An official report on the world’s deadliest aviation accident in a decade has answered one key question – but raised others.

Air India flight AI171 had barely left the runway last month when it lost momentum and crashed in a densely populated area of India’s western city of Ahmedabad, killing all but one of the 242 people on board and 19 others on the ground.

Now, a preliminary report by India’s Aircraft Accident Investigation Bureau (AAIB) has revealed that fuel supply to both engines was cut in the crucial minutes as the aircraft was ascending.

The plane’s “black box,” its flight data recorder, showed that the aircraft had reached an airspeed of 180 knots when both engines’ fuel switches were “transitioned from RUN to CUTOFF position one,” the report says. The switches were flipped within a second of each other, halting the flow of fuel.

On an audio recording from the black box, mentioned in the report, one of the pilots is heard asking the other why he flipped the switches. The other pilot responds that he did not do so. The report does not specify who was the pilot and who was the co-pilot in the dialogue.