When penetrating a horizontal wind shear, which parameter changes first?

When an aircraft penetrates a horizontal wind shear, the first parameter to change is the indicated airspeed. In wind shear conditions, particularly when there is a change in the wind speed or direction at a different altitude compared to the aircraft's current state, the aircraft experiences a shift in the relative wind. This change affects how the airspeed is perceived with respect to the aircraft's airframe.

As the aircraft encounters varying wind speeds, its indicated airspeed can fluctuate before other parameters like ground speed, pitch angle, or vertical speed react to these changes. The indicated airspeed is directly influenced by the dynamic pressure felt by the aircraft at its current attitude, and any alteration in the wind can immediately modify the reading.

Changes in ground speed will occur subsequently, as these derive from the combined factor of the indicated airspeed and wind component acting on the aircraft. Similarly, pitch angle and vertical speed adjustments follow after the flight crew or automated systems respond to the initial fluctuations in airspeed. Therefore, indicated airspeed is the first notable effect when entering a horizontal wind shear environment.