Which of the following is NOT a reason for increased stall speed at altitude?

The choice of increased air temperature as a reason for increased stall speed at altitude is not correct because temperature does not directly affect the stall speed in a straightforward manner. When temperature increases, the air density decreases. With less dense air, the aircraft requires a higher true airspeed to generate the same amount of lift, which can lead to an increase in stall speed at altitude.

In contrast, less air density, increased altitude, and decreased airflow over the wings do contribute to a rise in stall speed. At higher altitudes, the air gets thinner, which requires a greater velocity to maintain lift. Since stall speed is based on achieving sufficient lift to counteract the weight of the aircraft, the relationship between air density and stall speed is critical. Decreased airflow over the wings, which can happen during conditions such as increased angle of attack or turbulence, further affects lift and makes stalls more likely at higher speeds.

In summary, while temperature has complex interactions with stall behavior, increased air temperature does not contribute to increased stall speed at altitude in the same direct context as the other factors do, making it the correct choice for what does not cause increased stall speed.