Sure, but it is more relevant to describe aerodynamic properties of an aircraft. Knots can have a similar problem (look up indicated airspeed). But I guess you’

Sure, but it is more relevant to describe aerodynamic properties of an aircraft. Knots can have a similar problem (look up indicated airspeed). But I guess you’re right, we should be using ground speed knots in this instance. If you ask a pilot, ground speed only really is important for calculating ETA. Everything relevant to flying is a relative number since atmospheric density is fluid.