The black box of the Air India Boeing 787-8 Dreamliner that crashed immediately after take-off in Ahmedabad yesterday has been found. The hardy device which records vital data in an aircraft was found on the roof of the doctors' hostel that was hit by the aircraft. But why was it so important to find this device? And what is a black box or a DFDR? These and many more questions are answered by Vishnu Som and Shiv Aroor in the seventh episode of CTRL ALT Defence.