What does a red radial line on an airspeed indicator indicate?

The red radial line on an airspeed indicator signifies the never-exceed speed (Vne). This is a critical speed that pilots should not surpass under any circumstances, as exceeding it could lead to structural failure of the aircraft. The red radial line serves as a visual warning; if the aircraft's speed crosses this threshold, it introduces severe risks.

Understanding the significance of Vne is vital for ensuring flight safety. Each aircraft has specific limitations, and the Vne represents the point beyond which the aircraft's structural integrity could be compromised due to excessive airspeed. Therefore, maintaining awareness of this indicator is crucial for pilots in managing their flight operations within safe parameters.

The other choices refer to different aspects of speed indicators. Normal operating range typically involves green markings, while stall speed is represented by a different colored line, often yellow or a specific marker, depending on the aircraft's design. Maximum landing speed is usually indicated elsewhere and is not represented by the red radial line. Thus, the red radial line clearly and specifically denotes the critical speed limit that must not be exceeded.