Utility crews on Thursday worked to restore power to hundreds of thousands of homes and businesses in the US Northeast after a snow and ice storm slammed the region. But flights began returning to normal after thousands of delays or cancellations.The latest in a series of winter blasts dumped up to about a foot (30 cm) of snow on Wednesday and early Thursday on the Eastern Seaboard from Maryland to Maine. About 100 million people - or one-third of the US population, lives in the region.The storm coated roads with ice and broke tree limbs, knocking down power lines. At least four deaths were related to the storm, authorities said.Pennsylvania was the hardest hit. At one point, 849,000 customers were without power, according to the Pennsylvania Emergency Management Agency. By 8 a.m. EST (1300 GMT), utility crews had gotten number down to just over 500,000, the agency said."The storm that we had yesterday is pretty much done for Pennsylvania," said Craig Evanego, a forecaster with the National Weather Service in State College, Pennsylvania.