An engine fan blade from United Flight 328 Saturday has damage consistent with metal fatigue, a preliminary examination by the National Transportation Safety Board (NTSB) has shown.
The blade, which was recovered on the ground in the Denver suburb of Broomfield, Colo., was to get a closer examination Tuesday in a laboratory owned by engine maker Pratt & Whitney, NTSB chairman Robert Sumwalt said.
The blade was one of two that fractured shortly after takeoff on the Denver-Honolulu flight. The Boeing 777-200 returned to Denver Airport without any injuries. United has since grounded the 24 777s powered by the same Pratt & Whitney 4000 series engines that it had been operating prior to the weekend. No other U.S. carrier has that aircraft/engine combination in its fleet. Airlines around the world that do fly that combination have also grounded the planes.
The fan blade, which is now at the Pratt & Whitney laboratory, was fractured at its base, while the other fractured blade was damaged in its midsection and was found lodged within the engine's containment ring. That second blade, said Sumwalt, was probably severed by the first blade after it broke loose.
Sumwalt said NTSB investigators will remove the entire engine from the aircraft and tear it down as part of its investigation into the incident. The NTSB will also examine United's maintenance history of the engine and the aircraft.
"Our mission is to understand not only what happened, but why it happened so that we can keep it from happening again," Sumwalt said.