As altitude increases, how is True Airspeed estimated from Indicated Airspeed?

As altitude increases, the relationship between Indicated Airspeed (IAS) and True Airspeed (TAS) changes due to the decrease in air density. True Airspeed is the actual speed of an aircraft relative to the surrounding air, while Indicated Airspeed is what is shown on the airspeed indicator, which is affected by air density.

The correct method to estimate True Airspeed from Indicated Airspeed involves adding a percentage increase based on the altitude increase. Specifically, it is a widely accepted rule in aviation that you should add 2% of the Indicated Airspeed for every 1,000 feet of altitude gain. This adjustment accounts for the decrease in air density with altitude, which affects the performance and airspeed readings of the aircraft.

This accumulation of 2% for every thousand feet leads to a precise understanding of how aircraft performance changes as they ascend, crucial for flight planning and navigation safety. Thus, the correct understanding of how to transition from Indicated to True Airspeed at different altitudes is foundational for pilots flying under Instrument Flight Rules.