Business-class fliers love sliding doors — but they’re causing a nuisance for airlines and planemakers

The Polaris suites in a United Airlines Boeing 787. Courtesy of United Airlines The rise in premium travel is causing frustrations for airlines and manufacturers. Fancy new business-class seats need to go through rigorous certification testing. Airplanes have been stuck at factories or flown with empty business class cabins. More travelers are shelling out for the best airplane seats amid a boom in premium travel, driving airlines to develop increasingly complex business-class seats — some of…