An Ethiopian Airlines' Boeing 787 Dreamliner prepares to take off from Addis Ababa airport in Ethiopia, Saturday, April 27, 2013. A Boeing 787 operated by Ethiopian Airlines flew from Ethiopia to Kenya's capital Nairobi on Saturday, the first commercial flight since air safety authorities grounded the Dreamliners after incidents with smoldering batteries on two different planes in January.

An Ethiopian Airlines' Boeing 787 Dreamliner prepares to take off from Addis Ababa airport in Ethiopia, Saturday, April 27, 2013. A Boeing 787 operated by Ethiopian Airlines flew from Ethiopia to Kenya's capital Nairobi on Saturday, the first commercial flight since air safety authorities grounded the Dreamliners after incidents with smoldering batteries on two different planes in January. (© AP Photo/Elias Asmare)

CHICAGO (AP) —United Airlines expects to start flying its Boeing 787s again on May 20.

The 787s had been grounded because of concerns about smoldering batteries, but they have been returning to the skies. Ethiopian Airlines was the first to fly a 787 again, on April 27.

The first United flight will be from Houston to Chicago. A spokeswoman for United Continental Holdings Inc. says the first flights will be around the U.S. She says international flights will begin when the airline uses the 787 for new flights from Denver to Tokyo starting June 10.

Boeing is putting a new battery system on 50 of the 787s that have been delivered around the world. United's planes are being worked on at a Boeing facility in San Antonio, Texas.

Bing: See photos of the Boeing 787