In steady-level flight, which pair of forces balance to maintain altitude?

• A. Lift equals weight; Thrust equals drag
• B. Lift equals thrust
• C. Weight equals drag
• D. Lift equals drag

Answer: (A)

In steady, level flight the aircraft isn’t accelerating up or down, so vertical forces must balance. Lift must equal weight so there is no net vertical force to change altitude. At the same time, to keep the airplane flying at a constant speed, the propulsion system must overcome the air’s resistance, so thrust must balance drag. Together, lift equals weight and thrust equals drag keep the airplane at a constant altitude with steady flight.

Lift equals thrust or weight equals drag or lift equals drag don’t produce the necessary balance in both axes, so they wouldn’t maintain steady, level flight.