The concept of "killswitch" came around in early 80s when primitive microprocessor were able to control functions within a complex system.. Large non military systems such as digital telephone exchanges were being intoregated remotely by the manufacturer with out the customers being aware..today's passenger jet engines talk to the manufacturer without pilots knowing..all for good reason of safety and maintenance
It is a software feature that allows the manufacturer to turn a system on or off or makes it to do things a customer does not have any clue of.
Any large military system such as Aircraft, air defence..etc have these features embedded into their software and the possibilities of what a manufacturer can do with them is endless..they will never admit to having this capability and will only be used in extreme cases like defection let's say a pilot to another country and recorded as malfunction or pilot error.