Private Pilot License (PPL) Aerodynamics Practice Exam

As altitude increases, what happens to the indicated airspeed at which a given airplane stalls?

1. It decreases

2. It increases

3. It remains the same regardless of altitude

4. It varies with atmospheric pressure

The correct answer is: It remains the same regardless of altitude

The indicated airspeed at which an airplane stalls does indeed remain the same regardless of altitude, primarily due to the nature of indicated airspeed (IAS) versus true airspeed (TAS). Indicated airspeed is a reading that comes directly from the pitot-static system and is based on the dynamic pressure of the air, which is influenced by both the density of the air and the speed of the aircraft. As altitude increases, air density decreases, which means that for a given weight and configuration, the true airspeed at which a stall occurs will increase due to the lower density. However, the indicated airspeed does not change with altitude because it is a measurement relative to the local air pressure and temperature at that altitude. Therefore, even though the true stall speed increases with altitude due to changing air density, the indicated airspeed—essential for pilots to understand and use as a reference for stall warnings—does not change. This understanding is crucial for pilots to maintain adequate control and to react appropriately when nearing stall conditions at varying altitudes.