An increase in altitude and temperature typically causes the indicated airspeed to:

An increase in altitude and temperature typically causes the indicated airspeed to decrease significantly due to the relationship between air density and indicated airspeed. As altitude increases, the air becomes less dense, resulting in fewer air molecules for the aircraft to interact with. This reduction in air density affects the lift generated by the wings and the drag experienced, which in turn influences the indicated airspeed—this is the speed that is displayed on the aircraft's airspeed indicator.

Indicated airspeed is calibrated for sea level conditions and relies on the density of the air to provide an accurate measurement. As you ascend to higher altitudes where temperature may also increase, the density continues to decrease, leading to a lower indicated airspeed reading. Although true airspeed— the actual speed of the aircraft through the air—may remain constant or even increase, the indicated airspeed decreases due to the lower pressure and density, which affects the real-time readings on the airspeed indicator. This relationship is essential for pilots to understand for safe operation, particularly in varying conditions of altitude and temperature.