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Thread: Question to Boeing Bobby: PIO

  1. #1
    Senior Member 3WE's Avatar
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    Default Question to Boeing Bobby: PIO

    It's an acronym we like to drop.

    It's also a real thing that occasionally rears it's head and breaks airplanes.

    I have experienced the ground version on my bicycle, my Toyota station wagon, and experienced it more than once in a 172.

    I have seen it happen you youtube to tail draggers.

    I seem to recall the occasional Lear Jet crash, we have the DC-10 at Narita, and we have the recent Russian crash.

    My questions are pretty basic:

    Are there truly nasty airplanes that if you get behind, a person is likely to experience a PIO?

    Is the secret "only" to stay ahead of the airplane?

    OR

    Are there some good universal rules to "almost always" nip a PIO in the bud.

    Is a PIO incident a reflection of a crappy pilot or crappy performance?

    Also, I'm more interested in PITCH oscillations than tail-dragger oscillations.

    And, I'm looking for broad information as opposed to a statement that it would not happen to you.

    Footnote: There was a theory that the FedEx-Narita pilots were tricked by a cockpit height visual cue that they were on the ground, but nose-wheel up- when in fact the rear of the plane was rising with a simultaneous nose over to a hard landing...(I guess they SHOULD have checked the AI, but hey, it was a busy landing with tired folks and first class wind).

    Thanks.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    Senior Member Evan's Avatar
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    Quote Originally Posted by 3WE View Post
    we have the DC-10 at Narita...
    MD-11. Sorry to butt in but that goes with the part that says...

    Are there truly nasty airplanes that if you get behind, a person is likely to experience a PIO?
    MD-11. Maybe not "nasty" but it had a... reputation... for being ornery in a crosswind flare...

    Carry on.

  3. #3
    Senior Member 3WE's Avatar
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    Yes- Bigger airplane + smaller "elevator"...Scientifically engineered to take advantage of "lever-mechanical-advantage".

    Quote Originally Posted by Evan View Post
    ...reputation...
    Said word has the implication that it may or may not be true.

    The purpose of the post is to seek some inside information if there are solid procedures other than don't get behind the airplane.

    You land a super jet 100 times...but booger up one little aspect and you're achieving your 90 day currency (3 landings) in once approach.

    Bad day or bad airplane? (when in alternate law)
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    Senior Member BoeingBobby's Avatar
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    If it's a PIO, it's pilot induced. Hence the P. But I am pretty sure that it's probably Boeing's fault.

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    Senior Member 3WE's Avatar
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    Quote Originally Posted by BoeingBobby View Post
    If it's a PIO, it's pilot induced. Hence the P. But I am pretty sure that it's probably Boeing's fault.
    1. Expeletive-laden, ban-worthy, personal flame attack for an evasive answer.

    2. A crap eating grin.

    3. Noted.
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    Senior Member BoeingBobby's Avatar
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    I have never flown a Douglas jet aircraft, DC-3's and DC-6'S were the only ones. I have seen and heard the stories about the DC-10 and MD-11 but that only gives me the same insight as you. I have been in DC-3's and C-46's where a bounced landing has resulted in PIO. I can't think of any airplanes that I have flown that are more susceptible. The old Piper Twin Comanche was a floater and was hard to get a consistent smooth one out of it. The one we had lots of fun with was PIT!

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    Senior Member 3WE's Avatar
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    Also Noted.

    Thanks.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    Senior Member Gabriel's Avatar
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    Now that BB's satisfied your questions, I will chime in.

    I've never seen PIO recovery mentioned in manuals, I've never heard of PIO being taught in training or practiced in sims or real training flights.

    But there is a "standard way" to deal with PIO (or oscillations in general) which is: command for rate, not position.
    That was easier to say and it is harder to do but here is how it works (and not it becomes easier to do than say):

    1. Define the target value of the parameter you want to control (pitch in this case)

    2. Define a target rate (doesn't need to be some exact number, just how fast you want the parameter you want to control, pitch in this case, to change, but it can be in terms of how it feels rather than say 1.5 degrees per second).
    2a. When you want to stop PIO, your initial target rate should be zero unless there is a daring situation for it to be another thing. Once you achieved zero rate, and hence are not in PIO anymore, go to 2b.
    2b. When out of the PIO, or if an initial target of zero rate is not possible, define your target rate in function of the difference between the actual and target value of the parameter you want to control, with a max cap. Again, this doesn't need to be a scientifically defined number, just it have to feel good but you need to know that your target rate must decrease and become zero as you approach the target value of the parameter.

    3. Apply controls to enforce the target rate. Note that this may be applying nose down inputs when you still want to pitch up more (but you want to decrease the pitch up rate because you are closing to the target pitch).

    4. Periodically re-evaluate 1 and re-define 2 accordingly.

    Applying this could have saved a few accidents. mong them, the AA A300 rudder-happy one for sure, possibly the MD-80 flapless take-off at Detroit too.

    Note that something similar to this is everyday's job when for example tracking the glideslope. Say you are high so you want to get closer to the center but not too fast. You don;t just push down. You know that your target vertical speed to keep the glide slope is say 700 fpm (it's the ground speed divided by 2 and add 1 zero, so if you are doing 140 ground your target is 700), and perhaps you are doing 700 but that will not take you down to the glide slope, so you define a new target of say 1000 fpm. But you just don't push down chasing for the 1000 fpm. Rather you say "let's go down 1 degree in pitch" so you now push down to adjust the pitch and keep it at the new target. Then see if that gave you about the desired 1000 fpm and re-adjust the pitch if not, then you check the speed of the ILS needle to see if it is coming to the center and if it is doing that too slow or too quickly, and re-adjust your vertical speed target based on that, for which you re-adjust your pitch. Of course, experience and practice can help better define the targets and better use the controls to reach these targets.

    Pilot's may say that no way they do that. They don't realize it, it's natural, almost instinctive, but that's what they do. What's the alternative? Chase the ILS needle? Chase the vertical speed? That quickly becomes in sewing the ILS and the vertical speed. (i.e. PIO)

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    Senior Member BoeingBobby's Avatar
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    My rule of thumb in anything other than a general aviation aircraft, more than a little bounce, GO AROUND and try again.

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by BoeingBobby View Post
    My ruel of thumb in anything other than a general aviation aircraft, more than a little bounce, GO AROUND and try again.
    Why "other than a GA airplane"? (honest question)

    https://www.youtube.com/results?sear...=porpoising%3F
    https://www.youtube.com/watch?v=x5ZzktAFJK4
    https://www.youtube.com/watch?v=4rwhaHIQrcU
    https://www.youtube.com/watch?v=G9FkYpvTyrc
    https://www.youtube.com/watch?v=wszJqh_5wqc

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    Senior Member Gabriel's Avatar
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    And I want to make a point that porpoising, if you can call it PIO, be my guest, but is a totally different kind of oscillation than the regular PIO where the pilot inputs get in phase with the airplane dynamics. Porpoising can happen with the pilot keeping the control column fixed in one position. While there are techniques to recover (basically, hold a nose-up landing pitch attitude instead of push down to try to keep the nose gear on the floor), the best one is what BB said.

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    Senior Member BoeingBobby's Avatar
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    Because in a little airplane, you can probably save the landing. No one asked about porpoising.

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by BoeingBobby View Post
    No one asked about porpoising.
    Well, while factually true, I took 3WE's question in the context of the Superjet accident which looks like porpoising, and he mentioned the FedEx MD-11 accident which was due to porpoising.

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
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    Quote Originally Posted by Gabriel View Post
    Well, while factually true, I took 3WE's question in the context of the Superjet accident which looks like porpoising, and he mentioned the FedEx MD-11 accident which was due to porpoising.
    Even more factually, Gabriel, nobody asked YOU anything.

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    Quote Originally Posted by ATLcrew View Post
    Even more factually, Gabriel, nobody asked YOU anything.
    Whoa!

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by ATLcrew View Post
    Even more factually, Gabriel, nobody asked YOU anything.
    A lot of us were not asked anything, flyboy. In fact, all if use but BB.

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
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    Quote Originally Posted by BoeingBobby View Post
    Whoa!
    Just the facts.

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    Senior Member BoeingBobby's Avatar
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    Quote Originally Posted by ATLcrew View Post
    Just the facts.
    And nothing but the facts.

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    Senior Member brianw999's Avatar
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    Facts which have nothing to do with the direct subject. This is getting too personal.
    If it 'ain't broken........ Don't try to mend it !


  20. #20
    Senior Member 3WE's Avatar
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    Maybe a little personal, but within the realm of normal and with some factual correctness on all sides.

    Some more facts:

    Gabe, you did kind of blow in spewing lengthy pontifications inferring a grand expertise...kind of.

    Yes, this was relevant to Moscow- and Porpoising is an oscillation that a pilot can induce...

    AND, I suppose there are aircraft and flight modes prone to oscillations.

    As to Gabriel's 4-step process, I say bullcrap for practical use. Sure, it's theoretically valid, but your thousand or so Super jet landings have never ever gone bouncy before, but you get hit by lightning and I've heard the term "alternate law" invoked...I kind of doubt you can train using your method to instantly nip the landing in the bud.

    Bobby did give a good answer- "THE" solution is probably something along the lines of DO NOT nose over and be liberal with the coal lever. I suppose another method is to be hyper sensitive to attitude and try to "lock" the plane in a healthy nose up attitude and either fly it away or fly it back down.

    And, it does appear there is no formal PIO training...(and it appears 172's are prone...I will tell you as a dumbass student pilot, when TWO folks got out for my first solo...the aeroplanie was more bouncy.)

    Getting back to the Moscow crash- I am wondering if the spoilers deployed to properly to kill lift and prevent bouncing...not sure I have seen them or not in the various films.

    Peace, Love, Flamings, Humor, and a small shred of aviation knowledge.
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