(CNN) -- Nearly three hours after the crash, David Eun walked through customs at San Francisco International Airport. By then, the adrenaline rush was subsiding enough that he could begin processing the enormity of it all.
He'd just survived a catastrophe.
The Samsung executive describes himself on his Twitter profile as being an "all-American Korean" a "pensive optimist" and a frequent flier.
He's used to getting on planes and crossing the Pacific. He'd been at the same airport in April for a weeklong trip to Seoul, where Samsung is headquartered.
Asiana Flight 214 might have been just another plane ride for Eun. Instead, the tech savvy businessman found himself bracing for life as something went terribly wrong in the landing. And he tweeted the experience.
"I just crash landed at SFO. Tail ripped off. Most everyone seems fine. I'm ok. Surreal ..."
Other passengers on the plane described a harrowing experience.
Elliott Stone could see the tarmac below him. The angle of descent seemed too sharp. The pilot tried to raise it at the last minute, said another passenger.
"And then right when it appeared to coast for the landing, all of a sudden the engine was off, like you sped up, like the pilot knew he was short. And then the back end just hit and flies up in the air and everybody's head goes up to the ceiling."
He said the back of the plane broke off. That's where several flight attendants were sitting.
Several people watched the plane crash from the airport or other nearby areas. Still others saw it up close, sitting in other planes on the tarmac. For them it was like watching a frightening movie. Only, it was all real.
Witnesses describe unusual landing
Everything looked normal at first. The plane was coming into the airport Saturday in a routine flight pattern. But then the wheels seemed too low too soon, said Dan Glickman.
When a plane lands, there is typically white smoke from the friction of the wheels. But there was a large plume of white smoke when Flight 214 touched down. Then people heard a pop and a fireball burst out from underneath the aircraft.
"It just pancaked immediately. It collapsed and then it slid," Glickman told CNN affiliate KTVU. "It just kept sliding and sliding and sliding. I was surprised it didn't come apart. It was unreal."
Danielle Wells also saw the plane go down.
"Literally just witnessed a plane crash start to finish. I cannot stop crying I can't believe this," she said on Twitter.
Kristina Stapchuck saw the crash from a window seat on another plane. She saw Flight 214 rock back and forth and the tail come off. Other parts came off and shattered everywhere on the runway. It looked like the plane was sliding on its belly all the way down the runway.
"It all happened so suddenly," she said.
People who watched it happen feared the worst. They could see the inside of the plane in orange glow from the fire. Smoke was billowing from the plane. One passenger on the plane shot a photograph that showed flames and smoke bursting out of the plane's windows.
Those outside thought it was instant death for everyone aboard. Flames and smoke were bursting out of many of the aircraft's windows.
Passengers dashed from aircraft
Eunice Bird Rah's father was on Flight 214. He sent her text messages telling her he was fine. He didn't want her to worry so he chose his words carefully.
"I think ... he didn't want me to know the full-on details of what was going on around him," Rah said.
Passengers huddled together and pushed open emergency exit doors, Stone said. Some didn't bother to use evacuation slides; they jumped directly out onto the tarmac to save themselves.
Ben Levy helped people out even though he had broken ribs. He tweeted a photo of fellow passengers sitting atop their bags. Behind them, the Asiana jet sat consumed in smoke.
At the airport, witnesses said they could see people running out.
"I was happy to see that some people were running out," said one man. "Then I went, 'Oh my god, some people lived.'
Then emergency responders and firefighters were all over the tarmac.
"They're evacuating the injured," Eun tweeted again. "Haven't felt this way since 9/11."
He was one of the lucky ones aboard Saturday. There were 291 passengers and 16 crew members on Flight 214.
"Friends, pls don't call right now. I'm fine," he tweeted.
"Most people are totally calm and trying to let the fire and rescue do their jobs," he said. "Just like during 9/11, most people are great and try to be helpful in crisis..."
The charred carcass of the jet was still on the runway. Many of Eun's fellow passengers were in Bay Area hospitals.
When he finally left customs, Eun began to think about it all -- and about all the people he cherished.
CNN's Wolf Blitzer and Don Lemon contributed to this report.