What are indications of an impending stall?

An impending stall is characterized by specific aerodynamic cues, primarily related to the behavior of the aircraft's control surfaces and its overall flight attitude. The correct choice highlights several critical indicators:

Loss of elevator effectiveness occurs as the airplane approaches a stall because the airflow over the wings and control surfaces begins to separate, reducing their effectiveness. This can lead to a situation where the pilot has to exert more force on the control stick to maintain the desired pitch attitude, which is described by encountering increased control stick forces. Additionally, the uncommanded nose-high attitude can manifest as the aircraft approaches the critical angle of attack, signaling that the plane is at risk of losing lift.

Recognizing these signs is crucial for pilots in order to take corrective action, such as lowering the nose or reducing the angle of attack, to recover from a potential stall before it occurs. The other options do not accurately represent the sensations or conditions most clearly associated with an impending stall, thereby making the selected answer the most relevant.