German airline giant Lufthansa said Wednesday it was forced to cancel or delay flights across its airlines after construction work in Frankfurt caused a major IT outage. Frankfurt airport, Lufthansa’s main hub, said it had stopped most planes from landing to avoid overcrowding as thousands of passengers were unable to board flights. Lufthansa said the IT systems failure had been caused by construction work in the Frankfurt region that had damaged broadband fiber-optic cables. “Flight operations are expected to stabilise in the early evening,” it added. Lufthansa is Europe’s biggest airline group. It also owns Eurowings, Swiss, Brussels and Austrian Airlines. The group did not immediately specify how many flights or passengers were impacted globally but Frankfurt and Munich airports appeared among those most affected. Deutsche Telekom said four of its cables had been “damaged” during construction work ordered by state-owned rail operator Deutsche Bahn in Frankfurt a day earlier. “We are in the process of repairing these fiber optic cables, two are already fixed,” a spokesman told AFP. German newspaper Bild spoke of “chaos” at Frankfurt and Munich airport because of problems with Lufthansa’s check-in and boarding systems. Lufthansa said it regretted the inconvenience caused and asked travellers to check their flight status online before travelling to Frankfurt airport. It also urged passengers on domestic flights to book train journeys instead. The turmoil comes as Germany is bracing for a full-day strike at seven airports on Friday, including at Munich and Frankfurt. The stoppage has been called by the Verdi trade union, which is currently leading negotiations for better pay for public sector workers, airport ground crew and aviation security staff. The one-day walkout is expected to lead to flight disruptions for thousands of passengers.