United Airlines has abruptly announced that it is changing its sole San Francisco to Shanghai service to first stop in Seoul. The carrier’s nonstop flights to China had restarted in October on the route with four weekly flights.

“Due to changes in operating conditions, we adjusted service between San Francisco and Shanghai to now include a stop in Seoul, South Korea, for a crew change as we did earlier this year,” United said in a statement.

According to reports from CNBC, lengthy waits for testing on arrival, concerns with government-designated hotels, and restrictions on movement are just some of the challenges airline crews face on flights to China.

Flights by US carriers to China resumed following a reciprocal agreement reached in July between Chinese and US aviation authorities which allowed US airlines to return to some of their pre-COVID-19 Chinese routes.

By scheduling a stop in the South Korean capital to swap crew, United says it is able to circumvent on-arrival testing and overnight stays in China for pilots and flight attendants.

Delta, which restarted nonstop flights to Shanghai from Detroit and Seattle this week, has not yet announced or made any changes. Meanwhile, American Airlines resumed China service with flights between Dallas-Fort Worth International Airport and Shanghai, also with a stop in Seoul.

united.com, delta.com, aa.com