Scores of flights to and from Germany's biggest airport Frankfurt were scrapped Monday because of a software problem affecting the national air traffic control service.
By noon, 66 flights had been cancelled, said the air navigation service provider DFS, which cited an IT glitch in its control centre in Langen, Hesse state.
The agency has assured the public that "the safety of air traffic is not impaired".
The DFS first announced last Wednesday that a "software malfunction" at Langen was affecting the Frankfurt, Cologne Bonn, Stuttgart and Duesseldorf airports.
The glitch had impacted the system that transmits flight data such as aircraft type, route and expected time overhead to air traffic controllers.
The DFS said last week it had reduced air traffic volume within Langen's area of responsibility, which stretches to Lake Constance in the south, Kassel city to the north, the French border to the west and Thuringia state to the east.
The state-owned DFS has 5,400 employees, including around 2,000 air traffic controllers who guide up to 10,000 flights a day in German airspace, totalling more than three million movements a year.