Certified Flight Instructor - Flight Instructor Airplane Practice Exam

What happens to true airspeed as density altitude increases while maintaining constant indicated airspeed?

1. True airspeed increases; groundspeed decreases

2. True airspeed decreases; groundspeed decreases

3. True airspeed increases; groundspeed increases

4. True airspeed remains the same

The correct answer is: True airspeed increases; groundspeed increases

As density altitude increases while maintaining a constant indicated airspeed, true airspeed actually increases. This occurs because indicated airspeed (IAS) is a measure of dynamic pressure, which remains constant at a specific indicated speed regardless of altitude or air density. However, as density altitude rises, the air becomes less dense. In this situation, to maintain the same IAS, the aircraft must produce more lift as it ascends to higher altitudes. The decrease in air density at higher altitudes results in a lighter mass of air for the wings to act upon, thus requiring the aircraft to fly at a higher true airspeed (TAS) to achieve the same lift as at lower altitudes. Additionally, since true airspeed is the speed of the aircraft relative to the air around it, and given that groundspeed is the speed of the aircraft over the ground, true airspeed will increase while groundspeed may or may not change depending on wind conditions. If there are no adverse winds (i.e., a tailwind), both true airspeed and groundspeed would increase, though the relationship is influenced by wind. In simplest terms, if we isolate the factors, as long as the IAS is held constant, the true airspeed will increase with an increase