This glossary is written for virtual airline and flight simulation use within Virtual Air Canada Airline. It is not intended as a real-world aviation reference.
MMo
Maximum Operating Mach Number
Maximum Operating Mach Number is the highest Mach number at which an aircraft is certified to operate, representing an upper speed limit defined in the Aircraft Flight Manual. MMo applies at altitudes where Mach number rather than indicated airspeed becomes the limiting factor - typically above the crossover altitude where the aircraft would reach VMo (Maximum Operating Indicated Airspeed) and MMo simultaneously. Exceeding MMo risks entering the region of compressibility effects, including Mach tuck, control buffet, and reduced control effectiveness caused by the formation of shock waves on the wing and control surfaces.
Transport aircraft are designed with a margin between MMo and the speed at which handling characteristics degrade significantly (known as Mmo buffet or upset onset speed). The aircraft’s overspeed warning system will trigger aural and visual alerts if the crew allows speed to exceed MMo, and the autopilot autothrottle system normally prevents the aircraft from reaching this limit in normal operation. On aircraft with flight envelope protection systems, such as Airbus fly-by-wire types, hard limits prevent the aircraft from exceeding MMo under computer control. Typical MMo values for common commercial transport aircraft range from Mach 0.82 for narrow-bodies to Mach 0.89 or higher for some wide-body types.