holding pattern vs obstruction

holding pattern

noun
  • Any failure to advance; useless or unproductive activity. 

  • A path taken by an aircraft waiting to land. 

obstruction

noun
  • Something which obstructs or impedes, either intentionally or unintentionally 

  • The act of obstructing, or state of being obstructed. 

  • The condition of having the natural powers obstructed in their usual course; the arrest of the vital functions; death. 

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