When Not to Aim for the Numbers

Discussion in 'Pilot Training' started by Niladri, Dec 17, 2009.

  1. dmccormack

    dmccormack Touchdown! Greaser!

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    We're in violent agreement. I haven't disagreed with any of your posts in this thread, and most (probably all?) of my flying is right in line with the Lycoming advisory.

    But Ron brought it up as a subtext to the stabilized approach discussion, arguing that a "powered approach" was required by the FAA, and that power to idle abeam the numbers would contribute to premature wear.

    As others have ably mentioned, the 50F/min cooling rate isn't always concomitant with a power off approach, and being overly kind to the engine to the detriment of proficiency is penny wise, pound foolish.
     
  2. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Agreed, but I don't think anybody suggested doing that.
     
  3. poadeleted20

    poadeleted20 Deleted

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    What's required by the FAA is the use of power to control glide path on one task of the practical test. You can't make a truly power-off approach that way.
    ...and I stand by that statement based on the CHT cooling rates I've seen on power-off approaches and Lycoming's published statements.
     
  4. dmccormack

    dmccormack Touchdown! Greaser!

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    I must be dense, Ron, cause I just don't see where, precisely, a powered descent is a requirement of a stabilized approach?

    Again -- I'll be clear to define a "power off" approach is power to idle, with momentary, minimal increases of power from idle to maintain the desired glidepath and speed.

    This is came up with one of my students on his practical -- I taught him to use full flaps and set MAP to 14" or so until the field was made, then power to idle.

    The DE complained that it "makes the approach too steep."

    Hunh? Since when is that a requirement??
     
  5. poadeleted20

    poadeleted20 Deleted

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    The use of power to maintain glide path is part of that stabilized approach. If you make a power-off approach, you are using something other than power to manage glide path. If you use power changes to adjust glide path, you're not making a "power-off approach" as the FAA uses that term. There's nothing to say you can't use idle power as your baseline and add power as needed if you go low, but if you go high, you'll have to use something other than power to compensate, and slips and configuration changes on final are not part of a stabilized approach. That's why it's a lot harder to fly a stabilized approach starting at idle power than at some higher setting.
    That's not the FAA's definition -- they define a "power-off" approach as one in which the power is reduced to idle abeam the touchdown point and left there until after touchdown. See the Commercial PTS for the 180-degree power-off approach task. That's how the FAA wanted "normal" approaches to be made back when I learned to fly in 1969. If you had to add power to make the runway, that was a ding against you on the checkride. OTOH, holding back some flaps so you could add drag in close to get down, or slipping, was perfectly OK on "normal" approaches. They changed to recommending the stabilized approach in the 1970's.
    That's not a stabilized approach as the FAA defines it, so I can see why the examiner was not happy.

    It would appear that our differences involve semantics -- you have a definition of "power-off approach" which differs from the FAA's, and I am using the FAA's definition.
     
    Last edited: Dec 22, 2009
  6. dmccormack

    dmccormack Touchdown! Greaser!

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    No, you're interpreting the FAA language to mean "some amount of power above idle."

    As far as the DE complaining about the approach being "too steep," how the heck can that be a valid complaint if the airplane was maintaining a steady glideslope and maintaining the specific airspeed (in the case of that airplane, 1.3xVso)?

    Consider: Airplane A is stable at 4 degree slope, power set to 60% all the way to just before touchdown.

    Airplane B is 45% power at 5% slope all the way to touchdown.

    What's the difference, as far as the FAA Definition is concerned?
     
  7. poadeleted20

    poadeleted20 Deleted

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    If you can fly a power-off approach without adding "some amount of power above idle" and still maintain a stabilized approach and steady glide path all the way to the flare, you're a better man than I am, Charlie Brown. My power-off approaches involve varying flap settings, use of slips, and changing speed to use L/D to manage glide path. That's not stabilized.
    If the power was initially kept at 14" and then cut to idle at some point, there is going to be a big change in glide path when that cut is made. That's not a stabilized approach.
    Nothing, but I'd like to see someone fly an approach at any power setting without touching power or using pitch, slips, or configuration changes to control glide path. I'm sure that under some unusual conditions it can be done by an extraordinarily skilled pilot, but that's a special case.
     
    Last edited: Dec 22, 2009
  8. PittsDriver

    PittsDriver Cleared for Takeoff

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    Not better, just practiced up to an acceptable level of proficiency. Our engines are ready to explode but we're at least practiced. ;)
     
  9. poadeleted20

    poadeleted20 Deleted

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    Oh, humbug.
     
  10. PittsDriver

    PittsDriver Cleared for Takeoff

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    If I assume you mean all that and hit a spot then it's pretty impractical given all your qualifiers. But I don't see the relevance of that test - conditions are constantly changing, wind most of all. Unless all my controls got locked up when the engine failed why would all those qualifiers be at issue? If that happened, I'm using the 'chute anyway and then the airplane is coming down with all that stuff you said.

    Power on approaches are easier to fly and easier to learn because you've been given another tool - power. The FAA recommends this method because someone there felt it was safer to fly that way (engines rarely fail). In the interest of never being satisfied with my airmanship and constantly striving for higher levels of skill, I think I'll keep on practicing my emergency power off landings with some regularity to stay proficient. If an DE wants to see something else, I'll show them that too.
     
  11. PittsDriver

    PittsDriver Cleared for Takeoff

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    Ron, that's the funniest thing I've ever seen you post! :D:D:D
     
  12. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    It's still possible to fly a power-on approach in a single and maintain within gliding distance of the runway. That's one thing I teach students to do.

    In a twin, I worry less about it, and focus more on a stable approach that keeps pax happy. If I'm in the pattern and an engine fails, I can make it to the field on the other one.
     
  13. dmccormack

    dmccormack Touchdown! Greaser!

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    Hunh? Did you mean power-off?
     
  14. dmccormack

    dmccormack Touchdown! Greaser!

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    Let's take a ferinstance...

    I have a grand total of 65 horsepower, no flaps, and trim.

    2550 RPM is max, 2300 is cruise. 1000 RPM is idle.

    Once I have the runway made (which means I will land on the runway if I lose all power), I reduce power to idle (1000 RPM).

    The airplane's descent rate increases if speed is maintained at 60 MPH.

    Once 20' AGL or so the descending glide becomes a near-level glide, further reducing speed. Now that the airplane is slower, "idle" RPM is 900 or so.

    Then I hold it off until all three wheels gently touch (38 MPH or so).

    Is the approach "stabilized?"

    Sure!

    Is is a straight line with no variations?

    Of course not!

    Well, what about an ILS?

    That's a powered approach meant to maintain a very shallow (3 degree) descent.

    Not the same exercise.
     
  15. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Nope, power-on. You'll really feel like an idiot if you were within gliding distance of the runway, fly a 747 pattern, and your engine quits when you get out of gliding distance.
     
  16. Fast n' Furious

    Fast n' Furious Line Up and Wait

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    Don't you guys have some Christmas shopping to do or something?

    Please Santa...bring this thread a DNR certificate soon. Any color...any size. :)
     
    Last edited: Dec 22, 2009
  17. Niladri

    Niladri Pre-Flight

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    Last edited: Dec 22, 2009
  18. dmccormack

    dmccormack Touchdown! Greaser!

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    If you're within "engine's dead gliding distance" then by definition you don't need power to make it to the runway.
     
  19. dmccormack

    dmccormack Touchdown! Greaser!

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    Nope -- all done! Just gotta wrap the stuff!:yesnod:
     
  20. drizzt76

    drizzt76 Pre-takeoff checklist

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    Wow, all this "landing with power off/idle" makes we rethink how I'm landing. I land with power all the time.... I guess I could try landing with the throttle rolled back at idle but it would be a waste of time because it takes a little time for the rotor to get back up to speed to hover away. :)
     
  21. Everskyward

    Everskyward Administrator Management Council Member

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    :rofl:
     
  22. Larryo

    Larryo Pre-takeoff checklist

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    Read the language, there is an option if it is not a stabilized approach, so what do you call it?
     
  23. Larryo

    Larryo Pre-takeoff checklist

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    We'll have to just disagree on this one.
     
  24. dmccormack

    dmccormack Touchdown! Greaser!

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    Burden's on you, but I don't think a barrel roll on final is "stabilized" for the purposes of the Private Pilot PTS.

    Now, I'll agree with you that "stabilized" is the same as "coordinated" -- situation, airplane, and pilot dependent.

    For example, staying high on final in case the engine quits, slipping in so you can see the runway over the nose, and kicking it straight just before touchdown might be "stable," as you flew the approach as planned and there was never any doubt as to the outcome.

    Of course this doesn't meet the FAA's quasi-definition, but I think that's the crux of this entire thread: There's a definition imposed by the practical test standards -- which are not as clear cut as some would have you believe, since there's the further narrowing caused by individual interpretations of CFIs, DPEs, and the rest.

    Then you pass the test and are released into the big bad world of ambiguity. Some are more comfortable with that than others.
     
  25. poadeleted20

    poadeleted20 Deleted

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    Yes, it is, but it's not easy, and you can't at all if you're behind anyone not doing the same thing unless you already have a lot of space behind them.
     
    Last edited: Dec 23, 2009
  26. dmccormack

    dmccormack Touchdown! Greaser!

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    Recomending which technique?

    ("power-on approach in a single and maintain within gliding distance of the runway") means what, precisely?
     
  27. poadeleted20

    poadeleted20 Deleted

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    Maybe in your mind, but not by the FAA's definition quote above.
     
  28. dmccormack

    dmccormack Touchdown! Greaser!

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    Good grief, Ron -- admit it -- it's your interpretation of a supposed FAA "definition"

    :mad2:
     
  29. poadeleted20

    poadeleted20 Deleted

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    The FAA looked at that issue, and found there are very few instances any more of engine failures in the traffic pattern leading to accidents. OTOH, they found many, many landing accidents resulting from unstabilized approaches. That's why they don't stress remaining in gliding distance as much any more, and do stress making stabilized approaches.
     
  30. poadeleted20

    poadeleted20 Deleted

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    You do if you have removable drag. If you have half flaps and partial power and lose the engine, retracting the flaps and going to max L/D speed can change the aerodynamic L/D enough to make up for the engine loss. Nothing will help you in that case if you get strung out four miles following other traffic, but in a "normal" traffic pattern it may make the difference. The trick is knowing how to pitch the plane while retracting the flaps so you don't sink.
     
  31. poadeleted20

    poadeleted20 Deleted

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    The FAA put it in black and white, and I quoted it, and gave you the link. Nothing "supposed," and no interpretation necessary. Just read it.
     
  32. dmccormack

    dmccormack Touchdown! Greaser!

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    I read it -- a while before you posted it, and took it for what it was worth -- an expectation that the approach would not include large excusrions from an ideal glidepath or airspeed once the turn to final is made.

    Unless I'm not comprehending, it appears that you are are adding the requirement that a "stabilized approach" include power (how much? who knows) and that a slip cannot not be accepted as "stabilized."

    So how do you fly a stabilized crosswind landing??
     
  33. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Having other people in the traffic pattern screws everything up, yes. I was referring to times when you're the only one in the pattern (which is most of the time at the airports I fly at). Sorry for not clarifying.

    I'd believe that, and it makes sense. Another one of those "it depends" things, though.
     
  34. poadeleted20

    poadeleted20 Deleted

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    Dan, you're going to have to find someone else to nitpick. I've been successfully training pilots for over 35 years doing it the way the FAA says they want it done in that pamphlet and their handbooks and the PTS. If you think you have a better way, you do it, and good luck.
     
  35. dmccormack

    dmccormack Touchdown! Greaser!

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    OK, so no answer then. :rolleyes:
     
  36. PittsDriver

    PittsDriver Cleared for Takeoff

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    Can someone post the link to the definition of a stabilized approach again so we don't have to read back through 190+ posts to find it. I've always taken a stabilized approach to mean that the airplane is doing what I want it to, how I want it to do it, and I'm well ahead of what's about to happen next. Where does it say, who's interpreted it, ruled on it, or whatever that says a forward slip to land at no power isn't a stabilized approach? When I do it, I'm going something I've done thousands of times, can hit my spot in some pretty demanding gusty winds, and the there's no moment when I'm making huge corrections for oscillations or other things that someone could interpret as "unstable." It might look like something crazy to someone who's million times around the pattern are "by the numbers" but it's completely controllable and stabilized in all respects. It doesn't take a super pilot to do this - just practice to develop the skills.

    But all that crap I just said is my own interpretation of "stabilized." Is there anything anyone can point to other than internet forum opinion that says anything different?
     
  37. dmccormack

    dmccormack Touchdown! Greaser!

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    Agreed. Here's where the problem lies (lay?):

    FAA Order 8400.10 defined a stabilized approach as "Maintaining a stable speed, descent rate, vertical flight paths, and configuration." The paragraph also stresses the importance of a stabilized approach stating, "Operational experience has shown that the stabilized approach concept is essential for safe operations with turbojet aircraft, and it is strongly recommended for all other aircraft."

    Sure, for turbine aircraft. And this order is now rescinded.

    AC 91-79, Runway Overrun Protection also defined a stabilized approach as "l. Stabilized Approach Concept. The stabilized approach concept is one in which the pilot establishes and maintains a constant angle glide path, towards a predetermined point on the landing runway. It is based on the pilot’s judgment of certain visual cues, and depends on establishing and maintaining a constant final descent airspeed, a constant descent rate, and a specific aircraft configuration."


    From 8900.1 Section 5 Surveillance of a Certificated Flight Instructor

    From 8900.1 change 1:
    However, these criteria are for turbine aircraft or aircraft operating in instrument conditions.

    Certainly, the argument can be made that habits formed flying little planes will serve well flying larger, more complex airplanes.

    But slavishly adhering to procedures meant for large, complex airplanes in little airplanes may be counter-productive.

    We wonder why C152s fly 4 mile finals?

    Easy -- slavish insistence on powered approaches with shallow glide angles. It certainly makes it easier to learn to land since the changes in pitch attitude are less severe and the runway is visible longer.

    Sure, every once in a while some old timer will whack a student and tell him to "keep the field close in case you lose the engine," but that advice is passe, yesterday's news, old guy talk -- bah! Today's engines are flawless!

    Ok.
     
    Last edited: Dec 23, 2009
  38. el con

    el con Line Up and Wait

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    Most of the GA engines today are pretty much the same as they were for the last fifty years,right?? And still a common problem is the engine quitting when it's out of fuel, best engine in the world still fails to make power without fuel, might still be a good idea to stay a little high in my oppinion . I think I'd rather have to slip in a little" unstable" instead of lifting my feet hoping I get to the runway. But then again I'm new to this.
     
  39. Everskyward

    Everskyward Administrator Management Council Member

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    Hmmm... I think maybe carrying a little more fuel might be a good idea too. :idea:

    I think you should be able to do both. All these people who routinely do power off (idle) approaches from abeam the numbers must fly at airports without much traffic.

    Geez I actually responded to this thread...
     
  40. Lance F

    Lance F Pattern Altitude PoA Supporter

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    and I've been expecting it to be locked for a long time. :rolleyes: