Abstract: An aircraft-conversion method of converting a passenger aircraft to a cargo aircraft, includes selecting a passenger aircraft, and converting the aircraft to a cargo aircraft by changing a door of the aircraft to accommodate loading and unloading of cargo. The selecting step may involve an all-passenger aircraft, and the converting step may include removing all seats from the aircraft. A system for converting a passenger aircraft with a passenger door for passenger entry and exit to a cargo aircraft includes aircraft-door conversion structure constructed to replace the passenger door with a cargo door that allows loading and unloading of cargo on the aircraft via the cargo door. A converted cargo aircraft includes an aircraft body, and aircraft-door conversion structure constructed to replace the passenger door with a cargo door that allows loading and unloading of cargo on the aircraft via the cargo door.