To maintain altitude lift must equal drag.

To understand the relationship between lift and drag in maintaining altitude, it's essential to clarify the forces acting on an aircraft. Lift is the upward force that counterbalances weight, allowing the aircraft to maintain or gain altitude. Drag, on the other hand, is a resistive force that opposes the forward motion of the aircraft.

For an aircraft to maintain altitude, it primarily needs to ensure that lift is equal to weight rather than drag. When an aircraft is in a stable position and not accelerating upwards or downwards, the lift generated must equal the aircraft's weight. This means that while drag exists and must be overcome by thrust for the aircraft to maintain forward speed, it does not directly factor into the lift required to maintain altitude.

Therefore, the statement that lift must equal drag to maintain altitude is not accurate. Instead, lift must equal weight, while thrust must overcome drag, underscoring that while drag is important for forward motion, it does not dictate altitude stability directly.