Investigators are combing the wreckage of Air India flight AI171 to determine what caused the Boeing 787 Dreamliner to crash Thursday, killing all but one of the 242 people aboard and resulting in the deadliest aviation accident in more than a decade.

On Friday morning, one of the two so-called black boxes, which contain critical evidence of a plane’s final minutes, was located, the India Aviation Ministry said. The ministry said it found the digital flight data recorder on the rooftop of the plane.

The accident site remains a scene of total devastation, with burnt debris and scattered aircraft parts still smoldering. The BJ Medical Hostel, where medical students were dining at the time of the accident, has been severely damaged, with four tower blocks half-burnt and blackened. Firefighters continue to spray water on the site, while police and officials work to clear the wreckage.