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

Authorities in India have released the preliminary results of their investigation into the the Boeing 787-8 Dreamliner crash in June that killed 229 of the 230 passengers aboard and all 12 crew members.

The two engines on the Air India flight shut down within one second of each other before the Boeing 787 Dreamliner crashed last month in Ahmedabad, India, killing at least 260 people, according to a preliminary report released Friday.