Europe's air traffic control agency says commercial aviation is expected to return to nearly normal levels throughout the region by Thursday. <br/> <br/>Eurocontrol released a statement on Wednesday saying airlines's flight schedules should be operating at nearly 100 percent levels today, one week after volcanic ash from Iceland blanketed most of the continent grounding flights and stranding millions of passengers. <br/> <br/>The agency said nearly 80 percent of European flights were in the air yesterday and that trans-Atlantic air service had returned to normal. <br/> <br/>However, the task of clearing a backlog of flights postponed or cancelled during the past week is expected to last at least several days. <br/> <br/>An industry official said the shutdown cost airlines at least 1.7 billion dollars. <br/><br/>