Which airspeed is critical for the approach and landing phases of flight?

Indicated airspeed is critical for the approach and landing phases of flight because it represents the speed read directly from the aircraft's airspeed indicator. This speed is vital for pilots to know during these phases, as it provides accurate information related to the aircraft’s control and performance within the specific environmental conditions it is flying through.

During the approach and landing, knowing the indicated airspeed helps pilots maintain the appropriate speed to ensure safe and effective control of the aircraft. This is particularly important for avoiding stalls and ensuring that the aircraft generates enough lift.

While true airspeed, equivalent airspeed, and calibrated airspeed provide useful information under different circumstances, they are not as directly relevant or practical for determining operational performance in the critical phases of approach and landing. True airspeed relates more to the actual speed of the aircraft relative to the air mass and does not account for altitude effects adequately for landing scenarios. Equivalent airspeed corrects for compressibility at high speeds but is not commonly used at lower speeds typically encountered during the approach and landing. Calibrated airspeed accounts for instrument errors but again is not what pilots rely on during approach and landing since indicated airspeed has already made necessary adjustments for these factors according to standard procedures.