DENVER — United Airlines announced Sunday they will be grounding 24 Boeing 777 aircraft powered by Pratt & Whitney 4000 series engines, the same engine involved in Saturday's incident over the Denver suburb of Broomfield.
The Boeing 777-200, heading to Honolulu, experienced a right-engine failure shortly after takeoff. The plane turned around and returned to Denver International Airport, landing safely. The failure caused the engine's inlet and cowling to separate, raining debris onto a wide area of Broomfield, affecting homes and property in the Northmoor and Red Leaf neighborhoods. Nobody on board or on the ground was injured.
The airline, which currently has 52 of these aircraft in its fleet -- 24 active and 28 in storage -- said the move to remove Boeing 777s from its schedule comes "out of an abundance of caution." United Airlines is the only U.S. operator with this type of engine in its fleet.
United is not alone. Japan's Transport Ministry instructed Japan Airlines and All Nippon Airways, which operate aircraft equipped with the same series of engines, to ground the Boeing 777s in their fleet.
The Federal Aviation Administration is also taking action. Following the United Flight 328 incident, FAA Administrator Steve Dickson issued an Emergency Airworthiness Directive targeted at the Pratt & Whitney 4000 series-powered aircraft. The directive would require immediate or stepped-up inspections of Boeing 777 airplanes equipped with these engines.
"We reviewed all available safety data following yesterday’s incident. Based on the initial information, we concluded 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," Dickson wrote in a statement.
The FAA’s aviation safety experts are meeting with Pratt & Whitney and Boeing to finalize the details of the Airworthiness Directive. Exact details of the inspection will be specified in an emergency order.
Late Sunday, Boeing issues a statement on the incident: "Boeing is actively monitoring recent events related to United Airlines Flight 328. While the NTSB investigation is ongoing, we recommended suspending operations of the 69 in-service and 59 in-storage 777s powered by Pratt & Whitney 4000-112 engines until the FAA identifies the appropriate inspection protocol. Boeing supports the decision yesterday by the Japan Civil Aviation Bureau, and the FAA’s action today to suspend operations of 777 aircraft powered by Pratt & Whitney 4000-112 engines. We are working with these regulators as they take actions while these planes are on the ground and further inspections are conducted by Pratt & Whitney."
Investigators won’t know exactly what happened to the engine on Flight 328 until they tear the engine apart. But Tom Haueter, ABC News consultant and former NTSB Director of the Office of Aviation Safety, said it appears a fan blade could be the culprit.
"Looking at the photographs I’ve seen, it appears that a piece of one of the fan blades, those are the large blades you can see when you’re looking from the engine from outside, there’s a piece of a fan blade missing, and I can’t tell from another photograph if there’s another fan blade completely missing," Haueter said.
Initial findings from the NTSB appear to confirm Haueter's analysis. Investigators examining the Pratt & Whitney PW4077 engine on Flight 328 found extensive damage to the engine's fan blades.
Several Broomfield police officers spent a good part of Sunday morning looking for debris from the United Airlines flight. Pieces of the engine could still be seen on the ground, although in sometimes hard-to-find places.