All four aircraft involved in the 9/11 attacks had black boxes, which include flight data recorders (FDR) and cockpit voice recorders (CVR). The black boxes from American Airlines Flight 11 and United Airlines Flight 175, which were used to attack the World Trade Center, were recovered from the wreckage. However, the recovery of the black boxes from American Airlines Flight 77 and United Airlines Flight 93, which crashed into the Pentagon and in