Plain English Meaning

The speed reading shown on the airspeed gauge in the cockpit. In a thunderstorm, that reading can jump around or become wrong, so pilots are told to fly a steady power and pitch instead of trying to hold a specific speed.

Full Definition

The airspeed value displayed on the airspeed indicator, derived from the difference between ram (pitot) pressure and static pressure. In a thunderstorm encounter, airspeed indications can become erratic or unreliable due to turbulence, rapidly changing pressures, and possible icing or water ingestion in the , so is advised to a and a rather than the .