United Airlines is getting its 787s back in the air.

The planes are returning after being grounded for four months by the federal government because of smoldering batteries on 787s owned by other airlines. The incidents included an emergency landing of one plane, and a fire on another.

The incidents never caused any serious injuries. But the January grounding embarrassed Boeing, which makes the 787, and disrupted schedules at the eight airlines that were flying the planes. The company had delivered 50 of the planes worldwide.

The grounding forced United to delay planned international flights and hurt its first-quarter earnings by $11 million. Others, including Japan Airlines and South America's LATAM Airlines Group, also said profits were reduced. LATAM said it still had to make payments on the plane and pay for crews and maintenance. It expects to resume flying soon.

United's first 787 flight was scheduled for 11 a.m. Monday from Houston to Chicago.

Passengers didn't appear to be too worried. "We saw strong demand for the flight from the first weekend it opened for sale," United spokeswoman Christen David said.

United is planning to use 787s on shorter domestic flights before resuming international flights on June 10 with new Denver-to-Tokyo service as well as temporary Houston-to-London flights. It's adding flights to Tokyo, Shanghai, and Lagos, Nigeria, in August.

Those long international flights are the main reason the 787 exists. Its medium size and fuel efficiency are a good fit for long routes. Starting with shorter domestic flights "will give us a period to ramp up full 787 operations," David said.

United Continental Holdings Inc. was the first U.S. airline to get the 787 and now has six. United has said it expects to have four fixed by Monday, with the other two getting their batteries modified in coming days.

The 787 uses more electricity than any other jet. And it makes more use of lithium-ion batteries than any other jet, because it needs to be able to provide power for things like flight controls and a backup generator when its engines are shut down. Each 787 has two of the batteries.

Boeing Co. never did figure out the root cause of the battery incidents. Instead, it redesigned the battery and its charger. The idea was to eliminate all of the possible causes, 787 chief engineer Mike Sinnett said in an online chat on Thursday where he and a Boeing test pilot took questions about the plane.

The changes include more heat insulation between each cell and charging the battery to a lower maximum voltage.