As the airplane slows down in flight, the angle of attack must be:

As an airplane slows down in flight, the angle of attack must be increased to maintain altitude. This is because the lift generated by the wings relies on the speed of the airflow over them and the angle of attack.

When the airplane decreases speed, the lift it produces also decreases due to the reduced airflow over the wings. To compensate for this loss of lift and maintain level flight, the pilot must increase the angle of attack. By raising the nose of the aircraft, the airflow over the wings can be altered in a way that enhances lift even at lower speeds.

It's important to note that there is a limit to how much the angle of attack can be increased before reaching the critical angle, which can lead to a stall. Pilots must be mindful of this to ensure safe flight operations.