The delayed arrival of aircraft engines is keeping Airbus SE from delivering some planes to customers as supply-chain problems weigh on the manufacturer’s recovery from the coronavirus crisis despite strong demand.

Twenty narrow-body jets that were fully built by the end of May were still missing engines, which will lead to late deliveries, Airbus Chief Executive Officer Guillaume Faury said in an interview.

“We have started to build planes without engines, again, as we did in 2018,” Faury said at an International Air Transport Association event in Doha. “That’s really not a good signal that shows that the tension also on the engine side is very, very strong.”

Companies across the aviation supply chain are struggling to keep up. Engine manufacturer CFM International has had supply snags and labor issues, while the maker of rival Pratt & Whitney jets, Raytheon Technologies Corp., said in April that it was facing constraints across its business. 

Faury said that aside from the engine delays, overall supply-chain challenges appear to have stabilized. Airbus plans to ramp up monthly output of its A320 series by 50%, and sees strong demand in coming years. 

“We believe for us the momentum is and will remain very positive moving forward,” said Faury. 

Airbus sales chief Christian Scherer said strong demand is “here to stay” as airlines face pressure to replace older, fuel-guzzling aircraft. He said he wished Airbus had more aircraft to sell but that given the supply-chain issues, the current pace is reasonable.