Son has an electric guitar to fly with but can detach the neck, if needed, and pack the body in his checked hard suitcase and carry the neck on board. We are flying business on BA IST-LHR-BOS and then AA BOS onwards for a domestic leg.

I presume there will be no issue with him just taking the neck, but wanted to see what folks here think. He could put the neck in another suitcase, but it is more delicate and I'm worried it could break. But this will be the backup plan, if neck not allowed on board. I know this is a BA thread, but if folks know what AA will do, too, that'd help.