The announcements come a day after United Airlines Flight 328 had to make an emergency landing at Denver International Airport after its right engine blew apart just after takeoff. Pieces of the casing of the engine, a Pratt & Whitney PW4000, rained down on suburban neighborhoods.
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The plane with 231 passengers and 10 crew on board landed safely, and nobody aboard or on the ground was reported hurt, authorities said.
The Federal Aviation Administration FAA Administrator Steve Dickson said in a statement Sunday that based on an initial review of safety data, inspectors "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."
The National Transportation Safety Board said in a separate statement that two of the engine's fan blades were fractured and the remainder of the fan blades "exhibited damage." The NTSB did caution that it was too early to draw conclusions about how the incident happened.
Video posted on Twitter showed the engine fully engulfed in flames as the plane flew through the air. Freeze frames from different video taken by a passenger sitting slightly in front of the engine and posted on Twitter appeared to show a broken fan blade in the engine.
United is the only U.S. airline with the Pratt & Whitney PW4000 in its fleet, the FAA said. United says it currently has 24 of the 777s in service.
United says it will work closely with the FAA and the NTSB "to determine any additional steps that are needed to ensure these aircraft meet our rigorous safety standards and can return to service."
The NTSB said the cockpit voice recorder and flight data recorder were transported to its lab in Washington for the data to be downloaded and analyzed. NTSB investigations can take up to a year or longer, although in major cases the agency generally releases some investigative material midway through the process.
Airlines in Japan and South Korea also operate planes with the Pratt & Whitney engine. Japan Airways and All Nippon Airways have decided to stop operating a combined 32 planes with that engine, according to Nikkei.
Nikkei reported that Japan's Ministry of Land, Infrastructure, Transport and Tourism also ordered the planes out of service, and the ministry said an engine in the same PW4000 family suffered unspecified trouble on a JAL 777 flying to Haneda from Naha on Dec. 4. It ordered stricter inspections in response.
United Airlines full statement:
"Starting immediately and out of an abundance of caution, we are voluntarily and temporarily removing 24 Boeing 777 aircraft powered by Pratt & Whitney 4000 series engines from our schedule. Since yesterday, we've been in touch with regulators at the NTSB and FAA and will continue to work closely with them to determine any additional steps that are needed to ensure these aircraft meet our rigorous safety standards and can return to service. As we swap out aircraft, we expect only a small number of customers to be inconvenienced.
Safety remains our highest priority - for our employees and our customers. That's why our pilots and flight attendants take part in extensive training to prepare and manage incidents like United flight 328. And we remain proud of their professionalism and steadfast dedication to safety in our day to day operations and when emergencies like this occur."
United officials said they currently have 52 of these aircrafts in their fleet, however, only 24 are active with the other 28 in storage.
NTSB Investigation Update: United Airlines Flight 328 Boeing 777 Engine Incident
Shortly after the NTSB was notified of the event, a senior NTSB investigator who lives in the Denver area began working with local law enforcement officials to coordinate the recovery of the components that separated from the engine, many of which landed in residential areas, according to board officials. Three other investigators from the NTSB's Denver regional office are assisting.
The NTSB investigator-in-charge for this event, along with a powerplant specialist, traveled from Washington to Denver Sunday morning, according to NTSB.
They said the initial examination of the airplane indicated most of the damage was confined to the number 2 engine; the airplane sustained minor damage. The examination and documentation of the airplane is ongoing.
The initial examination of the Pratt & Whitney PW4077 engine revealed:
-One fan blade was fractured near the root
-An adjacent fan blade was fractured about mid-span
-A portion of one blade was imbedded in the containment ring
-The remainder of the fan blades exhibited damage to the tips and leading edges
Investigators continue to examine the engine, airplane and the photographs and video taken by passengers aboard United flight 328, officials said Sunday night.
The cockpit voice recorder and flight data recorder were transported to the NTSB laboratory in Washington where each will be downloaded and analyzed.
The following initial investigative groups have been established by the investigator-in-charge:
Parties to the investigation include the Federal Aviation Administration, United Airlines, Boeing, Pratt & Whitney, the Air Line Pilots Association, and the Independent Brotherhood of Teamsters, NTSB said. Analysis of this event, along with conclusions and a determination of probable cause, will come at a later date when the final report on the investigation is completed, officials added.
This developing story will be updated.
The video featured is from a previous report.
ABC7 Chicago contributed to this article.