United Airlines is one of historical airlines in United States.
Here is a skinpack --- Its 2nd gen Tulip + tricolor stripe and 3rd gen Battleship gray / blue liveries painted in 1974 - 2004 for Boeing 727 in Civil Aircraft Mod.
This skinpack needs "Boeing 727 Common Normal map / RoughMet Textures pack Rev3" from here. --- https://www.digitalcombatsimulator.com/en/files/3318369/
When you see strange checker blocks on the skins in DCS World, the "Boeing 727 Common Normal map / RoughMet Textures pack Rev3" is not installed / not set-up correctly.