An Air India Ahmedabad-London flight took off at 1.39 pm. Under a minute later, it plummeted from an altitude of 625 feet and crashed into a doctors' hostel, with several casualties feared both inside the aircraft and in the building it damaged. The plane erupted into flames, sending thick smoke into the sky. As firefighting and rescue teams work on the spot of the crash, a deeper look into the reason behind it will likely be clear from a small box sitting in a corner of the aircraft - the black box.