During a turn, why must back elevator pressure be increased to maintain altitude?

During a turn, increasing back elevator pressure is necessary to maintain altitude primarily because of the loss of the vertical component of lift. When an aircraft turns, the lift vector tilts along with the aircraft. This results in a portion of the lift acting horizontally to provide the necessary centripetal force for the turn, effectively reducing the amount of lift that acts vertically.

To maintain altitude, the pilot must compensate for this reduction in the vertical component of lift by increasing back elevator pressure. This action raises the aircraft's nose, increasing the angle of attack and, consequently, the lift generated by the wings. Thus, it ensures that the aircraft continues to climb or maintain its altitude during the turn.

In contrast, while increases in drag and adverse yaw are relevant considerations in a turn, they do not directly relate to the necessity of adjusting elevator pressure to maintain altitude. Drag might require more power to maintain speed, and adverse yaw concerns the aircraft's directional control, but they do not specifically address the change in lift dynamics caused by the bank angle.