The Aviaco flight departed Zaragoza at 19:19 for a flight to Barcelona. At 20:06 the aircraft reported on a wide base leg and asked visibility data. Another aircraft (EC-AEJ) was ready for departure from Barcelona at that moment, but takeoff permission had been refused. When the Aviaco Heron reported 5 minutes away, the EC-AEJ aircraft was cleared for takeoff. Shortly thereafter both planes were flying at 150 m altitude on intersecting tracks. The Heron was forced to take a sudden avoidance manoeuvre and lost control. The plane crashed into the sea. PROBABLE CAUSE: “The fact that EC-AEJ was permitted to takeoff without the exact position of EC-ANJ being known. During avoidance action taken by EC-ANJ, loss of control occurred, and the aircraft fell into the sea.”