AI 3318 then BA 138 at Mumbai
Patna → Mumbai → London
Timetable, Mumbai time
11:15AI 3318 from Patna at the gate
02:15BA 138 to London leaves the gate
15 h apart on the timetable, overnight
BA 138 leaves 15 h after AI 3318 arrives on the timetable: more than half a day, so not a connection we count.