Boeing has recommended that airlines ground all of its 777s with the type of engine that suffered a catastrophic failure over Denver. Meanwhile, U.S. regulators ordered United Airlines to step up inspections of those aircraft. United said Sunday it is temporarily removing the aircraft from service, a day after one of its planes made an emergency landing because its right engine blew apart just after takeoff. The engine was a Pratt & Whitney PW4000. U.S. Federal Aviation Administration Administrator Steve Dickson said in a statement Sunday that “the inspection interval should be stepped up for the hollow fan blades that are unique to this model of engine, used solely on Boeing 777 airplanes.” Japan also ordered the planes out of service, according to media reports.