During the ground assault on the Rebel base on Hoth why didn't the Imperials provide air support to their forces? During many battles here on Earth, military units regulary have access to air support, even more so when they control the air directly over the ground battle.
Given that there were several Star Destroyers in orbit around Hoth, it would seem logical that a handful of TIE fighters could have been assigned to the ground assault and would have been effective in protecting the AT-AT's from the Rebel air speeders. So, why no air cover for the AT-AT's?