Ahmedabad plane crash: What is Blackbox; what makes it crucial evidence

An Air India flight AI-171, a Boeing 787-8 Dreamliner, crashed after taking off from Ahmedabad airport. The flight was headed to London Gatwick. All 242 people on board are feared dead. Rescue operations are underway. Investigators are prioritizing the recovery of the black box. The black box holds vital clues to determine the cause of the crash.