How do you calculate true airspeed (TAS)?

To calculate true airspeed (TAS), the correct method involves adjusting calibrated airspeed (CAS) for changes in altitude, which can effectively be done using the method described in option B. As an aircraft climbs, the air density decreases, and the effect on indicated airspeed means that a correction must be applied to obtain true airspeed.

Using a formula where TAS is equal to CAS plus 2% of CAS for every 1,000 feet of altitude accurately reflects this adjustment: for every 1,000 feet climbed, the CAS is effectively reduced due to lower air density; thus, adding 2% of the CAS accounts for this decrease and converts it into TAS. This method provides an approximation that is practical for pilots in varying altitudes.

The other calculations suggested would not yield the correct true airspeed value. For instance, using a fixed percentage increase like 10% for every 1,000 feet is not aligned with the actual decrease in air density and airflow characteristics with altitude. Similarly, using wind speed or ground speed for calculating TAS doesn't accurately reflect the relationship between indicated and true airspeeds, as these factors do not directly adjust for altitude-related changes in air pressure and density.