What primarily causes a decrease in aircraft performance when ice forms on wings?

The formation of ice on aircraft wings primarily leads to a decrease in performance due to an increase in drag and weight. When ice accumulates on the wings, it disrupts the smooth airflow over the surface, which is essential for maintaining lift and minimizing drag. As the ice alters the wing's shape, it can create additional turbulence, leading to increased drag, which in turn requires more power to maintain speed and altitude. Furthermore, the added weight from the ice accumulation can negatively impact the overall aircraft performance as it affects the lift-to-weight ratio and increases the stall speed.

The other choices do not accurately reflect the main issues related to ice formation on wings. For instance, ice does not improve aerodynamics; if anything, it significantly impairs efficiency and control. Decrease in altitude readings is not a primary factor; while ice can affect certain instruments, it is not the main consequence of ice on wings. "None of the above" also does not capture the significant impact of drag and weight due to ice formation, which is a critical aspect of the aircraft's performance during flight conditions.