Why did my commercial flight roll back and forth for 20 minutes?


No turbulence. Blue sky above. Sea of clouds below. Straight flight from Houston to Wichita in Embraer 145.

Cruising at altitude, very smooth.

This was very subtle, but I had my head planted against the window and watched the winglet for about 20 minutes. It appeared to dip down into the clouds a few degrees, hold for 5 seconds, then rose into the blue sky a few degrees.

It always went up and down the same exact amount and for the same duration.

Was it adjusting for crosswind? If so, why not use the rudder? (Not a pilot, just curious)

In: Technology

I think this can happen if there is unexpected air traffic, flights coming in early or late etc…

I think you noticed Dutch Roll, especially if you were in the back of the plane. Roll, normally controlled by the ailerons, and yaw, normally controlled by the rudder are aerodynamically interlinked, and they create a feedback loop which leads to a constant roll oscillation, which is subtle as long as it’s counteracted. Larger aircraft have a yaw damper feature of the autopilot which auto-controls the rudder to counteract this oscillation. Being high and slow makes it worse.

It was first identified by an aeronautical engineer in 1918 (quote from [Wikipedia](https://en.wikipedia.org/wiki/Dutch_roll)). “Dutch roll – the third element in the [lateral] motion [of an airplane] is a yawing to the right and left, combined with rolling. The motion is oscillatory of period for 7 to 12 seconds, which may or may not be damped.”

This is maybe beyond explaining to a 5 year old but I tried 🙂