Emirates President Tim Clark dashed Airbus SE’s hopes of pulling in a large order at the Dubai Air Show, saying he’s not buying more of their flagship A350-1000 until engine performance issues have been fixed.

Clark said the engine on the aircraft, built exclusively by Rolls Royce Holdings Plc, doesn’t meet the requirements in terms of time on the wing until the next maintenance cycle. Emirates would be in the market for 35 to 50 of the A350, Clark said, in what would add to an existing order book of 50 units of the widebody.

“If they can do that at a maintenance cost per hour that’s alright for us,” then Emirates would order the aircraft, Clark said in a meeting with journalists at the Dubai Air Show. “But it’s not doing that at the moment.”

Airbus had sought to follow Boeing Co.’s success, after the US company won a huge order valued at $52 billion with Emirates on Monday. The European company is the biggest supplier of super-jumbo aircraft for Emirates, though that plane is no longer in production and Emirates is currently rebuilding its fleet with new orders to factor in the switch.

Emirates wouldn’t be willing to compromise by getting a lower price, because buying an aircraft that doesn’t perform as desired makes no sense, Clark said. Reliability is particularly important for carriers in the Middle East, who run their aircraft in hot and demanding cycles, putting more strain on their planes.

Clark, calling the Rolls-Royce engine “defective,” said the powerplant only does about a quarter of the maintenance cycle that he’d typically need to see, equal to about 2,000 to 2,500. Airbus doesn’t have any other options on the aircraft as Rolls-Royce is the only engine supplier for that model.

“In the end, we cannot have a batch of aircraft letting us down all the time, it’ll destroy us,” Clark said. “We want effective, good planes that might not be as advanced, but in the end what we want is reliability.”

(Updates with additional comments from Clark throughout)