cockpit voice recorder vs flight recorder

cockpit voice recorder

noun
  • A flight recorder which records the audio environment in the flight deck of an aircraft. 

flight recorder

noun
  • A device which records data that would be of use in investigating the cause of an aircraft accident; usually in pairs, consisting of a flight data recorder and a cockpit voice recorder. 

How often have the words cockpit voice recorder and flight recorder occurred in a corpus of books? (source: Google Ngram Viewer )