Video and Discussion - Burley, ID accident. Was "Gryder"

Discussion in 'Aviation Mishaps' started by LesGawlik, May 14, 2022.

  1. Turbo-Arrow-Driver

    Turbo-Arrow-Driver Pre-takeoff checklist

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    You've got it backwards. The dot is exactly like the CDI needle on an ILS approach. The middle line is you and when the needle goes low, you increase descent rate to catch it.

    No, I don't believe the G1000 will do that. It will track the shallower descent angle from HIKLO to JAMID, and then switch to the faster descent after JAMID. There won't be any "ooops" from the G1000, suddenly showing you way off altitude.
     
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  2. wayneda40

    wayneda40 Pre-takeoff checklist

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    As @Turbo-Arrow-Driver requested, here's a no-spiff video of the G1000 and GFC700 autopilot flying the RNAV 20 at KBYI on the sim (X-Plane 11). Although I've not flown the approach IRL, my real-life experience (>2000 hours) in a DA40 with G1000/GFC700 would agree quite well with this simulator performance.

    Bottom line: the magenta diamond -- i.e. the GP symbol on the Vertical Deviation Indicator (VDI) -- would not abruptly move upon reaching JAMID, although indeed the pitch might adjust to follow the next segment of the approach.

     
    Last edited: May 18, 2022
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  3. Turbo-Arrow-Driver

    Turbo-Arrow-Driver Pre-takeoff checklist

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    So, can you run that again, and stop the simulator at about 1/2 NM before RW20? Just set the airspeed to zero...can you do that with xplane? Once it's stopped then bump the a/c altitude up by 80 or 100 feet and see what happens to the vertical deviation diamond? I was able to do that with the Garmin simulator but don't know if xplane can do that.
     
  4. wayneda40

    wayneda40 Pre-takeoff checklist

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    I'll have to think about how to do that in X-Plane. No doubt the magenta diamond would be below the aircraft, by how many "dots" high we would be I'm not sure. I'll see if I can duplicate.
    Wayne
     
    Last edited: May 18, 2022
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  5. exncsurfer

    exncsurfer Pattern Altitude

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    Does this math look right, for comparing a 3.2 degree glide slope with a 3.75 degree slope:

    if 90 knots is 9114 feet per minute

    3.2 degree glide based on tan(3.2)*9114 = 509 feet per minute descent rate @ 90 knots

    3.75 degree glide based on tan(3.75)*9114 = 597 feet per minute descent rate @ 90 knots

    would put you 88 feet high after a minute on original slope.

    divergence of 1.5 (rounded) feet per second if you maintain original slope.

    I don't know how fast that will make the slope indicator fall away.
     
  6. luvflyin

    luvflyin Touchdown! Greaser!

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    Ok. I think Garmin will let you use either the Jepp data base or theirs, the Garmin base. Look at the Jepp Chart I posted in # 34 above. Do you think that’s going to make a difference? Like if you have the Jepp data base, it will give you a constant 3.75 angle starting 4.5 miles out but if you have the Garmin data base it will give you the angle from HIKLO to JAMID and the change to 3.75 at JAMID.
     
  7. luvflyin

    luvflyin Touchdown! Greaser!

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    Which data base do you use? Jepp or Garmin.
     
  8. wayneda40

    wayneda40 Pre-takeoff checklist

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    That's a good question. X-Plane uses the navigation database from Navigraph, which supplies monthly database updates to simulators of all sorts.

    "Our Navdata product is sourced from Jeppesen, a professional navdata provider for major airlines worldwide.", Navigraph​

    My uncalibrated understanding of the IRL G1000 is that the "navdata" (i.e. that which goes into the FMS, i.e. FPL of the GPS) is all from the same source, most likely Jeppesen. The "charts" data (i.e. approach plates) in a Garmin MFD can come from either Garmin or (for extra $$$) from Jepp.
     
    Last edited: May 18, 2022
  9. Turbo-Arrow-Driver

    Turbo-Arrow-Driver Pre-takeoff checklist

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    I agree that your math is correct.
     
  10. Turbo-Arrow-Driver

    Turbo-Arrow-Driver Pre-takeoff checklist

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    Yes, that's the other way the FAA says you can fly this approach. Instead of having a change of descent angle at JAMID, delay the start of descent (about 1/2 NM in this case) so that the entire descent is at the VDA of 3.75 degrees. You still cross JAMID at the proper altitude, but a change in descent angle is not required.

    So I tried both Jepp and Garmin data bases in the simulator with the same result. But...when I watched the simulator closely, it was doing the Jepp thing -- delayed start of descent. wayneda50's simulator appears to do the other thing -- start descent at HIKLO and then use steeper angle at JAMID.

    I guess the question of how the G1000 in N928JP behaved is not clear maybe. Did it also depend on what firmware version was installed? OTOH, the actual change in required descent rate isn't all that much (e.g. 522 to 597 fpm at 90 kt) so I'm not sure how important that would be.

    The main question I was trying to answer was how quickly the VDI would head south at JAMID if the a/c did not increase descent rate. The answer to that seems to be not very fast, so Gryden's assertion that the change in angle was a "curve ball" thrown to the pilot doesn't hold water in my book.

    The other question is, how many dots off would the VDI be at impact with the tower? If the G1000 scaling is the same as the simulators I tried it would have indicated the a/c was about 1-1/3 dots low. That's mostly just curiosity on my part.

    And I suppose it's good to keep in mind (w/o speculating about what actually happened) that below MDA, the pilot is required to be in visual contact with runway environment, not on the guages...and so Garmin would not be expecting a pilot to follow the slope all the way to landing.
     
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  11. luvflyin

    luvflyin Touchdown! Greaser!

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    If it’s true that some Garmins do in fact give you a ‘two stage’ angle on the VDI that would be just a wrong thing to ever have done in my opinion. The thinking would have to have gone something like this. Ok, there’s this altitude at HIKLO and the altitude at JAMID. We want to give the pilot something to follow so he doesn’t maybe get a bit steep and have to level off before getting to JAMID so we’re going to give him the angle from HIKLO at 6000 to JAMID at 4800. Then, when he gets to JAMID we’re going to change it to this 3.75 degree VDA angle thing. 1.6 miles from the Runway on an Approach with a 1 mile Visibility Minimum. It’s been changed to 1 1/8 now btw and was always 1 1/4 for Cat C.
    @midlifeflyer , you are a GPS Navigator guru. Have you been following this? Do you know of any time Garmin, or any box maker, did this change the angle thing?
     
    Last edited: May 19, 2022
  12. Turbo-Arrow-Driver

    Turbo-Arrow-Driver Pre-takeoff checklist

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    Well, I think this gets into a very subjective topic. I won't argue with your viewpoint, but here's mine.

    With a 90 kt ground speed on this approach the descent rate to trace a straight line from HIKLO to JAMID is 522 fpm. That increases to 597 fpm after JAMID. See the image of a typical VSI gauge below for context. I've photoshopped in copies of the needle at about 520 fpm and 600fpm.

    I've flown enough instrument approaches (both practice, and in IMC) to know that when you throw in the effects of turbulence and varying wind speed and direction during the approach, going from 522 to 597 is not all that much of a change. Although your goal is to achieve an average descent rate that's correct, the gauge may be fluctuating +-100 fpm or more the whole time.

    In summary, my take on this is that the change in angle is not large enough to present a serious challenge for a proficient pilot. I also agree that a constant rate would still be preferable.

    But again, this is a very subjective topic and others will have different opinions, and that's okay with me too. It's not like I've never been wrong before ;).

    VSI-Demo.jpg
     
  13. luvflyin

    luvflyin Touchdown! Greaser!

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    Yeah, it’s not a big angle change. And we don’t really know for sure Garmin does it. But there are some clues they do/did. If so, it just doesn’t make sense to me. It nullifies the whole concept of why VDA was invented in the first place. Constant Angle of Descent down to the runway. Why change the angle. Even though it doesn’t “…present a serious challenge for a proficient pilot…” why test that proficiency? Is there anything to be gained by the vertical dogleg thing at the Step Down Fix? Anything? I can’t see it.
     
  14. wayneda40

    wayneda40 Pre-takeoff checklist

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    I agree that the angle change is small. Just a clarification on terminology (and Gryder made this error also)... the FAA does not term this "constant angle of descent" but rather "Continuous Descent Final Approach" (FAA AC 120-108). One could argue that continuous descent does not necessarily mean constant angle.
     
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  15. Turbo-Arrow-Driver

    Turbo-Arrow-Driver Pre-takeoff checklist

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    I think you raise a couple of questions which could perhaps be explained by someone who knows a lot about TERPS and the design of these approaches.

    BTW, it's worth reading the first few pages of AC120-108 if you haven't. There's not too much bureaucratic non-sense to wade through.

    Anyway, I am curious about the answers to these:
    1. Why the step-down fix? What about this approach requires that?
    2. Why not move HIKLO a bit (0.5NM or so) closer to RW20 so the descent angles don't change?
     
  16. luvflyin

    luvflyin Touchdown! Greaser!

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    Ok. The correct term is Continuous Descent Final Approach. I’m all ears to listen to the argument about how that somehow results in other than a constant angle.
     
  17. wayneda40

    wayneda40 Pre-takeoff checklist

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    @luvflyin ... I think the "continuous descent" term is being used by the FAA to differentiate that strategy from the traditional "dive and drive" (i.e. descend, hold altitude, descend, hold altitude, etc). We could have different descent angles for each segment of a multi-stepdown approach, yet never actually level out and hold altitude... and that would still be a "continuous descent".
     
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  18. luvflyin

    luvflyin Touchdown! Greaser!

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    Just read it. The key point reference what we’ve been discussing here about how Garmin may display it on the VDI is:

    (1) Examples for Calculating Descent Point for Stepdown Fix Associated VDA. Two examples of how pilots may fly the approach are:
    • Descend from the FAF at the shallower rate in order to cross above the stepdown fix altitude and then transition to published VDA, or
    • Begin a descent at a point past the FAF that will allow the aircraft to descend at the published VDA and still clear the stepdown fix altitude.

    I’ll stand by my arguments above in post #’s 131 and 133 that there is no advantage to the first example and compelling reasons to use the second example.
     
  19. luvflyin

    luvflyin Touchdown! Greaser!

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    1. Nothing requires the step-down fix. They could have made the MDA 4800 and just let it go at that. But there was a way to get a lower MDA by establishing the Fix with a Minimum Altitude and get a lower MDA.

    2. Maybe they will. There is an Amendment of this Approach scheduled for publication 9/8/2022
     
  20. Palmpilot

    Palmpilot Touchdown! Greaser! PoA Supporter

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    I can confirm that. I am responsible for keeping the database up-to-date in the G1000 plane based at my CAP squadron, and we recently switched from Jeppesen to Garmin for our database subscriptions. (I don't know why.)
     
  21. luvflyin

    luvflyin Touchdown! Greaser!

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    I was just asking is are Continuous Descent and Constant Angle somehow different. We already know what ever you name it, it’s the alternative to dive n drive.
     
  22. dmspilot

    dmspilot Final Approach

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    CDFA does not require a constant angle. That distinguishes it from CANPA (constant angle nonprecision approach). Every CANPA is a CDFA, but a CDFA does not have to be CANPA.
     
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  23. luvflyin

    luvflyin Touchdown! Greaser!

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    Ok. Got it. If you start descending and you don’t stop and level off you are CDFA. And yeah, you can change your rate and angle during the descent and still be ‘continuously’ descending. Let’s throw Stabilized Approach into it. Stabilized Approach is the thing this whole CDFACANPAVDA thing is trying to achieve. Don’t you big iron guys have some kind of rule that if you don’t have it dialed in long before 1.6 miles from the runway, it’s go around time?

    4. BACKGROUND. Controlled flight into terrain (CFIT) is a primary cause of worldwide commercial aviation fatal accidents. Unstabilized approaches are a key contributor to CFIT events. Present NPAs are designed with and without stepdown fixes in the final approach segment. Stepdowns flown without a constant descent will require multiple thrust, pitch, and altitude adjustments inside the final approach fix (FAF). These adjustments increase pilot workload and potential errors during a critical phase of flight. NPAs designed without stepdown fixes in the final segment allow pilots to immediately descend to the MDA after crossing the FAF. In both cases, the aircraft remains at the MDA until descending for the runway or reaching the missed approach point (MAP). This practice, commonly referred to as “dive and drive,” can result in extended level flight as low as 250 feet above the ground in instrument meteorological conditions (IMC) and shallow or steep final approaches. Figure 1A, Approach Example Without Using Continuous Descent Final Approach, Appendix 1, illustrates the disadvantages of the “dive and drive” technique.
    a. Stabilized Approaches. A stabilized approach is a key feature to a safe approach and landing. Operators are encouraged by the FAA and the International Civil Aviation Organization (ICAO) to use the stabilized approach concept to help eliminate CFIT. The stabilized approach concept is characterized by maintaining a stable approach speed, descent rate, vertical flightpath, and configuration to the landing touchdown point. Depart the FAF configured for landing and on the proper approach speed, power setting, and flightpath before descending below the minimum stabilized approach height; e.g., 1,000 feet above the airport elevation and at a rate of descent no greater than 1,000 feet per minute (fpm), unless specifically briefed. (Refer to AC120-71.)
     
  24. dmspilot

    dmspilot Final Approach

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    Depends on what you mean by "dialed in." There's no requirement to maintain a constant descent rate; that would be impossible anyway. Even if the angle is constant the descent rate will vary with wind, vertical crosstrack error, etc. The descent rate must simply be 1,000 fpm or less. The stabilized approach criteria must be met by 1,000 feet AFE, so about 3 miles.
     
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  25. Turbo-Arrow-Driver

    Turbo-Arrow-Driver Pre-takeoff checklist

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    Hmmm, so (1) how do you know that (no step down reqd)? I'm not questioning your answer, but I'd like to know more...I assume they don't just thrown in a step down fix just for grins.

    And (2) how do you know that? Where do you look to see scheduled revisions? And is there a sneak preview available or a hint about what changed?
     
  26. luvflyin

    luvflyin Touchdown! Greaser!

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    Yeah, rate will change on a constant angle as speed changes. Let’s take rate of the discussion other than it better not be more than a thousand. I’m talking about the pros and cons of these examples

    (1) Examples for Calculating Descent Point for Stepdown Fix Associated VDA. Two examples of how pilots may fly the approach are:
    • Descend from the FAF at the shallower rate in order to cross above the stepdown fix altitude and then transition to published VDA, or
    • Begin a descent at a point past the FAF that will allow the aircraft to descend at the published VDA and still clear the stepdown fix altitude.

    Can you see any reason to use the first example? Don’t know how long you’ve been following along here. What we’ve been talking about is how GPS Navigators display it on their VDI. It seems that maybe Garmin sometimes uses the first example giving a ‘bent’ glidepath so to speak.
     
  27. dmspilot

    dmspilot Final Approach

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    Yeah, the FMS in my aircraft computes an advisory vertical path from the FAF to the runway. It doesn't take into account stepdown fixes. If there is one, it is up to you to do the shallow/steep thing. Common cause of busted checkrides and PCs in the sim, at least that's what I've heard.
     
  28. luvflyin

    luvflyin Touchdown! Greaser!

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    I just said it would only be required to get an MDA lower than 4800. So they did throw it in. Not for grins but to get a lower MDA.
    https://www.faa.gov/air_traffic/fli...ab=productionPlan&nasrId=BYI#searchResultsTop

    Start here to find out how to use the IFP Gateway
    https://www.faa.gov/air_traffic/flight_info/aeronav/procedures/
     
  29. Turbo-Arrow-Driver

    Turbo-Arrow-Driver Pre-takeoff checklist

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    Thanks for the IFP Gateway link...that's cool.

    Regarding the stepdown fix, I'm confused. Why is it necessary to get an MDA lower than 4800? I'm fairly ignorant when it comes to TERPS and the design of procedures. I do have a copy of TERPS but wouldn't know where to look for something like that.
     
  30. luvflyin

    luvflyin Touchdown! Greaser!

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    I’m not saying it’s necessary to get a lower MDA. I just said that the step-down is necessary to get a lower one. There is an obstacle there that requires descent to not go below 4800 until passing it. If a Fix can be put there to identify when past it then cool, put the Fix there and now you can go lower.

    There are some Approaches with 2 MDA’s. The lower one will say something like ‘with ABCDE’. ABCDE might be a DME Fix or an Intersection. If a DME Fix, and DME isn’t required anywhere else on the Approach, there will be that Note on the line of Minimums. If an Intersection there will be a Note that says ‘dual VOR receivers required for ABCDE.
     
  31. Tarheelpilot

    Tarheelpilot Final Approach PoA Supporter

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    Yes. That has been discussed here in the past. The guy has always been a narcissistic prick from what I hear. He’s just taken the act online to feed his ego. But shoot that’s like 95% of the yOutUbers. Just don’t watch his videos. Problem solved.
     
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  32. Turbo-Arrow-Driver

    Turbo-Arrow-Driver Pre-takeoff checklist

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    Actually, I meant -- why do you need the stepdown fix if you want a lower MDA -- but you answered it anyway, so thanks. It's most likely the stacks at the plant -- and that also explains why the first segment of the final approach is at a more shallow angle -- to clear the obstacles.

    So next question -- why not just move the FAF (HIKLO) a bit closer to RW20 so that the entire approach is at the 3.75 degree slope? Something like 1/2 NM closer would do the trick. Does that make the final segment too short or something?
     
  33. Palmpilot

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  34. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    1. Fly down to MDA as depicted.
    2. If you don't have good visuals at the MAP, don't descend; fly away.

    /handwringing about unimportant details.
     
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  35. Salty

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    I kinda feel like maybe a lot of folks are thinking “holy crap! I’ve done stuff like she did before, somebody should do something!” When the only “something” that is needed, is what you just said.
     
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  36. luvflyin

    luvflyin Touchdown! Greaser!

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    I think that might be a good idea. Put it 4.5 miles out there where Jeppesen depicts the start of a VDA. But it wouldn’t surprise me if there was a TERP’s rule that precluded putting it that close. Unless Approach says cross HIKLO ‘at’ 6000, or you were already at 6000 when you got the Clearance, you can just cross it higher and give yourself a longer run on a 3.75 degree ride down the chute.

    upload_2022-5-20_8-43-47.png
     
  37. luvflyin

    luvflyin Touchdown! Greaser!

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    Yup. That be the golden rule. Are you seeing something here that anybody thinks differently?
     
  38. Hector Parra

    Hector Parra Pre-takeoff checklist

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    I'm learning a lot from this thread, thank you all
     
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  39. TrueCourse

    TrueCourse Line Up and Wait

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    There are FMS systems that automatically create the correct path to honor step down fixes, I just haven’t figured out all the Garmin logic yet. I did notice the GTN trainer at this airport will show you the path (VNAV page, path in degrees) being used as you get close the FAF, then crossing the FAF the path isn’t displayed (VNAV page). Has something to do with the step down or non precision nature of the approach.
     
  40. luvflyin

    luvflyin Touchdown! Greaser!

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    Do the FMS's give you the same angle from the FAF to the step-down as the VDA after it?