| True Airspeed "Squared" Rule
A quick way to calculate TAS from IAS:
Sea Level TAS = IAS
5,000ft TAS = IAS + 9% (3 squared).
10,000ft TAS = IAS + 16% (4 squared).
15,000ft TAS = IAS + 25% (5 squared).
20,000ft TAS = IAS + 36% (6 squared).
25,000ft TAS = IAS + 49% (7 squared).
30,000ft TAS = IAS + 64% (8 squared).
35,000ft TAS = IAS + 81% (9 squared).
40,000ft TAS = IAS + 100% (10 squared).
e.g. 250 kts IAS at 10,000 ft = 290kts IAS; at 25,000ft = 373kts IAS; at 40,000ft = 500kts IAS. |