What effect does a tailwind during landing have on aircraft performance?

A tailwind during landing increases landing distance because it reduces the relative airflow over the wings and alters the aircraft's angle of attack. This results in the aircraft touching down at a higher ground speed compared to when landing into a headwind.

When landing with a tailwind, the aircraft will require more distance to slow down to a safe taxi speed after touchdown. Since the aircraft is moving faster relative to the ground upon touchdown, the additional kinetic energy necessitates a longer runway to decelerate.

In summary, a tailwind affects the aircraft's landing performance negatively by requiring a longer distance to land and come to a complete stop, primarily due to the higher ground speed at touchdown.