I have experienced AW139 nose-wheel shimmy on two occasions and it is undoubtedly an unfortunate design quirk in the nose-wheel steering. It is loud and frightening if you have never experienced it before and I know of one occasion where an inexperienced pilot thought he was entering ground resonance and lifted (AP Out) to stop the shimmy. The frequency of the shimmy is about 0.25 of a second and is felt as a 'jarring' throughout the airframe, if you look behind the aircraft you will see a tell tale herring bone pattern of marks left on the taxiway or runway. On both occasions when it happened to me it was because the nose-wheel "slipped off" a raised dome centre line light, landing at a slight cross angle to the aircraft direction. I have no reason to suspect that it is associated with incorrect taxi techniques and I was able to stop the shimmy by using wheel brakes. On both occasions I had the engineers confirm that there was no damage before proceeding. I now ground taxi slightly offset from any centre line that has embedded lighting.
Last edited by Max Contingency; 12th Apr 2013 at 22:53.