Performance charts must be read using indicated airspeed instead of true airspeed because:

Performance charts must be read using indicated airspeed instead of true airspeed because:

• A. IAS equals TAS at sea level
• B. Performance charts reflect air density changes via IAS; TAS would misrepresent density effects
• C. TAS is more accurate
• D. IAS is measured by a different instrument

Answer: (B)

The main idea is that aircraft performance is governed by dynamic pressure, which depends on air density and the square of speed. Indicated airspeed (IAS) directly tracks dynamic pressure because the pitot-static system measures impact pressure, and IAS is the calibrated readout that reflects that pressure under standard density conditions. Performance charts are built to show how lift, drag, engine airflow, and overall performance respond to a given dynamic pressure, not to a specific true airspeed. As you climb and air becomes less dense, the same true airspeed does not produce the same dynamic pressure as at sea level. If you used true airspeed on the charts, you’d be mixing in the density changes improperly, and the charts would misrepresent how the airplane actually performs in thinner air. Using IAS keeps the density effects tied to the chart readings, giving consistent, accurate performance predictions across different altitudes.

The main idea is that aircraft performance is governed by dynamic pressure, which depends on air density and the square of speed. Indicated airspeed (IAS) directly tracks dynamic pressure because the pitot-static system measures impact pressure, and IAS is the calibrated readout that reflects that pressure under standard density conditions. Performance charts are built to show how lift, drag, engine airflow, and overall performance respond to a given dynamic pressure, not to a specific true airspeed.

As you climb and air becomes less dense, the same true airspeed does not produce the same dynamic pressure as at sea level. If you used true airspeed on the charts, you’d be mixing in the density changes improperly, and the charts would misrepresent how the airplane actually performs in thinner air. Using IAS keeps the density effects tied to the chart readings, giving consistent, accurate performance predictions across different altitudes.