DENVER (AP/CBS4) – Aviation safety experts said United Airlines Flight 328 appeared to have suffered an uncontained and catastrophic engine failure on Saturday over the Denver metro area. The Federal Aviation Administration said in a statement that the Boeing 777-200 returned to Denver International Airport after experiencing a right-engine failure shortly after takeoff and no one was hurt.

(credit: CBS)

Flight 328 was flying from Denver to Honolulu when the incident occurred and debris fell into neighborhoods in Broomfield but no one on the ground was injured.

READ MORE: Plane Debris Falls From Sky & Onto Broomfield Neighborhoods

Such an event is extremely rare and happens when huge spinning discs inside the engine suffer some sort of failure and breach the armored casing around the engine that is designed to contain the damage, said John Cox, an aviation safety expert and retired airline pilot who runs an aviation safety consulting firm called Safety Operating Systems.

“That unbalanced disk has a lot of force in it, and it’s spinning at several thousand rotations per minute … and when you have that much centrifugal force, it has to go somewhere,” he said in a phone interview with the Associated Press.

Pilots practice how to deal with such an event frequently and would have immediately shut off anything flammable in the engine, including fuel and hydraulic fluid, using a single switch, Cox said.

An airplane that appears to have smoke trailing from its right side seen heading east towards Denver International Airport — seen from Montview Boulevard and Peoria Street. (credit: Andy Cross/MediaNews Group/The Denver Post via Getty Images)

Former NTSB Chairman Jim Hall called the incident another example of “cracks in our culture in aviation safety (that) need to be addressed.

Hall, who was on the board from 1994 to 2001, has criticized the FAA over the past decade as “drifting toward letting the manufacturers provide the aviation oversight that the public was paying for.” That goes especially for Boeing, he said.

READ MORE: PHOTO GALLERY: Plane Debris Falls Onto Broomfield

Despite the scary appearance of a flaming engine, most such incidents don’t result in loss of life, Cox said.

The last fatality on a U.S. airline flight involved such an engine failure on a Southwest Airlines flight from New York to Dallas in April 2018. A passenger was killed when the engine disintegrated more than 30,000 feet above Pennsylvania and debris struck the plane, breaking the window next to her seat. She was forced halfway out the window before other passengers pulled her back inside.

In that case, the breakdown was blamed on a broken fan blade in an engine of the Boeing 737. The Federal Aviation Administration ordered airlines to step up inspections of fan blades on certain engines made by CFM International, a joint venture of General Electric and France’s Safran S.A.

In 2010, a Qantas Airbus A380 suffered a frightening uncontained engine failure shortly after takeoff from Singapore. Shrapnel from the engine damaged critical systems on the plane, but pilots were able to land safely. The incident was blamed on the faulty manufacturing of a pipe in the Rolls Royce engine.

“The flames scare the hell out of everybody. But they are the least of the problem because you’re going to get them put out and you’re going to shut off everything that can burn,” Cox said.

(© Copyright 2021 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)