Originally Posted by
smilee
Is back-to-back legal if you use two different airlines.
It is never "illegal" but it is a violation of the CoC. They can cancel your tickets or terminate your FF program membership but you're not going to jail.
That being said, using two different airlines is quite fine since you are following the CoC of each airline for the ticket you have with them. A codeshare is a rather gray area (AS code on AA metal and then AA code on AA metal) but I wouldn't risk that one.