AA 1659 then UA 3998 at Charlotte
Buffalo → Charlotte → Washington
Timetable, Charlotte time
07:45AA 1659 from Buffalo at the gate
19:55UA 3998 to Washington leaves the gate
12 h 10 apart on the timetable
UA 3998 leaves 12 h 10 after AA 1659 arrives on the timetable: more than half a day, so not a connection we count.