Which condition yields the greatest thrust output for a turbojet-powered aircraft?

• A. Takeoff with light fuel load
• B. Brakes applied with full throttle
• C. Cruise at altitude
• D. Idle on the ground

Answer: (B)

The main idea is that turbojet thrust is driven by engine speed and fuel flow, which you control with the throttle. When the throttle is at maximum, the engine is producing the most thrust it can, regardless of the aircraft’s weight or speed. Brakes on the airplane don’t change the engine’s ability to produce thrust—they just prevent the aircraft from moving. So, with the throttle wide open, the engine delivers its greatest thrust output, even though the brakes keep the airplane stationary.

The other situations either limit engine power (idle, or operating at cruise where the engine isn’t at full throttle) or don’t maximize the engine’s power available to produce thrust.