The thrust output of a turbojet-powered aircraft is greatest when performing which action?

• A. During takeoff with light load
• B. On the brakes on the runway at full thrust
• C. In steady cruise
• D. During engine idle on the ground

Answer: (B)

Thrust from a turbojet is determined by how much air the engine can ingest and how fast it exits the nozzle, which is controlled mainly by the throttle setting and engine speed. When the throttle is shoved to full power, the engine draws in the maximum air and accelerates it through the turbine, producing the highest possible thrust. Being on the brakes while applying full thrust doesn’t change the engine’s capability—it simply prevents the airplane from moving, so the engine can deliver its peak thrust without any acceleration load or airspeed to contend with. In steady cruise, the engine runs at a lower power setting, so thrust is less. Idle on the ground yields even less thrust.