Investigation into why flight UA328’s engine failed on Boeing 777

Federal investigators are looking into what caused an uncontained, catastrophic engine failure on a United Airlines flight bound for Honolulu, Hawaii, that left Denver a half-hour late on Saturday and proceeded to drop large chunks of debris on a northern suburb and park before landing safely back at Denver International Airport.

No injuries were reported as of Sunday morning — neither among the 231 passengers or 10 crew members, nor anyone in Broomfield, about 25 miles northwest of the airport.

The right engine failure, which authorities have not provided any details for the cause of the malfunction, was described as an explosion both on the ground and from passengers.

“My wife and I were sitting in the living room, reading the paper, when we heard a loud bang,’ ” Broomfield homeowner Kirby Klements said Saturday, standing in front of the engine ring, which was taller than him and destroyed the cab of his truck. “First, I thought it was debris from a trampoline from my neighbor’s yard. Came out and looked at it and knew right away that it was the front of an engine of an airplane.”

Broomfield police said debris landed in Commons Park — where soccer practice was going on — and in at least two neighborhoods. Police spokeswoman Rachel Welte said that the department was “securing the scene and all the debris” for the National Transportation Safety Board (NTSB), which is investigating the major malfunction and aftermath.

Heather Solar and the girls team she coaches were among a half-dozen teams practicing at Commons Park on Saturday afternoon when she heard the noise. A large piece from the plane fell 10 feet from where she was standing. She and the other coaches told their players to grab their bags, cover their heads and run either to their cars or to the nearby park shelters.

“Honestly, what I thought it was first … I thought we were being bombed,” Solar said. “There was so much debris in the sky.”

David Delucia, who is from Fort Lauderdale, Fla., and his wife were on the Boeing 777-200 wide-body airliner, and said the plane began to lose altitude right after the sound of the engine exploding.

“Everything started shaking, like the worst turbulence you can imagine,” he told The Post on Saturday. “When we started to descend, we started going down through the clouds. People were saying that they were dumping fuel while it was going on. … We were getting information (from passengers) on the right side that it was on fire all the way ’til we landed.”