If your transatlantic flight and the BMI flight are together you will be allowed two pieces up to 70 lb, the area of conflict may be your carry-on. Generally speaking when twoi different baggage concepts clash, two pieces wins out over weight. If your ticket is seperate, the limits should be something like 23kg in Y and 30kg in C, with BMI expect then to give you grace of about 25% over that. Also If you are *Gold you get an extra piece.