Plain English Meaning

It's the absolute top speed the aircraft is allowed to fly. Going faster than this can break the airplane, even in calm air.

Full Definition

Redline speed is the never-exceed airspeed for an aircraft, marked by a red radial line on the airspeed indicator. It represents the maximum speed at which the aircraft may be operated in smooth air; flying faster than this risks structural damage or failure from aerodynamic loads, flutter, or control surface stresses. On the Vg diagram, redline speed is the right-hand boundary, beyond which the aircraft is no longer guaranteed to remain structurally intact even at low load factors.

Context Anchor

Seen on the airspeed indicator and in Vg diagram discussions about the airplane’s speed and limits.