VMO

Vmo stands for maximum operating speed. It is an aircraft’s upper limit for indicated airspeed during normal flight, defined by the manufacturer and approved by aviation authorities. The Vmo value is expressed as knots of indicated airspeed (KIAS) and represents the speed beyond which continued flight could cause structural damage or unsafe handling.

The Vmo is not the only speed limit a pilot must observe. As altitude increases, the governing speed can shift from a purely indicated-airspeed limit to a Mach limit, known as MMO (maximum operating Mach number). The effective speed limit is the lower of VMO or MMO, and in many aircraft this combined limit is referred to as VMO/MMO. When either limit is reached, speed-limiting protections and cockpit indications help prevent overspeed. In practice, pilots monitor airspeed on the instrument panel and ensure profiles stay within the approved envelope throughout the flight.

Vmo values vary by aircraft type and certification. Light general aviation airplanes typically have lower Vmo values, while commercial airliners set higher limits that remain sensitive to altitude because air density and compressibility change with altitude. The Vmo concept complements other airspeed designations such as Vne (never-exceed), Va (maneuvering), and Vfe (flap operating), all of which help define safe operating boundaries for different flight regimes.