From Command and Conquer Wiki

The Air Field was a landing strip with a flight control tower and an armory with a fuel dump, constructed by the Soviet Union. They were used to maintain aircraft that required a runway in order to land, the Yak-9 attack planes and their MiG-29 fighter jets.

The Airfield also allowed for calling in paratroopers or parabombs onboard the Badger bombers. Latter on after the war, the GDI acquired the Airfields and improves on it allowing the Airfield to support 4 planes and Orca gunships at the same time. It also helps GDI use airstrikes against enemies.