Which factor does NOT contribute to an unstable approach?

The factor that does not contribute to an unstable approach is the landing gear position. In aviation, a stable approach is characterized by specific parameters being met, including speed, descent rate, and configuration of the aircraft.

While landing gear position can play a role in the overall operation of the aircraft, it is not a primary factor in determining the stability of an approach. Typically, aircraft are required to have their landing gear down and locked at a certain altitude, but the act of having the landing gear down itself does not directly induce instability in the approach if all other parameters are within acceptable limits.

In contrast, aircraft configuration, ATC instructions, and descent planning are integral elements that can significantly impact the stability of an approach. The configuration of the aircraft, which includes flaps and speed settings, directly influences how well the aircraft can maintain the desired trajectory. ATC instructions can lead to changes in flight path or altitude that may affect approach stability. Descent planning involves calculations and strategies that help ensure a smooth transition to landing, which is vital for maintaining a stable approach.