My son is on the bigger side, when he was 4 months he barely fit into the bassinet on an LX 77W, and he wouldn't go to sleep there. Also it was very high up compared to the seats, so he couldn't see us and got upset.
We use an ergobaby to carry him around and he slept in that. Not sure when we are next flying with him but he definitely won't fit in a bassinet any more. Also we are going to have to try and book mostly daytime flights.