What happens during a porpoising landing error?

During a porpoising landing error, the aircraft exhibits a bouncing motion that alternates between the nose gear and the main gear upon touchdown. This phenomenon typically occurs when the aircraft's landing approach is not stabilized, leading to an uneven distribution of weight and forces during landing.

As the aircraft touches down, if the main gear contacts the runway first and the angle of attack is too high, the nose will pitch down, resulting in the nose gear hitting the runway. This action can then cause the main gear to lift off again, followed by a subsequent bounce back to the main gear, creating a cycle of bouncing between the two sets of wheels. The situation can escalate if not corrected properly, potentially damaging the aircraft or causing a loss of control.

The other options refer to different errors or conditions during landing: touching down at a lower speed indicates a different landing issue, maintaining a steady descent means the aircraft is landing correctly, and entering a stall before touchdown is a separate critical problem altogether. Understanding the mechanics of porpoising is crucial for pilots to ensure safe and effective landings.