Boeing has recommended that airlines ground all 777s with the type of engine that suffered a catastrophic failure over Denver this weekend, as US regulators ordered United Airlines to step up inspections of those planes. Several airlines, including United, said they were temporarily removing the aircraft from service after one of the American carrier's planes made an emergency landing at Denver International Airport Saturday because its right engine blew apart just after take off. Pieces of the casing of the engine, a Pratt & Whitney PW4000, rained down on suburban neighbourhoods. None of the 231 passengers or 10 crew on board were hurt, and the plane landed safely, authorities said.