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

The Air India airliner carrying 230 passengers and 12 crew members was on its way to the United Kingdom when it crashed into a building shortly after takeoff on June 12, killing all aboard, except for one survivor, and several people on the ground, according to authorities.

Relatives of the Air India crash victims are denouncing the preliminary probe as a cover-up, alleging it protects the airline, Boeing, and the Indian government. Families are rejecting compensation offers and planning legal action,