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> the F.B.I. issued a bulletin to airlines to be on the lookout for passengers showing signs they may be trying to hack into an airplane's Wi-Fi or inflight entertainment system

What a joke! An well-organized effort to break into passenger jet flight control systems doesn't need to possess any outwards visible behavior cues.

All any break-in needs is a person carrying a malicious transponder to interface with, and relay command and control transmissions.

They can just sit there, while someone else remotely transmits commands, which are then tunneled through the relay device. At that point, the limitations of the attack vector would be reduced to line-of-sight, and the remote transmitter's signal strength.

So then, what you have is a person carrying what appears to be a cell phone, but the guts have been replaced with a black box transponder. Some one from miles away could then broadcast signals to the transponder, which then delivers payloads, and returns the details of the avionics systems state.