The failure of a take-off warning system may be to blame for the Spanair crash that killed 154 people at Madrid’s Barajas airport in August, according to the preliminary findings of an accident investigation released on Friday.

Spain’s Civil Aviation Accident Investigation Commission (CIAIAC) suggested in an initial 12-page report that the pilots tried to take off with the wings’ flaps, which help give lift, at “0 degrees”. This compares with the “11 degrees of deflection” noted on an earlier, aborted takeoff, say investigators. It says the pilots were unaware of the error due to the failure of an alarm normally triggered when an aircraft is not correctly configured for takeoff.