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Thread: What causes the roll?

  1. #1

    Default What causes the roll?

    Recently, I was on a flight flown by Embraer RJ-135. The aircraft is relatively new.

    Weather was very good. But, the plane rolls left and right. I will explain. I felt the roll, so I looked outside using the horizon as reference. The left wing drops about two feet and climbs two feet back up. Of course, at the same time, the right wing would climb two feet up and then two feet down. This oscillated through out the whole flight.

    I want to call it aileron roll, but I am not sure.

    What are the possibilities? Could the pilots be constantly playing with some controls all the time during the flight? Or the ailerons were not properly trimmed? The engine output powers were not synced?

    This happened to me on an MD-80 ten years ago, but less severe.

    I am thinking, just like there is something called the automatic yaw damper, there must be some computerized automatic aileron stabilizer of some sort. Is there? That thing could have been turned OFF, or not functioning properly.


  2. #2
    Join Date
    Mar 2005
    Newcastle Upon Tyne


    Hi AA,

    I'm not really in the place to say as I wasn't there, but two feet isn't really a very large amount.

    Most aircraft do have rudder and aileron trim but, especially on the larger jets, these are just kept in the neutral position unless something goes wrong, like losing an engine, which would necessitate trimming.

    There is something called dutch roll that aircraft with swept wings and strong static lateral stability suffer from, but this is prevented by the yaw damper. I won't go into exactly what dutch roll is, why it happens and what the yaw damper does unless you want to hear about it. Anyway I doubt it was dutch roll because firstly, it would have made you feel pretty sick, and secondly, an inoperative yaw damper is almost certainly a 'no-go' or 'return to airport' item.

    Ailerons don't really have stabilising devices as such - most ailerons on modern aircraft these days are differential ailerons - the upgoing aileron moves through a larger angle than the downgoing aileron to stop a phenomenon called adverse aileron yaw - where the aircraft wants to yaw in the opposite direction in which it's banked. In addition to this, at higher speeds (usually as the last stage of flaps come up) the outboard ailerons are disabled and the inboard ailerons are used, to stop a wing twisting motion that would be caused if the outboards were still used at higher speeds. Also, most aircraft have roll control spoilers (the same ones that extend on landing - but help the aircraft to roll in the air by working with the ailerons to get a smooth, coordinated turn). Again, more on adverse aileron yaw if you want it.
    Tom - 737-800 F/O
    Win 7 x64, Q9650 @3.5GHz, 4GB DDR2, 500GB + 1TB SATA2, 1GB HD 6870

  3. #3


    Just a guess but it might be the autopilot levelling the wings whenever a bit of minor turbulence is around

  4. #4
    Join Date
    Feb 2009
    Murfreesboro TN when at school, St. Louis when home


    possible it was an AP malfunction. Also could have been windshear or CAT, if i knew the flight route and wx i could tell better.
    FAA Certified Aircraft Dispatcher

  5. #5


    Thank You Tom for taking the time and explaining. Thank You SBK. Thanks T18.

    After more reading, I tend to lean towards describing the matter as dutch roll. That would be the closest if not the exact name.

    Funny thing is -- the weather was as good as it gets. Visibility was so good I saw everything on the ground from 18K from take off to landing. There was barely any wind. The aircraft should not shake, roll, drop, or vibrate. That was a more than a perfect day to fly. That ERJ-135 just rolled non-stop.

    If the equipment was very new, and most likely to be flawless. I am thinking the inexperienced crew could be new to this type. Commercial airlines do put the newest pilots on the RJs. Uh, I take this back. I forgot the turbo-prop drivers.


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