Investigations of aircraft accidents and incidents can take more than a year, but officials usually get an early read on factors that may have played a role.
On Monday, two days after the high profile engine malfunction on United Airlines Flight 328 from Denver to Honolulu, the National Transportation Safety Board held its first briefing on the incident, highlighting possible metal fatigue to an engine fan blade and documenting a loud bang heard on the cockpit voice recorder.
NTSB Chairman Robert Sumwalt gave details on how the in-flight emergency unfolded and offered preliminary findings.
Approximately four minutes after takeoff from Denver International Airport early Saturday afternoon, when the aircraft was at 12,500 feet and cruising at 280 knots, a loud bang was heard on the cockpit voice recorder and increased vibrations were recorded on the affected engine.
The pilots declared an emergency with air traffic controllers and began a critical in-flight checklist, including the shut down of the engine.
Boeing 777 grounding explained, visually that the Pratt and Whitney engine failure involved two incidents on the same day.
The plane’s condition didn’t need an immediate evacuation upon landing, and after passengers deplaned, it was taken to a nearby United hangar for examination.
Pieces from the plane, including those that fell from the sky across Bloomfield, Colorado, are now laid out on the floor of the hangar.
The cockpit voice recorder and flight data recorders were sent for analysis to NTSB facilities in Washington, DC.
Two of the 22 fan blades on one of the Pratt and Whitney engines were damaged. One fan blade separated at the root and the other was fractured in the middle, likely getting struck as the other blade was separating.
One of the pieces was discovered in a soccer field in Broomfield, a Denver suburb. A preliminary examination of the fractured fan blade exhibits signs of damage consistent with metal fatigue.
The signs were so-called beach marks or crack arrest marks that can usually be seen with the naked eye. Sumwalt compared it to marks left during tides.
He said it’s like if the ocean comes in and goes back out, you’re going to see a mark where the ocean was.
United Airlines engine failure on Boeing 777 flight to Hawaii – what travellers need to know.
The fractured fan blade was being flown overnight by a private plane to Pratt and Whitney facilities for examination.
Of course, it’s good to hear that everyone on the aircraft is safe, and, fortunately, no one on the ground was hurt or killed from the large debris that came down.