An NTSB audio recording indicates that minutes before a collision between a helicopter and airplane that killed all nine occupants over the Hudson River last month, the pilot of the airplane appears to have misheard the radio frequency for the air traffic control tower he was instructed to communicate with. An air traffic controller instructed the pilot to tune in to the Newark Liberty International Airport frequency, 127.85, but the pilot read back 127.87, and the controller, who was alone in the tower and was having a personal phone call, missed the incorrect read-back.