TransAsia Airways says that all 71 of its ATR pilots have begun proficiency tests after one of the airline's propeller-jets crashed into a river this past week, killing at least 36 people.

The airline said Saturday it has canceled 90 flights in the next three days to accommodate the requirement by the Civil Aeronautics Administration that its ATR pilots be retested.

Preliminary investigations indicate the pilots of Wednesday's doomed flight shut off a running engine of the ATR 72 after its other engine went idle, and aviation experts say the move could have been a mistake.

Local prosecutors have said they would be looking into the possibility of "professional error."

The Civil Aeronautics Administration said Saturday morning that seven people from the 58 on board remained missing. Fifteen people survived.