A wirecutter would presumably cause an issue which would manifest itself prior to takeoff.
Either that, or you must make your way into the bay while in flight with said wirecutters.
Now, a dongle quietly manipulating enough variables to make the plane uncontrollable in flight, on the other hand... (No idea if that is even possible given access to this bus, but I will read this paper with some interest tomorrow (As I fly AMS-EWR... :)
Manipulating actual flight controls is probably hard.
Manipulating sensors is probably comparably easy, and, if you can adjust the AOA sensors to make the plane think its in level flight while spoofing altitude data, you can probably manipulate the pilots (auto or not) into a CFIT.
It's happened on other flights where pilots became confused by conflicting information (AF447 and many others) so giving them consistently wrong data is going to cause a consistently bad output.
Anyway though I deeply agree that once you have physical access all bets are off. Sure, you can put a bug in which causes a complicated aircraft failure but you could also just put a time-delayed container of thermite or tannerite in the right place.
I'd be much more worried about a software update causing a major issue, either intentionally or even more likely and more worrying, accidentally ALA 737Max.
>Manipulating actual flight controls is probably hard.
Why? The flight sticks have an ADC, just control current/resistance there to get the desired digital values. Of course assuming fly by wire an symmetrical input on both sticks.
Probably far easier than manipulating the digital data downstream, which is subject to lots of checks.
There was a somewhat recent event of someone proving he could control an airplane from the passenger compartment. They went into the logs and he made minor course adjustments.
They seized his equipment but it didn’t say he spent any time in jail.
Either that, or you must make your way into the bay while in flight with said wirecutters.
Now, a dongle quietly manipulating enough variables to make the plane uncontrollable in flight, on the other hand... (No idea if that is even possible given access to this bus, but I will read this paper with some interest tomorrow (As I fly AMS-EWR... :)