What effect does increasing altitude have on aircraft lift?

As altitude increases, the density of the air decreases, which is a fundamental principle in aviation. Lift is generated by the wings of an aircraft based on the airflow around them; more specifically, lift is directly related to air density, airspeed, wing area, and the coefficient of lift.

At higher altitudes, the thinner air results in fewer air molecules available for the wings to interact with. Consequently, this decreased air density negatively impacts the amount of lift generated at a given airspeed. To maintain the same amount of lift at higher altitudes, an aircraft would need to either fly faster or have a larger wing area. Therefore, the correct understanding of how increasing altitude affects lift is that it decreases lift due to the reduced air density.