mid-air vs midair

mid-air

noun
  • The middle of the air, as while in flight. 

midair

noun
  • The condition of being airborne. 

  • A collision between two or more aerospace vehicles in flight. 

adj
  • In the act of flight; airborne. 

How often have the words mid-air and midair occurred in a corpus of books? (source: Google Ngram Viewer )