What is the rate of change of True airspeed?

The rate of change of True Airspeed (TAS) is influenced by altitude, as the thinner air at higher altitudes affects the aircraft's performance. Typically, TAS increases by approximately 3 knots for every 1,000 feet of altitude gained in a standard atmosphere. This relationship is due to the lower air density at greater altitudes, which allows the aircraft to maintain better performance and efficiency, thereby increasing airspeed.

By understanding this principle, it's clear that a rate of 3 knots per 1,000 feet is consistent with the standard atmospheric model used in aviation, making it the correct choice. This concept is crucial for pilots when calculating their flight performance and planning for altitude changes during flight.