What does an underlined speed or altitude represent?

An underlined speed or altitude indicates a minimum threshold that must be adhered to during flight operations. This visual cue serves to ensure that pilots maintain a specific level of performance, safety, or procedural compliance. For instance, maintaining a minimum altitude is crucial during various phases of flight, such as during approach or in specific airspace, in order to avoid terrain or obstacles.

When an operational chart shows an underlined figure, it signifies that the pilot must not drop below that specified speed or altitude to ensure safe flying conditions and compliance with regulations. This is particularly important in different contexts such as approach speeds, where staying above a minimum ensures control and stability of the aircraft.

Understanding the importance of these minimum parameters supports a pilot in making informed and safe operational decisions.