Originally Posted by Re-Heat
I always thought that many speed limits were the limits at which significant damage to the structure could start to occur - clearly structural failure rarely happens immediately at any operational speed, and flying up to published limits would not break the aircraft at that point in time, but result in many structural repairs to prevent eventual failure at a later date under normal operating conditions??
That is one limit. Maneuvers may lead to excessive airframe loads above VD/MD, which is the limit where maneuver loads have to be calculated and the maneuver loads above VD are tghus not accounted for. It is generally not recommendable to give maximum rudder at those speeds (while most likely will not lead to structural failure if it is applied with some respect).
Another problem would be gust, which can be quite challenging for the airframe at such air densities.
I would assume that for "good" configuration (lots of weight in the wings) and careful handling the VMO can be exceeded by a fair margin at low altitudes. Weather should be corresponding.