NEW YORK —The investigation into the engine failure of a Boeing 777 could take more than a year, officials said, but already the picture is becoming clearer about what happened to the United Airlines flight on Saturday. According to investigators, the Pratt & Whitney engine failed minutes into United Airlines flight 328, headed from Colorado to Hawaii, leaving a mile of debris in its wake. After the incident, United grounded all of its Boeing 777s powered by PW4000 series engines. A preliminary investigation indicates the damage was "consistent with metal fatigue," according to information from the National Transportation Safety Board (NTSB), which has prompted federal regulators to reexamine engine inspections. "Pratt & Whitney is actively coordinating with operators and regulators to support the revised inspection interval of the Pratt & Whitney PW4000 engines that power Boeing 777 aircraft," the company said. "Any further investigative updates regarding this event will be at the discretion of the NTSB. Pratt & Whitney will continue to work to ensure the safe operation of the fleet." Both the Federal Aviation Administration (FAA) and the NTSB are investigating the incident. Here is what we know so far. What happened on the flight "United 328 Heavy — Mayday Mayday ... Denver departure. United 328 Heavy Mayday. Aircraft just experienced engine failure — need to turn immediately," the air traffic audio from the plane rang out on Saturday. The PW4000 engine has 22 blades, investigators said, one of which was found lodged inside the jet engine"s containment ring. Another was found in a soccer field in Broomfield, Colorado. One of the blades in the plane"s right engine broke free at the hub, likely hitting another that was broken mid-span, investigators said Monday. The former shows damage "consistent with metal fatigue," NTSB Chairman Robert Sumwalt said. The flight fuselage also had damage to a non-critical composite piece designed to make the plane more aerodynamic, Sumwalt said. On the plane, passengers saw the engine completely stripped of its outer casing, according to video from passenger Travis Loock. The mood was tense, Loock told CNN, but everyone was "very calm" on board as the pilot came on to say they would be landing in four minutes. "My daughter was sitting on the window and ... I was just like, "don"t look, like let"s let"s close it up and let"s just pray,"" passenger Brenda Dohn said. None of the passengers were injured. Nor were residents around Broomfield from the falling debris that stretched a mile. "We dispatched police officers and within minutes we actually were on scene of some of these homes, and we actually saw some of these large pieces of debris," Broomfield Police spokesperson Rachel Welte told reporters on Saturday. — Courtesy photo