Originally Posted by
EvilDoctorK
Without knowing the detail I always thought it was an East/Westbound thing .. it's not just BA .. but on Transatlantic anyway most airlines seem to follow the convention that Eastbound flight are even numbered and Westbound odd numbered
I did think it might be that, but Cape Town is (slightly) east of London, and its the same with DXB (BA 105/104, 107/106, 109/108) and DEL (BA 143/142), as well as the rest of the Indian routes, except MAA which is 35/36. Also when Concorde flew (and when the LCY-JFK all J flight flew) BA 1 and 3 were outbound, and 2 and 4 were inbound. So at the very least it's inconsistent.
And even so, all of BA's long haul outbound flights are odd numbers, East and west, just that for higher numbers the return is that -1, whereas for the lower numbered routes the return is +1