What do you think would happen if someone planted cryptolocker-inspired malware on a planes avionics suite and denies it's use to the flight crew? Especially one of the newer models which are exclusively fly-by-wire?
Cryptolocker attacks have very little to do ideologically with encryption; it's a side show to the main event, the fact that networks are vulnerable to infiltration. Those attacks could happen with or without encryption in the malware, but could be reduced in frequency and severity by using strong systems with strong encryption on the victims' side.
The airplane bit is where the scenario goes completely off the rails wrt encryption's involvement, but again, using encryption and strong security on the airplane's systems would reduce or eliminate the risk.
