A freak bout of electrical storms over Germany is to blame for the worst monthly punctuality record at Deutsche Lufthansa AG in at least two years, according to the company.

The country suffered more lightning strikes in the first five months than in the whole of 2017, with planes hit by an average of three bolts a week, according to Thorsten Dirks, the Lufthansa board member responsible for the group’s Eurowings division. The low-cost operator in particular has struggled to cope as it absorbs planes and businesses acquired by its parent.

Aircraft have to undergo safety checks following lightning hits, taking them out of action for up to 16 hours. Airports including Munich, Germany’s second-busiest, have also suspended operations during the bad weather.

“These are turbulent times,” Dirks said in a briefing in Frankfurt. Across Lufthansa as a whole in May, close to 35 percent of flights failed to arrive within 15 minutes of the scheduled time, the worst monthly performance since at least 2016, according to data provided by flight-scheduling firm OAG. Some 3.3 percent of flights were canceled, the highest proportion this year.

The situation has been exacerbated by a series of strikes by air traffic controllers in France and Italy, Dirks said. The walkouts have hurt punctuality at several carriers, especially for flights between northern Europe and the Mediterranean.

Eurowings has been especially stretched as it suffers “growing pains” from taking on more than 100 aircraft over the past three years after Lufthansa acquired full control of Brussels airlines and bought about half of the fleet of defunct rival Air Berlin Plc.

Lufthansa is expanding Eurowings as it battles to keep discount giants Ryanair Holdings Plc and EasyJet Plc at bay in its main markets. Following the collapse of Air Berlin and Britain’s Monarch Airlines Ltd. and with Italy’s Alitalia SpA in administration, further consolidation is likely and could fuel growth, Dirks said.