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Thread: Cargo airplane collapsed in Kyrgyzstan

  1. #101
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    Fair, but there are certain areas of that terrain database, namely in direct proximity to airfields, on both sides of the extended centreline where very low altitude flight will naturally occur, where EGPWS (and TAWS) MUST be inhibited.
    The GPWS (and even more the EGPWS) are trend monitors, not static ones. They don't check where you are and how high, but also how much you are descending or climbing and (ofr the E version) where you are heading to. For example, if immediately after take off and while still above the runway you start to descend, the GPS (even without the E) will start to say "don't sink".

    So yes, very low altitude flight will naturally occur in the zone where the plane crashed (or where the alert would be triggered), but not in that combination of vertical speed and heading. The system can easily detect that with the current trend I will end up touching a couple miles past the runway threshold that would be consistent with the heading. Even more, I know that there is a "long landing" alert in some planes, but I don't know if it is part of the EGPWS.

    Anyway, in this case the warnings would have needed to occur over the runway. I highly doubt EGPWS gives altitude alerts because you are too far past the TDZ. That would be cool if it did though.
    I would expect it to do. If you say "too far past the TDZ" then it sounds mild. But we can also say "aiming to a point that is nowhere close to a valid TDZ".

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  2. #102
    Senior Member 3WE's Avatar
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    Quote Originally Posted by Gabriel View Post
    ...Almost every new Cessna C-172 comes out of the factory with Synthetic Vision (SVT) where you can actually see ahead the terrain, runway and obstructions (except inconsistent obstructions like deer or trucks). EVS (enhanced vision system, using an IR camera that can look through the fog and clouds and smoke and depicting the image directly on the PFD, together with the pitch information and sometimes together with the SVT)...
    WOW...

    What happened to the six-pack which lost suction so much that- when practicing IFR skills, it was probably a good idea to try to not use the AI at all and hope that the crazy swinging backup heading indicator would get you to better weather...

    ...and here "we" are calling for similar systems in big shiny jets!
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  3. #103
    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    The GPWS (and even more the EGPWS) are trend monitors, not static ones. They don't check where you are and how high, but also how much you are descending or climbing and (ofr the E version) where you are heading to. For example, if immediately after take off and while still above the runway you start to descend, the GPS (even without the E) will start to say "don't sink".

    So yes, very low altitude flight will naturally occur in the zone where the plane crashed (or where the alert would be triggered), but not in that combination of vertical speed and heading. The system can easily detect that with the current trend I will end up touching a couple miles past the runway threshold that would be consistent with the heading. Even more, I know that there is a "long landing" alert in some planes, but I don't know if it is part of the EGPWS.


    I would expect it to do. If you say "too far past the TDZ" then it sounds mild. But we can also say "aiming to a point that is nowhere close to a valid TDZ".
    Well, apparently it didn't, and it's safe to say that this 2003-build 747 had EGPWS (TAWS) installed. As you say, the principal difference between GPWS and EGPWS if the look-ahead feature, and GPWS is inhibited in landing configuration, so I'm assuming EGPWS is also inhibited in landing configuration UNLESS something in the terrain database presents a look-ahead threat based on the trending path of the aircraft. I'm further assuming that there is nothing threatening in the terrain database between the two opposing glidepaths of the runway. If EGPWS has something like a 'long-landing' feature, I think it would have gone off here and it sure doesn't look like that was the case...

    I'm pretty sure that if you are descending onto any part of the runway in landing configuration, without excessive closure rate, EGPWS isn't going to bother you. Feel free to prove me wrong though.

  4. #104
    Senior Member Evan's Avatar
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    Quote Originally Posted by 3WE View Post
    ...and here "we" are calling for similar systems in big shiny jets!
    Not necessary, due to the flawless airmanship that all airline pilots must certainly possess. Like envelope protections, it would just be another insult.

  5. #105
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    Quote Originally Posted by Evan View Post
    ***Like envelope protections, it would just be another insult.***
    Methinks almost all big shiny jets have stall warnings and stick shakers and pushers and overspeed warnings, and not too many of them had their wings ripped off, nor am I aware of pilots being insulted by said envelope protections.

    I think the complaints are mostly the Airbus-mega-vanilla-computer that makes it behave like a not_airplane, until the computer decides to hell with it, it is an airplane after all...(Acknowledging that one making normal mundane operations can try to ignore that feature and have some fun boring holes in the sky or trees just beyond the show area)...

    ...Still, why no envelope protection for rudders that can be slammed stop to stop by very low input forces and very low input movements?

    As to whether you might actually momentarily need an 80-degreee bank or 60 degree pull up...indeed, that's debatable.

    Now, as to doing something to help with situational awareness...why not. Even with a big accurate HUD of an artificial-but-accurate terrain picture, it's still probably a good idea to nail the ILS and your speeds...lest you come up short like Asiana on a sunny evening or run long like Southwest et al.

    Systems that provide safety checks: Good. Systems that replace pilot skill: Old timers utter the phrase "Puppy Mill"
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  6. #106
    Senior Member 3WE's Avatar
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    Quote Originally Posted by Evan View Post
    Not necessary, due to the near flawless airmanship that almost all airline pilots almost certainly possess....
    Fixed.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  7. #107
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    and GPWS is inhibited in landing configuration
    It is not. This one I know for sure.
    "Sink rate", 'terrain", "woop woop pull up" and even "don't sink" (with a high power setting) all work in landing configuration (not if you are smoothing approaching the middle of the ocean in a landing-like profile, though, so they would not have sounded in this case). "Glide slope" of course is also active in landing config (what would be the point if not), but I don't know what is the criteria that "arms" this mode. This plane crossed the (false) glideslope and obviously deviated from it. [EDIT: Found it: "The mode is armed when a valid signal is being received by the capts glideslope receiver and the radio altitude is 1000 feet or less." I am not sure how this applies in this case, perhaps the GS was not being received anymore when the airplane crossed 1000ft]

    Too low flaps and too low gear are not inhibited but will never be heard in landing config for obvious reasons.

    Feel free to prove me wrong though.
    I can't. I don't have enough knowledge or information. That's why I am using terms like "I would expect that..." or "I would be disappointed if...".

    Well, apparently it didn't, and it's safe to say that this 2003-build 747 had EGPWS (TAWS) installed.
    This is the most convincing part so far. If the plane was equipped with EGPWS, and it was in working order, and it didn't give an alert, then it looks very likely that it would not do it under these circumstances...

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  8. #108
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    Quote Originally Posted by Evan View Post
    BB, Can you tell us what happens on the 744 if the vertical mode goes to GS CAP and then loses the glideslope signal? Does it then transition to V/S by default? This flight transitioned to ALT HOLD when it reached 3400 with no glideslope capture, then flew level until it traversed the mirror glideslope at 9°, which activated GS CAP but of course it flew right through that. Yet it descended on autopilot. Why does it not remain in ALT HOLD in that scenario?
    After talking to my two fellow crew night before last, they both say it goes to V/S. Hope that helps.

  9. #109
    Senior Member Evan's Avatar
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    Quote Originally Posted by BoeingBobby View Post
    After talking to my two fellow crew night before last, they both say it goes to V/S. Hope that helps.
    Yes, thanks. It explains the nice, typical illusion of being on glideslope.

  10. #110
    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    It is not. This one I know for sure.
    "Sink rate", 'terrain", "woop woop pull up" and even "don't sink" (with a high power setting) all work in landing configuration...
    Are you sure about "TERRAIN"? The first terrain warning is "TOO LOW TERRAIN" which my 747-400 FCOM indicates as "Descent below unsafe altitude while too far
    from any airport in the terrain database
    ." And of course it would have to be inhibited within airfields where the aircraft is expected to go below that safe altitude (in landing config) to land.

    This is my assumption of how it works, and it explains why EGPWS didn't save this crew:
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  11. #111
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    Are you sure about "TERRAIN"? The first terrain warning is "TOO LOW TERRAIN" which my 747-400 FCOM indicates as "Descent below unsafe altitude while too far from any airport in the terrain database." And of course it would have to be inhibited within airfields where the aircraft is expected to go below that safe altitude (in landing config) to land.
    I was responding to you and quoted you saying "and GPWS is inhibited in landing configuration".
    Note GPWS without an initial E. The GPWS will not know where the airplane is in relation with the airport.

    So "terrain" would be available, not "too low terrain".
    "Terrain" is a ground closure rate warning (i.e. RA vertical speed), which can be caused by you descending toward the terrain or the terrain raising under you.
    "too low terrain" is a ground closure warning (without "rate") that sounds when you are too close to the ground but not in landing configuration.

    https://www.boeing-727.com/Data/systems/infogpws.html

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  12. #112
    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    I was responding to you and quoted you saying "and GPWS is inhibited in landing configuration".
    Note GPWS without an initial E. The GPWS will not know where the airplane is in relation with the airport.

    So "terrain" would be available, not "too low terrain".
    "Terrain" is a ground closure rate warning (i.e. RA vertical speed), which can be caused by you descending toward the terrain or the terrain raising under you.
    "too low terrain" is a ground closure warning (without "rate") that sounds when you are too close to the ground but not in landing configuration.

    https://www.boeing-727.com/Data/systems/infogpws.html
    Understood Gabriel, but I am talking about THIS accident, and EGPWS, and the pertinent EGPWS warning would be TOO LOW TERRAIN (followed by CAUTION TERRAIN and TERRAIN TERRAIN PULL UP). If those warnings had been active, this accident probably would have been avoided. I'm suggesting (not 100% certain) that the warnings were inhibited because the entire airfield area is an inhibited zone, regardless of the way the airplane is trending (in this case towards a landing near the end of the runway). If I am correct about that, it would seem logical, and not too difficult, to fix that.

    TERRAIN does not apply here because the closure rate was not excessive.

    (With GPWS the TOO LOW TERRAIN warning is ALWAYS inhibited in landing configuration regardless of where the airplane drops below the safe altitude, so I'm not talking about GPWS.)

    FYI: DON'T SINK is also inhibited in landing configuration (gear and/or flaps out) since it is intended for take off or go-around, not landing.

  13. #113
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    If I am correct about that, it would seem logical, and not too difficult, to fix that.
    I agree.

    FYI: DON'T SINK is also inhibited in landing configuration (gear and/or flaps out) since it is intended for take off or go-around, not landing.
    Ok, I was spiting hairs with that. The condition for "don't sink" to be armed is "power above xxx" (i.e. high power) and radio altitude below yyyy. If you are in final approach in landing configuration and start a go-around by advancing the power, and you remain in landing configuration for some seconds, and for whatever reason start to sink, it will sound even if you are in landing configuration.

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  14. #114
    Senior Member 3WE's Avatar
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    How many posts dissecting "if-then" logic, when "watch the needles when doing an ILS in genuine IMC" is the failure here?

    Great to have back-up checks, but instead of redesigning a plethora of XGPWS modes and logic trees, how about the I-pad depicting the view out the window, some boxes to fly through and maybe a flashing red light and a beep for "off course".
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  15. #115
    Senior Member Gabriel's Avatar
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    I am thinking... probably the crossed bars of the Flight Director where nailed in the center of the PFD. Some pilots tend to rely and focus too much in the FD, above other instruments like the ILS or even the attitude indicator.

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  16. #116
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    Quote Originally Posted by Gabriel View Post
    I am thinking... probably the crossed bars of the Flight Director where nailed in the center of the PFD. Some pilots tend to rely and focus too much in the FD, above other instruments like the ILS or even the attitude indicator.

    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Exactly!

  17. #117
    Senior Member 3WE's Avatar
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    Quote Originally Posted by Gabriel View Post
    I am thinking... probably the crossed bars of the Flight Director where nailed in the center of the PFD. Some pilots tend to rely and focus too much in the FD, above other instruments like the ILS or even the attitude indicator.
    Gotcha...

    ...still, the $ to rework all of the XGPWS logic vs. the I-pad app (and you know the I-pad comment is largely sarcasm, but with the genuine statement that we are pretty darn rich when it comes to data and computing power to provide some hellacious synthetic vision for a good ole cross check).
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  18. #118
    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    I am thinking... probably the crossed bars of the Flight Director where nailed in the center of the PFD. Some pilots tend to rely and focus too much in the FD, above other instruments like the ILS or even the attitude indicator.
    And because this is true with some pilots, an avionic line of defense is needed. With EGPWS, I believe we now have a line of defense for every conceivable CFIT scenario except this one. This accident revealed a glaring vulnerability in that line of defense. Closing up that vulnerability should be possible with nothing more than new software. This crash could have just as easily happened to a passenger jet. Hopefully the NTSB will take notice and make a recommendation to modify EGPWS before that happens.

    Essentially we have a perfect storm of:

    - a complacent crew
    - a delayed arrival at the FAF crossing altitude (3,400') preventing glideslope capture
    - a false glideslope signal causing G/S CAP to initiate continued descent to the runway
    - hard IMC, a lack of visual ground reference
    - no automated warning alerting the crew that something isn't right

    Remove any one of those conditions and this crash would not have happened. Guess which of those conditions is easiest to remove...

  19. #119
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    Quote Originally Posted by BoeingBobby View Post
    After talking to my two fellow crew night before last, they both say it goes to V/S. Hope that helps.
    At what point (if at all) would LOC and/or GS bugs start flashing on the PFD?

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