Plain English Meaning

A speed worked out by taking the slowest speed at which the airplane can still fly with gear and flaps down, then multiplying it by 1.8. It sets a sensible upper limit for how fast a small airplane should fly during an instrument approach.

Full Definition

An airspeed equal to 1.8 times the airplane's stalling speed in the landing configuration (gear and flaps extended). For small airplanes, this is the maximum airspeed at which an instrument approach should be flown unless the airplane is being operated at a higher airspeed for a specific reason.

Context Anchor

Seen in discussions of slow-speed flight, approach speeds, and small-airplane handling near the lower end of the speed range.

Derivation

VSO comes from V () and S (), with the O meaning 'in the landing configuration' (gear and flaps fully extended). The 1.8 is simply a — 1.8 times that .