The European Aviation Safety Agency ordered operators of Airbus SE A350 airliners to revise fuel-system software to reduce the risk of overheating that could lead to a fire. A flaw in the hydraulic-fluid cooling system, located in the fuel tanks, may cause the temperature of the liquid to rise quickly, the EASA said in an emergency airworthiness directive that took effect Thursday. That could lead to overheated fluid igniting the fuel-air mix in the tank if its fire-extinguishing system isn’t working. Airbus has delivered 100 of the A350, its latest twin-aisle jet, and booked total orders of 848, making the model one of the company’s most important aircraft. While customers have praised its fuel efficiency and economics, deliveries have been delayed as supplier Zodiac Aerospace hasn’t been able to provide some interiors on time. The bestselling A350-900 variant has a list price of $311.2 million, making it Airbus’s third-most expensive model. Reuters reported on the EASA’s announcement earlier Thursday. The A350’s biggest customers include Qatar Airways Ltd., Singapore Airlines Ltd. and Cathay Pacific Airways Ltd. Airbus has informed the model’s operators of the problem, asking them to monitor the system, a spokeswoman at the Toulouse, France-based planemaker said. The manufacturer is working on a software fix that should be available “in coming weeks,” she said.