What can indicate that the flaps have lowered?

When flaps are lowered on an aircraft, they alter the aerodynamic characteristics of the wing, primarily increasing lift and drag. This change in lift tends to cause the aircraft's nose to pitch upwards slightly, which is often noticeable to the pilot. This pitching up can be attributed to the change in airflow and lift distribution, allowing for safer maneuvers during flight phases such as approach and landing.

A sudden drop in altitude generally signifies other issues, such as a loss of lift or a steep descent rather than the correct functioning of flaps. Visual confirmation through indicators is important but is a method of verification rather than an immediate indicator of flap position. Although a change in engine sound could occur during flap deployment, it is not a reliable or direct indication of flap position. The pitching up of the nose is the most immediate and perceptible reaction associated with lowering the flaps, making it a strong indicator of their deployment.