MD-90 Pitch Oscillation

[pulse1]

Since BA have dropped some of their Scandinavian flights I am using SAS and the MD-90 a lot more.

Sitting in row 22 on a recent flight to Sweden, I experienced an unpleasant, regular pitch oscillation (+/- g. every 1 - 2seconds)during the cruise phase of the flight. I have never felt this in any other aircraft and have sat in most areas of most common airline types over the years.

Is this normal for the MD-90 or does it indicate poor trim or some other more worrying problem? I must say that it did cause the Alaskan stabiliser failure to cross my mind.

I'm off again next week so, if this is normal, I will try to sit further forward (jump seat would be good
:) ).

[Wino]

You were most likely flying through an area of wave activity. Common in the winter when the jetstream starts to blow. Suprisingly low hills and mountains can send the waves well up into the atmosphere (35000 feet). The crew will see on their guages increasing and decreasing airspeed along with the vertical speed indicator cycling up and down.

It can be minor and annoying (like you experienced) or the precurser to getting the snot kicked out of you...

Hope it helps
Cheers
Wino

[pulse1]

Wino,

Thanks very much for your suggestion. You could well be right. Assuming that we were travelling at 90° to the wave, that would make the wave length about 0.25 - 0.5 miles. Is that reasonable? What is a typical wavelength for wave? I have always imagined that it would be much more than that. I am not sure where we were but, based on timing, I guess we were just crossing the east coast of the UK, about 200 miles downwind of any serious hills.

My only experience of wave is in gliders or light aircraft at much lower altitude and, of course, much slower.

[AutoAbort]

Nothing to be concerned about. Enjoy your next flight.