overspeed

Overspeed refers to the operation of a device, vehicle, or system at speeds beyond its designed maximum, such as an airspeed limit, engine RPM, or rotor speed. It can result from external conditions, control faults, or misoperation and is generally associated with increased mechanical stress, structural damage, or component failure. To prevent damage, many systems include automatic protections that limit speed or shut the equipment down if limits are approached or exceeded.

In aviation, overspeed most commonly means exceeding the maximum operating speed, such as Vmo (or MMO when expressed in Mach) in flight. Surpassing these limits increases aerodynamic loads and can lead to structural damage, flutter, or engine instability. Aircraft employ overspeed protection through flight control logic, throttle limits, and, in some designs, automatic protections that prevent further acceleration or trigger a safe mode.

In internal combustion engines and road/rail vehicles, overspeed occurs when rotating components exceed their rated maximum RPM, often called the redline. This can cause valve float, bearing or piston damage, and fatigue in rotating parts. Modern engines use rev-limiters or governors to cap speed, and some systems automatically reduce fuel delivery or disengage power if the limit is approached.

In marine and industrial contexts, propulsion and power turbines are equipped with governors or electronic limiters to prevent overspeed, trip protection, and shutdown sequences if RPM rises too high. Wind turbines use rotor overspeed protection—via pitch control, mechanical brakes, or aerodynamic braking—to keep rotor speed within safe bounds under high wind.

See also: redline, speed limiter, governor.