Below glidelope?

Discussion in 'Cleared for the Approach' started by AndrewX, Jan 2, 2018.

  1. AndrewX

    AndrewX Pre-Flight

    Joined:
    Nov 14, 2017
    Messages:
    63
    Display Name:

    Display name:
    Andrew
    If I'm on a precision approach and I find myself below the glideslope, say by one tick mark, should I climb to intercept or hold altitude until I intercept? For the sake of this question, let's assume I'm right on the localizer.
     
  2. jordane93

    jordane93 Final Approach

    Joined:
    Sep 9, 2013
    Messages:
    8,374
    Location:
    Long Island, NY
    Display Name:

    Display name:
    Jordan
    Shallow out the descent. Do not climb. You’ll get way behind on the slope and end up chasing it.
     
  3. Larry in TN

    Larry in TN Line Up and Wait

    Joined:
    Nov 16, 2013
    Messages:
    926
    Location:
    Nashville, TN
    Display Name:

    Display name:
    Larry in TN
    If you're not doing it already, pitch to the G/S and use power to hold your airspeed. You'll find that you'll be able to more accurately track the G/S using that over the power for G/S technique.
     
    AndrewX and jordane93 like this.
  4. JCranford

    JCranford Pattern Altitude

    Joined:
    Mar 8, 2015
    Messages:
    2,089
    Location:
    North TX
    Display Name:

    Display name:
    JCranford
    Hold and intercept
     
    AndrewX likes this.
  5. MauleSkinner

    MauleSkinner En-Route

    Joined:
    Oct 25, 2005
    Messages:
    3,895
    Display Name:

    Display name:
    MauleSkinner
    Just as a frame of reference, at 120 knots, a 3-degree glide slope will require roughly 600 ft/minute descent.

    The glideslope, according to the AIM, is 1.4 degrees wide...I assume that's top to bottom, not from center, which makes half deflection below about 2.6 degrees, or roughly 10% flatter--about 540 ft/minute would keep it there. If you leveled off, the glideslope would center very quickly, but if you simply reduce your rate by 100-150 ft/minute, you'll get a controlled recovery back to center.

    Hope that's useful...math is better done on the ground than in the air. ;)
     
    AndrewX likes this.
  6. aterpster

    aterpster Pattern Altitude

    Joined:
    Apr 15, 2011
    Messages:
    2,103
    Display Name:

    Display name:
    aterpster
    Engage auto-land. :cool:
     
    AndrewX likes this.
  7. MauleSkinner

    MauleSkinner En-Route

    Joined:
    Oct 25, 2005
    Messages:
    3,895
    Display Name:

    Display name:
    MauleSkinner
    [​IMG]
     
    AndrewX likes this.
  8. RDUPilot

    RDUPilot Pre-takeoff checklist

    Joined:
    Feb 5, 2016
    Messages:
    309
    Location:
    Morrisville, NC
    Display Name:

    Display name:
    RDUPilot
    70B7A8FB-DDC0-4C91-873A-6D253BD13AAA.gif
     
    AndrewX likes this.
  9. Clark1961

    Clark1961 Touchdown! Greaser!

    Joined:
    Jun 7, 2008
    Messages:
    17,745
    Display Name:

    Display name:
    Display name:
    Auto-land is a bit rough in the ‘kota...
     
    AndrewX likes this.
  10. Clark1961

    Clark1961 Touchdown! Greaser!

    Joined:
    Jun 7, 2008
    Messages:
    17,745
    Display Name:

    Display name:
    Display name:
    Flying instruments is about watching and making small changes to trends. Sure ya gotta keep hard numbers in mind but ya fix the trend to stay within the boundaries and hard numbers.
     
    AndrewX likes this.
  11. AndrewX

    AndrewX Pre-Flight

    Joined:
    Nov 14, 2017
    Messages:
    63
    Display Name:

    Display name:
    Andrew
    This is very helpful. Thank you.
     
  12. Bill Watson

    Bill Watson Pattern Altitude

    Joined:
    Dec 5, 2007
    Messages:
    1,834
    Location:
    Durham NC
    Display Name:

    Display name:
    MauleDriver
    Perhaps another way of thinking about it is considering how got below the GS in the first place; you were descending too fast. So an answer is to reduce your sink rate (100_150 fpm), and to do that, a bit of pitch and power.


    Sent from my iPad using Tapatalk
     
    AndrewX likes this.
  13. rocketflyer84

    rocketflyer84 Line Up and Wait

    Joined:
    Dec 25, 2014
    Messages:
    690
    Display Name:

    Display name:
    RocketFlyer84
    For one dot would keep decending but reduce rate to catch up and get the needle centered. Trying to level off, or worse climb into it, isn’t going to work as well. If one gets so far off that a drastic move is necessary then best to go missed and have another go.
     
    AndrewX likes this.
  14. ChiefPilot

    ChiefPilot Pre-takeoff checklist

    Joined:
    Dec 1, 2013
    Messages:
    168
    Display Name:

    Display name:
    ChiefPilot
    That's way too much work. Pitch to airspeed, power to altitude. I'm trimmed to airspeed by 1000AGL and use small power adjustments to stay on glideslope. Not a whole lot of pitching to be done, unless you're into that whole chase-the-glideslope game.
     
    kgruber, pburger and AndrewX like this.
  15. midlifeflyer

    midlifeflyer Final Approach

    Joined:
    May 25, 2006
    Messages:
    8,109
    Location:
    Chapel Hill NC
    Display Name:

    Display name:
    Mark
    I have to admit that's a brand new one to me in the silly pitch vs power debate: Pitch and power is "way too much work" but power and pitch isn't? More than 20 years in online forums hearing these arguments and never heard this one before :D

    I'm pretty sure others would argue with equal certainty, that periodic light pressure on the yoke with no change of power setting, resulting in a slight change in VS and about 5 KTS airspeed is far less work and more accurate than pushing and pulling a throttle. Probably add, "if it's good enough for an autopilot and the Air Force..."

    I've seen both done and they both work. Purely a matter of technique.
     
    RDUPilot, Banjo33 and AndrewX like this.
  16. ChiefPilot

    ChiefPilot Pre-takeoff checklist

    Joined:
    Dec 1, 2013
    Messages:
    168
    Display Name:

    Display name:
    ChiefPilot
    If that's the first time you've seen a similar thing, you need to get around online more often :)

    It depends on what you're flying, I'd imagine. How pitch sensitive is a 182 vs. an RV (for example)? That makes a huge difference.
     
    AndrewX likes this.
  17. Kritchlow

    Kritchlow Final Approach

    Joined:
    Dec 2, 2014
    Messages:
    5,635
    Display Name:

    Display name:
    Kritchlow
    Lol!! Just curious.... did you mean the AP?
     
    AndrewX likes this.
  18. jordane93

    jordane93 Final Approach

    Joined:
    Sep 9, 2013
    Messages:
    8,374
    Location:
    Long Island, NY
    Display Name:

    Display name:
    Jordan
    I use Larry’s technique when I fly GA and when I fly the jet at work.
     
    AndrewX likes this.
  19. Larry in TN

    Larry in TN Line Up and Wait

    Joined:
    Nov 16, 2013
    Messages:
    926
    Location:
    Nashville, TN
    Display Name:

    Display name:
    Larry in TN
    Try your technique and note the pitch attitude both before and after the power change. You'll find that it changes. It just takes longer when you adjust the power for your G/S then let the airplane find its own pitch. Then try it my way and you'll get a faster response and will track the G/S more accurately.
     
    AndrewX likes this.
  20. labbadabba

    labbadabba Pattern Altitude

    Joined:
    Aug 12, 2014
    Messages:
    1,987
    Location:
    Lawrence, KS
    Display Name:

    Display name:
    labbadabba
    I don't pitch to G/S, but I do I pitch to the rate of descent on the VSI and then cross check my ground speed and G/S needle.

    I know at 90kts I need to be descending 450fpm at 120kts I need to be descending 600fmp. Based upon my ground speed I interpolate from there. Pegging my descent using the VSI keeps me from chasing the needle.
     
  21. olasek

    olasek Pattern Altitude

    Joined:
    Aug 17, 2009
    Messages:
    1,573
    Location:
    Oakland, CA
    Display Name:

    Display name:
    olasek
    I find the opposite to be true. It is much more difficult to make small adjustments in power than in pitch, the power technique is also a slower method, there is a delay, also this isn't technique typically taught in textbooks or by instructors.
    Le me quote from Peter Dogan classic: Once the power has been set, make glide path corrections with small pitch changes.

    Pitch to airspeed, power to altitude is the proper technique when flying small airplanes for anything except maintaining the glide path in IMC.

    But obviously you select technique which works best for you.
     
    AndrewX likes this.
  22. ChiefPilot

    ChiefPilot Pre-takeoff checklist

    Joined:
    Dec 1, 2013
    Messages:
    168
    Display Name:

    Display name:
    ChiefPilot
    I've tried both over the last couple thousand hours - they both work of course. I think both can track the GS accurately; try my way with *very* small power adjustments to maintain a desired descent rate based on groundspeed and staying on the GS becomes pretty much automatic with little if any pitch correction needed.

    Anyway, as has been said, use the technique that works best for you. I know I do :)
     
    AndrewX likes this.
  23. Larry in TN

    Larry in TN Line Up and Wait

    Joined:
    Nov 16, 2013
    Messages:
    926
    Location:
    Nashville, TN
    Display Name:

    Display name:
    Larry in TN
    I learned to fly 'your way' in the early 1980s. I learned 'my way' while a working CFI in the late 1980s. I found it worked better in the small GA airplanes I was flying then and it is the only method that works in the transport jets that I fly today.

    You can get away with the less-precise method in slower airplanes as things aren't happening as fast.

    Whichever technique is used, you need to be taught how to apply it correctly. I suspect that you've never had a CFI teach you how to use the 'power for airspeed' technique properly.
     
    AndrewX likes this.
  24. midlifeflyer

    midlifeflyer Final Approach

    Joined:
    May 25, 2006
    Messages:
    8,109
    Location:
    Chapel Hill NC
    Display Name:

    Display name:
    Mark
    Plenty "similar." The oldest post of mine I can find on the topic was September, 2000 and it looks like it wasn't my first exposure to the arguments on both sides. Just not your specific comparison of one as "way too much work" and the other barely any work at all. Personally, I haven't found a difference between them, other than personal preference, among singles from 172s and Warriors to A36 Bonanzas and Mooney Ovations

    But yours is definitely not the silliest one. My all-time favorite was when I told a story about dealing with severe windshear on short final once. But I described it in the "wrong" pitch power terms, prompting someone to seriously comment I couldn't possibly be alive if I did it that way :rolleyes:
     
    Last edited: Jan 3, 2018
    AndrewX likes this.
  25. olasek

    olasek Pattern Altitude

    Joined:
    Aug 17, 2009
    Messages:
    1,573
    Location:
    Oakland, CA
    Display Name:

    Display name:
    olasek
    I don't know what you fly but in the Cirrus that I fly tiny power adjustments are difficult, the throttle is a bit 'sticky', there is no way to adjust throttle smoothness like say in the Skyhawk, trying to make a tiny power adjustment I have to grab the throttle from below trying to finesse its position but overshooting is routine, and it is slow process. If I were to use your technique I would be flying yo-yo across the GS.
     
    AndrewX likes this.
  26. Kritchlow

    Kritchlow Final Approach

    Joined:
    Dec 2, 2014
    Messages:
    5,635
    Display Name:

    Display name:
    Kritchlow
    To be honest I don’t even think about what I’m doing. I just do it.
     
  27. Larry in TN

    Larry in TN Line Up and Wait

    Joined:
    Nov 16, 2013
    Messages:
    926
    Location:
    Nashville, TN
    Display Name:

    Display name:
    Larry in TN
    Which means that you probably don't need to ask about the best way to correct when you are too low on the glideslope. A new instrument pilot, or an instrument student, does need to ask and telling him "just do it" wouldn't be particularly helpful.

    That's when the various techniques come into play. They are used to break something complex down into smaller building blocks that can be learned and used to provide a system for accomplishing the complex task. As experience builds, the need to think about the individual building blocks will diminish.
     
  28. aterpster

    aterpster Pattern Altitude

    Joined:
    Apr 15, 2011
    Messages:
    2,103
    Display Name:

    Display name:
    aterpster
    Yes, and then some.
     
    AndrewX likes this.
  29. Kritchlow

    Kritchlow Final Approach

    Joined:
    Dec 2, 2014
    Messages:
    5,635
    Display Name:

    Display name:
    Kritchlow
    Okay... because there’s no way in the Bus to engage auto land. One just never disengages the AP.
     
    AndrewX likes this.
  30. SbestCFII

    SbestCFII Line Up and Wait

    Joined:
    Mar 27, 2013
    Messages:
    620
    Location:
    NC
    Display Name:

    Display name:
    CFII Scott
    Easy fix...don't change anything, just pitch level briefly and you'll fly right back into the glideslope.
     
    RDUPilot and AndrewX like this.
  31. AggieMike88

    AggieMike88 Touchdown! Greaser!

    Joined:
    Jan 13, 2010
    Messages:
    14,541
    Location:
    Denton, TX
    Display Name:

    Display name:
    Now offering reverse discounts.
    :yeahthat:
     
    AndrewX likes this.
  32. aterpster

    aterpster Pattern Altitude

    Joined:
    Apr 15, 2011
    Messages:
    2,103
    Display Name:

    Display name:
    aterpster
    I don't know anything about the "Bus." Do you mean there is no auto land or there is auto land, but the auto-flight system decides when auto land should be used? I flew ancient auto land airplanes; L1011 and B767. Auto land was selectable.
     
  33. Larry in TN

    Larry in TN Line Up and Wait

    Joined:
    Nov 16, 2013
    Messages:
    926
    Location:
    Nashville, TN
    Display Name:

    Display name:
    Larry in TN
    The 767 would autoland from any coupled ILS if the autopilots were not disconnected. The two additional APs would automatically engage in CMD mode in approach mode.

    On the 737 you have to manually select the second A/P (it only has two) for it to autoland.
     
  34. aterpster

    aterpster Pattern Altitude

    Joined:
    Apr 15, 2011
    Messages:
    2,103
    Display Name:

    Display name:
    aterpster
    That was a change from the early model I flew, or perhaps it was a TWA spec. We would not get auto land unless we pushed the second autopilot switch light above some agl altitude, which I don't recall. It was a minimum of 1,100 feet agl for the L1011.
     
  35. Kritchlow

    Kritchlow Final Approach

    Joined:
    Dec 2, 2014
    Messages:
    5,635
    Display Name:

    Display name:
    Kritchlow
    The Airbus does have autoland. Perhaps I wasn’t clear, but what I was trying to say is there is no “turning on” the autoland. Just keep the AP engaged and it will autoland.
     
  36. Larry in TN

    Larry in TN Line Up and Wait

    Joined:
    Nov 16, 2013
    Messages:
    926
    Location:
    Nashville, TN
    Display Name:

    Display name:
    Larry in TN
    You would have to push the second and third or just a second autopilot? That sounds like the 737 procedure.

    There were quite a few years between when you flew the 757/767 and when I did so I'm sure there were a lot of changes.
     
  37. bluesideup

    bluesideup Pre-takeoff checklist

    Joined:
    Jun 20, 2014
    Messages:
    262
    Display Name:

    Display name:
    bluesideup
    Hi.
    More details / information is required for best procedure. On a precision approach ground speed / time is important. If your ground speed / airspeed is high slowing your descent rate will do it, may need some retrim.
    If your speed is too slow some small amount of power may be needed, may need some retrim. In most cases, if you are close to target speed slowing down your descent rate will do it.
    All that said Never get below glide slope. Most examiners will fail you if you get below it.
     
  38. aterpster

    aterpster Pattern Altitude

    Joined:
    Apr 15, 2011
    Messages:
    2,103
    Display Name:

    Display name:
    aterpster
    Seemed like a second, but my last airplane was the L1011, so I tended to "bulk erase" the 767.

    The 1011 was the best for its time. Joint effort to make sure auto land met FAA demands at the time. The FAA relaxed those demands later.

    Bottom line: the 1011 exceeded the target level of safety for auto land in CAT III conditions far more than any airplane since.
     
  39. Kritchlow

    Kritchlow Final Approach

    Joined:
    Dec 2, 2014
    Messages:
    5,635
    Display Name:

    Display name:
    Kritchlow
    Never flew the 1011, but have been in the cockpit.
    Was my favorite airplane. Wish it was still around.
     
  40. aterpster

    aterpster Pattern Altitude

    Joined:
    Apr 15, 2011
    Messages:
    2,103
    Display Name:

    Display name:
    aterpster
    It comes back to me, after looking at a 767 MCP on the Internet.

    One autopilot engaged in Approach with an ILS tuned would be a non-auto land ILS. Engage the second autopilot and it was auto-land with "Land 2" annunciated (fail passive with DA). All three autopilots engaged and it was "Land 3." (fail active, with AH). I think Land 2 was amber and Land 3 was green in the EICAS.