BA 391 then BA 486 at Heathrow
Brussels → London → Barcelona
Timetable, London time
14:20BA 391 from Brussels at the gate
15:15BA 486 to Barcelona leaves the gate
55 min apart on the timetable
The last days
BA 391 and BA 486 weren’t both flown 15 min to 12 h apart in the last 21 days.
Statistics from past flights, not live flight information. Always check times and your connection with your airline, and don’t base travel or booking decisions on these numbers.