From Longman Dictionary of Contemporary Englishfly the coopfly the coopAmerican English informalESCAPE to leave or escape All my children have flown the coop now. → fly
Examples from the Corpus
fly the coop• The Tomahawk cruise missile, born in 1972 and built here ever since, has flown the coop.• Then Deutschlandsender made their announcement yesterday that Hess had flown the coop and I think that clinched it for them.• Plus it discourages funds that have already flown the coop from changing course and heading home again.• All my children have flown the coop now. 