Glideslope Intercept Altitude

Discussion in 'Pilot Training' started by HF17, Aug 22, 2022.

  1. Plano Pilot

    Plano Pilot Line Up and Wait

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    DANDY at 1500 gets several pilots using the second method. Can't just use one method.

    00890IL6 (faa.gov)
     
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  2. luvflyin

    luvflyin Touchdown! Greaser!

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    Well you still have the choice whether to dive 200 feet and drive or not:dunno:. Jepp users are probably less likely to boo boo on this one.

    upload_2022-8-22_20-4-30.png
     
  3. dmspilot

    dmspilot Final Approach

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    What is the other choice?
     
  4. asicer

    asicer Final Approach

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    #1 guarantees I'll intercept the GS from underneath. I flew a plane (luckily in VFR) where the GS needle was stuck in the center with no flag. Apparently the wire that deflects the needle upward broke somewhere. Does #2 offer the same indication?
     
  5. luvflyin

    luvflyin Touchdown! Greaser!

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    Stay at 1500 and intercept the GS
     
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  6. dmspilot

    dmspilot Final Approach

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    I thought Plano was referring to people to intercepting at 2,000.
     
  7. luvflyin

    luvflyin Touchdown! Greaser!

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    I know. That they would probably be missing the mandatory altitude at DANDY. I was just saying that if you didn’t, there would still be a dive n drive choice at DANDY. 200 feet worth of dive. Just an academic discussion really. The needle would probably already be moving by then.
     
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  8. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    The glide slope is above 2000 feet at Dandy, FWIW.
     
  9. luvflyin

    luvflyin Touchdown! Greaser!

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    Ok. But ya gotsta be at 1500 at DANDY. At. DANDY is 6 miles out. Do you figure the needle would be moving by then? I forget how wide full needle deflection is on a Glideslope.
     
  10. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    Pretty sure it wouldn’t, but ive never been at 2000 ft there to find out, and I’m not going to look it up. ;)
     
  11. luvflyin

    luvflyin Touchdown! Greaser!

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    I’m talking about being at 1500 like yer supposed to be. Relax, statute of limitations is probably up on that time you was at 2000:fingerwag:
     
  12. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    I learned technique 1. All those misplaced concerns about false glideslopes. I was introduced to #2 when LPV came along (no false glidepath :D). Then I came to the conclusion that worrying about false glideslopes was silly. There are exceptions but procedure design is intended to have the IF or straight in IAF below glideslope/path False glideslopes appear at twice the height of the real glideslope. And early stabilization is less work than dive and drive.

    OTOH, I have a friend who continues to prefer diving down. He claims it works better for him in "best forward speed" situations.
     
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  13. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    Yes. #2 also guarantees you will intercept the glideslope from underneath. (Someone is sure to point out an exception but so what?)

    And I have had the glideslope needle come in and stick too. Mine was in the clouds.
     
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  14. IK04

    IK04 En-Route

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    I poo-poo such responses. :cool:
     
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  15. brcase

    brcase Pattern Altitude

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    Good Discussion...
    Here is the last two sentence for those that want to be well informed...

    "Interception and tracking of the glide slope prior to the published glide slope interception altitude does not necessarily ensure that minimum, maximum, and/or mandatory altitudes published for any preceding fixes will be complied with during the descent. If the pilot chooses to track the glide slope prior to the glide slope interception altitude, they remain responsible for complying with published altitudes for any preceding stepdown fixes encountered during the subsequent  descent."

    Brian
     
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  16. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    As an example, following the glide slope on the LDA 25 at KEGE will put you below at least one of the step downs.
     
  17. luvflyin

    luvflyin Touchdown! Greaser!

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    What’s the feet per mile for 3.8 degrees?
     
  18. dmspilot

    dmspilot Final Approach

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    tan(3.8°) * 6076 ft/nm = 403.6 ft/nm
     
    Last edited: Aug 23, 2022
  19. sarangan

    sarangan Pattern Altitude

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    Why does it have to be one or the other? Why not teach both? Factors like icing, ceiling, etc.. will make a difference. You are teaching them to be flexible and adapt to different situations, not to always do the same thing.
     
  20. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    Excellent response!
     
  21. Witmo

    Witmo Pattern Altitude

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    If you're not established on a published part of the approach, ie. you;re being vectored to the final approach coarse, and you're given permission to intercept, aren't you required to maintain the last altitude given until you're receiving course guidance?
     
  22. dmspilot

    dmspilot Final Approach

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    You are required to maintain the last assigned altitude until given an approach clearance and established on a published approach segment.
     
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  23. IK04

    IK04 En-Route

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    I have taught and demonstrated both methods, depending on the circumstances.

    I have also requested and been approved for a 270 degree intercept on a localizer in a non-radar environment.

    "Own navigation" is a wonderful thing...
     
  24. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    Knowing what you can and can’t do with regard to procedure turns can make a significant difference in the amount of puke you have to clean up. ;)
     
  25. IK04

    IK04 En-Route

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    You mean aerobatics in IMC is frowned upon?

    Wussies!
     
  26. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    I had a guy use up pretty much every bit of protected airspace in a procedure turn trying to fly the standard 45-degree one rather than simply doing a direct entry to a HILPT.
     
  27. luvflyin

    luvflyin Touchdown! Greaser!

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    Can you give us some details on that. I’m having trouble picturing it.
     
  28. IK04

    IK04 En-Route

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    Here's the scenario: An active restricted area North of the airport restricts the flow of traffic inbound to an ILS RWY 1 approach without a long outbound leg and a course reversal several miles South of the FAF. Arriving from the West, I ask for direct to the LOM on and Easterly heading and cross at the assigned altitude.

    Upon station passage, I make a standard rate turn to intercept the localizer and roll out on course, at the GS intercept altitude. There is a lot happening in a short period of time, but after a few successful iterations, it is mostly just a time saver, but the local ATC boys like getting rid of me while I'm out doing multiple practice approaches.

    Oh, I should mention this is in a helicopter, so it may not be quite as fun while trying to slow down and reconfigure an airplane. That would be pretty busy...
     
  29. luvflyin

    luvflyin Touchdown! Greaser!

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    Ok. Sounds like you did a PT. You did it on the side indicated by the Barb and remained within 10 NM. Arriving at a 90 degree angle from the Non Maneuvering side and hanging a 270 on the Maneuvering side is perfectly legal. Some Approaches may have you a little high doing that and intercepting the Glideslope from above though.
     
  30. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    Works well in jets, too.
     
  31. Captain Bubba

    Captain Bubba Pre-Flight

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    Note 2 was added because pilots were getting deviations for intercepting the GS early and not honoring mandatory altitudes on step down fixes. Prior to note 2 being published in the AIM there was an AC on this issue which better explained the problem, but it has to do with separation requirements outside the FAF, particularly in busy areas where mandatory altitudes on step downs are necessary. CDFA and stabilized approaches are a great thing, but a poor excuse for busting an altitude outside the FAF. If you bust DANDY on the TEB ILS RWY 06, you will almost certainly get a number to call.
     
  32. luvflyin

    luvflyin Touchdown! Greaser!

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    Yeah. I sent a change request into the FAA a few years ago about how that Note was sometimes being misinterpreted by pilots and how it might be worded a little better. They acknowledged receipt. Never heard anything else and it hasn’t changed. Do you have that AC number?
     
    Last edited: Aug 24, 2022
  33. Captain Bubba

    Captain Bubba Pre-Flight

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    I’m not even 100% sure it was an AC, but there was published guidance on this issue before they added the note to the AIM. This goes back a few years so I don’t remember the reference. This problem can be very insidious in some situations because on one day you might come down on the GS without problems, but on another the temps are higher, you intercept sooner, start down, and ATC is asking why. In some situations it’s better to let VNAV do your step downs and wait to arm the ILS until right before the FAF. Then you might find yourself above the GS and have to dive for it. It’s certainly not the ideal situation in regards to stabilizing your approach, but it beats having a conversation with FSDO about your future in aviation.
     
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  34. wayneda40

    wayneda40 Pre-takeoff checklist

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    Correct me if I'm off here, but it seems these temperature-related problems can be (and prior to the chart updates, could have been) avoided with systems supporting VNAV (i.e. modern digital autopilots/flight directors):
    • such that all the segments outside the leg leading to the FAF are flown with magenta needles and VNAV advisory glide paths... hitting the stepdown altitudes precisely at each intermediate waypoint...
    • and then auto-switching to green needles once on the segment leading to the FAF and only then capturing the glideslope.
    Also seems to me to be a "best practice" to avoid green needles until the segment leading to the FAF.
    Thoughts?
    Wayne
     
    Last edited: Aug 24, 2022
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  35. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    Pretty much.
     
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  36. wayneda40

    wayneda40 Pre-takeoff checklist

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    @luvflyin , no, the FPL includes all the stepdown waypoints and their corresponding altitudes. The pilot upon being cleared to the first waypoint (and cleared for the approach) simply activates VNAV (and dials ALTS to the FAF altitude)... and the FD/Autopilot then does ALL the stepdowns (there could be a dozen or more stepdowns) without further pilot intervention (but of course, carefully monitoring everything :)). I can confirm this is the case on GFC500/600/700 autopilots (certification of VNAV can vary by airframe, but I've confirmed the above on my DA40 and a Sling TSi).

    The same process also works for VNAV operations on an Arrival procedure.
     
    Last edited: Aug 24, 2022
  37. luvflyin

    luvflyin Touchdown! Greaser!

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    I had deleted that post because I wanted to think some more and hadn’t had a reply yet, but you obviously were as I was doing it. So. How are those Magenta needles generated? It seems that they would be generating a ‘fixed’ Glidepath via GPS, most certainly with WAAS. Just like an ILS generates a ‘fixed’ Glideslope. Therefore subject to the same problems with temperature.
     
  38. MauleSkinner

    MauleSkinner Touchdown! Greaser!

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    The crossing altitudes are indicated altitude, and most of the more advanced systems use baro VNAV until the fix prior to the FAF, even if WAAS-equipped. So you’d cross at the proper altitudes.
     
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  39. wayneda40

    wayneda40 Pre-takeoff checklist

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    The system generates the "vertical" magenta needles (it's actually a chevron VDI on the PFD) by a real-time "drive and drive" calculation of a segment "glidepath" assuring that you reach the next waypoint at exactly the assigned altitude. There's a bit of a description in this video on Modern Avionics -- Vertical Navigation. I would think that this is not subject to temperature and only subject to the appropriate local altimeter setting (as @MauleSkinner notes).
     
  40. luvflyin

    luvflyin Touchdown! Greaser!

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    Ok. If the needles put you over the Fixes at the correct indicated altitude then cool, do it.
     
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