Horter was an Air Force serviceman who was an air-base flight coordinator during Day 4.
Mitch Anderson, a mercenary (and former Air Force pilot) hired by the terrorist Habib Marwan, sought to infiltrate a USAF base and hijack a F-117 stealth fighter. He disguised himself as John Hansen, a pilot whom he killed, and slew the mechanic Lenkov to fake the necessary flight paperwork. To finally hijack the plane, Anderson dressed in Lenkov's clothes in order to deceive Horter, who was aware of a serious problem with the aircraft. Anderson disarmingly dismissed the issue, and used the false papers to trick the officer. Horter, satisfied, made the call which cleared the plane for take off. Anderson eventually attacked Air Force One.
Background information and notes
Despite he identified himself as Horter, the name on his overalls tag is "Kronish", naming after producer Stephen Kronish.