The GATE Grind

GATE 2025 AE – Question 24

Flight Mechanics & Space Dynamics · Aircraft classification and configuration, pressure altitude, equivalent, calibrated and indicated air speeds · 1 mark · Multiple choice

A general aviation airplane is flying at an altitude of 5000 m. The indicated airspeed is 250 km/h. Assume that there are no instrument errors and position errors. Neglecting compressibility effects, which one of the following options is FALSE?

  1. The true airspeed is greater than 250 km/h.
  2. The calibrated airspeed is 250 km/h.
  3. The true airspeed is 250 km/h.
  4. The equivalent airspeed is 250 km/h.

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Show answer and explanation

Correct answer: (C) The true airspeed is 250 km/h.

Explanation

With no instrument or position error, the calibrated airspeed equals the indicated airspeed, 250 km/h, and without compressibility the equivalent airspeed equals it too. The true airspeed is $V_{EAS}\sqrt{\rho_0/\rho}$, and the air at 5000 m is thinner than at sea level, so it is greater than 250 km/h. The statement that it is 250 km/h is false.