The BA agreement is that we can only do one B2B every 28 days. Now we have a few different types of B2B's, We have 5 day ones (when I say days I mean the amount of days it uses up on a roster) for example a 5 day JFK would mean...
LHR-JFK, Nightstop
JFK-LHR, Nightflight
Nightstop in LHR
LHR-JFK, first flight out, Nightstop
JFK-LHR, Daylight morning flight.
Then we have the 6 days which would be similar only with two standard 3day trips. Then we have a nice little 8 day at the moment where we do one nightstop followed by the DTW which has a clear day down route followed by a shuttle flight down to IAH, however this will not be lasting too much longer.
I even remember a 10 day BDA B2B where we did two 5days....it was like a little holiday where we could bring friends or family with and leave them there for the 2 nights we were back in London! Was brilliant.
Now we do get paid extra for these under our agreements however they only achieve the standard days off after any US East coast trip which is three days (4 nights) but its still a bargain. I personally love them although you do feel like you have been hit by a bus and then its reversed over you several times!!!!