“Domestic air travel is going to take several years to recover. The more problematic piece I think is international air travel,” he said during an interview at the virtual Fortune Global Forum. “I think that’s 2023, maybe early ’24, before we finally see a recovery.”

Hayes’ warning Tuesday is even more grim than his recent predictions regarding international air travel. He’s now echoing the International Air Transport Association (IATA), which this summer forecast that global passenger traffic would not return to 2019, pre-pandemic levels before 2024.

COVID-19’s global slowdown of the travel and aviation industries has hurt many large airlines and their suppliers, including Raytheon. The aerospace giant in September said that it was cutting 15,000 jobs as a result of the downturn in commercial air travel.

Hayes, who in April finalized United Technologies’ takeover of Raytheon Co., also said that he’s worrying about the pandemic’s impact on his company’s remote workforce and their long-term innovation. Working from home has boosted his employees’ productivity, but “while we’re getting work done, it’s not the same as being together and innovating,” he says.

Raytheon generally develops between 500 and 600 new patents a year—but this year, the company’s patent applications are down about 50%, Hayes said.

“We do some of the most complicated systems in the world. Whether it’s a radar, whether it’s a jet engine, whether it’s a cyber program—those things require close collaboration” from people who are physically in the same room together, Hayes said. “We’re not falling behind anywhere. But it’s an issue for us.”