True Airspeed

True Airspeed (TAS) is the actual speed of an aircraft relative to the surrounding air mass, corrected for the effects of altitude (air density) and temperature. TAS is always equal to or greater than indicated airspeed (IAS), and the difference increases with altitude.

The relationship: at sea level on a standard day, TAS ≈ IAS. At FL350, TAS is approximately 70-80% higher than IAS. A jet showing 250 KIAS at FL370 has a TAS of approximately 460 knots.

TAS is important for:

• Flight planning: Wind calculations use TAS (TAS ± wind component = ground speed)
• Navigation: Dead reckoning computations require TAS
• Performance: Engine efficiency and fuel flow rates relate to TAS at altitude
• Separation: TAS determines actual closing rates between aircraft

TAS is calculated from CAS by correcting for air density (which depends on pressure altitude and temperature). Modern aircraft compute TAS automatically from air data computer inputs. The traditional manual method uses an E6B flight computer or the approximation: TAS ≈ IAS + 2% per 1,000 feet of altitude.