down to MDA? Can't you just (being aware in advance of the conditions) calculate a CFDA to put you several miles further out at MDA and then hunt for a window (assuming MSA provides for this)?

            Like so:

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            • #21
              Originally posted by Evan View Post
              Yes, it's a slightly 'never-say-never' approach. But why do you need to step down to MDA? Can't you just (being aware in advance of the conditions) calculate a CFDA to put you several miles further out at MDA and then hunt for a window (assuming MSA provides for this)?
              Well, you've just made this a descend and level-off approach...leaving the lowest and most dangerous level off...95% right back where we started...

              And "assuming the MSA provides" ...that's kind of sort of what the step downs do is address terrain and obstructions along the approach course. I'd again say that it would be pretty rare that the MSA would provide very much to allow a one single step down (whether that step down was a calculated descent or an unspecified-but-still-reasonable descent rate).
              Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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              • #22
                Originally posted by 3WE View Post
                Well, you've just made this a descend and level-off approach...leaving the lowest and most dangerous level off...95% right back where we started...

                And "assuming the MSA provides" ...that's kind of sort of what the step downs do is address terrain and obstructions along the approach course. I'd again say that it would be pretty rare that the MSA would provide very much to allow a one single step down (whether that step down was a calculated descent or an unspecified-but-still-reasonable descent rate).
                You have to make that level-off at MDA anyway and I think it would be safer leveling off from a stablized 3° glidepath than a steeper flight-level change.

                The final leg (the MDA sniff-level) would just be the same as the one on the dive-and-drive so actually MSA isn't an issue. You just arrive there in one glidepath rather than a series of steps.

                Again, I think the problem the NTSB has with drive-and-drive is all the stepping involved, the workload, the risks that come with complexity and the steeper V/S that are involved. Just cut all that stepping out for your 'slightly special situation'.

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                • #23
                  Originally posted by Evan View Post
                  You have to make that level-off at MDA anyway... workload...risks...
                  In response to immediately above: Yes...

                  But recall the beginning- your question (in so many words) was if there were any advantages to step down approaches.

                  I can play what-if games all day long with broken clouds occurring at the perfect place where your even descent is in the clouds and the steeper step down is not (just place little clouds just inside of the corner of Brian's drawing)

                  ...And I can recall some very recent flights when on the ILS (from seat 28A) in ragged-but-not-super-low clouds, I had ground contact and then lost ground contact, so the issue isn't totally without merit.

                  No question that multiple step downs make work.

                  Conversely, one can usually make a counter argument that a 200 ft decision height on an ILS is many times more critical than the more robust safety margins in a step down approach.

                  All this being said, as we both stated above- most major carriers have their own internal bans on the procedure...so maybe they are better off to go missed and land at the alternate, even though a stick and rudder cowboy might properly fly the approach and get in safely and legally.
                  Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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                  • #24
                    Originally posted by Evan View Post
                    Now, if you are landing at someplace like Paro, with a serpentine visual approach, then a stable glidesope isn't possible and you must 'dive and drive'. But that's not an instrument approach (it better not be!)
                    There are a number of serpentine approaches that have you dodging terrain (to be clear: below mountain top levels, dodging mountains)... that are instrument approaches (RNAV / RNP).

                    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                    --- Defend what you say with arguments, not by imposing your credentials ---

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                    • #25
                      Originally posted by Gabriel View Post
                      There are a number of serpentine approaches that have you dodging terrain (to be clear: below mountain top levels, dodging mountains)... that are instrument approaches (RNAV / RNP).
                      Have you ever seen a video of that one? Pure visual by a handful of pilots rated to fly it using landmarks. But yeah, I would hate to be a passenger in IMC on something even remotely like that. Would they ever use a constant descent final approach on such laterally challenging terrain-specific instrument approach?

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                      • #26
                        Originally posted by Evan View Post
                        Have you ever seen a video of that one? Pure visual by a handful of pilots rated to fly it using landmarks. But yeah, I would hate to be a passenger in IMC on something even remotely like that. Would they ever use a constant descent final approach on such laterally challenging terrain-specific instrument approach?
                        Paro? Yes, beautiful visual approach.
                        But there are other winding approaches that are instrument and equally beautiful.

                        Despite saying "Paro, paro..." dozens of times, this approach is NOT Paro



                        I think that the procedure in place back then was the one in page 5 here:


                        But later it was improved to the one in page 1 here due to potential conflict between a plane going around and another one approaching "behind" ("behind" can have a strange meaning in an approach like the previous one).

                        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                        --- Defend what you say with arguments, not by imposing your credentials ---

                        Comment


                        • #27
                          Extremely unstabilized! Incredible airspeed increase on short final!!!!!

                          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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                          • #28
                            Ok, enough is enough with this dodging clouds stuff.

                            The industry has recognised that doing dive and drive to avoid clouds is not the safest way to conduct the approach, and that is the very reason we have continuous descent. It is acknowledged that there are occasions that CDA will mean that you don't land off an approach when you may have been able to do so with a 'dive and drive', but that this benefit does NOT outweigh the risks that you introduce by doing this approach.

                            This has been recognised by all of the major safety organisations and airlines, which is why 'dive and drive' is so rare these days. There is no need to create new ways of doing the approaches... CDA is fine.

                            The only reasons you should be doing a non CDA is for the reasons I outlined before - where CDA is not a practical solution to a very specific approach. And that doesn't include avoiding clouds.

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                            • #29
                              Originally posted by Gabriel View Post
                              Paro? Yes, beautiful visual approach.
                              But there are other winding approaches that are instrument and equally beautiful.

                              Despite saying "Paro, paro..." dozens of times, this approach is NOT Paro



                              I think that the procedure in place back then was the one in page 5 here:


                              But later it was improved to the one in page 1 here due to potential conflict between a plane going around and another one approaching "behind" ("behind" can have a strange meaning in an approach like the previous one).
                              http://www.aip.net.nz/pdf/NZQN_45.1_45.2.pdf
                              F*****g hell ! One thing is for sure, I wouldnt fall out of my seat. My arse would be doing an extreme imitation of a limpet during that approach. Surrounded by, and flying straight towards Cumulo Granitus ....... and then they descend into cloud.
                              If it 'ain't broken........ Don't try to mend it !

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                              • #30
                                Originally posted by Evan View Post
                                Ah yes, point taken MCM. I was thinking that a non-corrupt agency would be a reforming force to a corrupted one, instead of the opposite. What was I thinking...
                                One thing to consider, Evan, may be that just because NTSB does some things that you happen to like, that hardly means they're not also a "corrupt agency". So, at best, this would be a merger of two corrupt agencies, granted, corrupt in different ways, but corrupt nonetheless...

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