You want communications from the flight controls to the maintenance system. And you want communications from the entertainment system to the maintenance system,

You want communications from the flight controls to the maintenance system. And you want communications from the entertainment system to the maintenance system, so technicians have a single list of everything that needs fixing. It's hard to implement strict one-way communications -- usually you at least need some kind of ACK for reliable transmission. Put all those together with a vulnerability in the middle, and you have an attack.