The loud boom was unmistakable aboard United Airlines Flight 328 just after take-off on Saturday. Something had clearly gone very wrong.
Some of the 241 people on the flight from Denver International Airport to Honolulu opened their windows to see an exposed engine spewing flames and pieces of the plane falling away.
Others closed their windows, grabbed their loved ones and prayed. Thousands of metres below in a Denver suburb, people on the ground ran to shelter to dodge debris suddenly plummeting to the earth.
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The pilots issued a mayday call and, after turning back to the airport, landed the plane safely. Remarkably, there were no reports of injuries either in the air or on the ground. Still, interviews with passengers show the incident provided a huge scare for everyone involved.
The plane landed safely at Denver International Airport, and no one on board or on the ground was hurt, authorities said. But both those in the air and on the ground were deeply shaken.
'There was a big boom'
Travis Loock, a passenger on Flight 328, said it was about 20 minutes after take-off for Honolulu that he heard a boom.
"There was a big boom and the kind of sound you don't want to hear when you're on the airplane," Mr Loock, who was flying with his wife, said in a phone call.
"And I instantly put my shade up, and I was pretty frightened to see that the, the engine on my side was missing."
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"We were just glad we weren't over the ocean, because that's where we were heading," he said.
Mr Loock said he could sense the fear on the plane, but everyone was "very calm."
"A lot of people couldn't see the engine on that side, right, so I was a little more freaked out because I could see it, and I knew that was not right," he said.
"When it initially happened, I thought we were done. I thought we were going down," said passenger David Delucia, who stuffed his wallet in his pocket so he could be easily identified if the plane did go down.
"The pilot did an amazing job. It was pretty unnerving."
Nate Fisher heard the sound, too. "I thought lightning struck the plane at first," he said.
When Bob Brown heard the explosion, he looked out his window, saw the damage to the engine and took out his phone to film it.
"We looked at each other, my wife and I, held hands, and just wished our kids that we'd see them again," he said.
Mike Vena was in the middle of the plane when he heard the explosion. "The plane just started shuddering and it was that way for about a half an hour until the plane landed," he said.
Brenda Dohn, who was traveling with her children, saw smoke outside the window and knew something wasn't right.
"My daughter was sitting on the window and I was just like, 'Don't look, let's close it up, and let's just pray,'" she said.
"So that's what we did. We kind of just held hands and said some prayers."
What those on the ground did
While those in the air stressed about the landing, those on the ground looked up to see debris falling from the sky.
The large circular covering to the jet engine fell just next to a home, but thankfully missed causing more serious damage.
Kirby Klements, the homeowner, said he thought his neighbour's trampoline had blown over to his yard.
"But as soon as I open the door, I go, 'that is the front engine of a plane,'" Mr Klements said.
Kieran Cain said he was playing with his children at a local school when a plane flew over and they heard a loud boom.
"We saw it go over, we heard the big explosion, we looked up, there was black smoke in the sky," Mr Cain said.
"Debris started raining down, which you know, sort of looked like it was floating down and not very heavy, but actually now looking at it, it's giant metal pieces all over the place," he said.
The Broomfield Police Department posted photos on Twitter showing large, circular pieces of debris that appeared to be the engine cowling leaning against a house in the suburb about 40 kilometres northwest of Denver.
Police asked anyone injured on the ground to come forward.
The US Federal Aviation Administration said in a statement that the plane experienced a right-engine failure shortly after takeoff.
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.
The US National Transportation Safety Board is investigating. Authorities have not released any details about what may have caused the failure.
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.
