Is nosewheel shimmy common on the 139?
I saw a quite extraordinarily vigorous nosewheel shimmy on a swift-taxying 139 a year or two ago. The pilot(s) soon quelled it by very apparently tromping on the brakes, but it was a very vigorous shimmy for a second or two.
Is there a maximum groundspeed for taxying? Is there an annunciator or audible warning for an exceedance of such a limit?