airplane vs copilot

airplane

noun
  • A powered heavier-than-air aircraft with fixed wings. 

verb
  • To transport by aeroplane. 

  • To fly in an aeroplane. 

copilot

noun
  • A backup or assistant pilot of an aircraft. 

verb
  • To serve as relief or assistant pilot. 

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