carjack vs skyjack

carjack

verb
  • To forcibly steal (a vehicle). 

  • To steal an automobile forcibly from (someone). 

skyjack

verb
  • To steal or commandeer (hijack) an airplane, usually by threat of violence to the passengers and/or crew members. 

noun
  • Synonym of scissor lift 

How often have the words carjack and skyjack occurred in a corpus of books? (source: Google Ngram Viewer )