“Everyone on our side flung open their windows just to see what it was,” Ms. Ebert said in a phone interview. “The casing to the engine had sort of flown off. There were pieces flying into the ocean, nuts and bolts flying out a little bit. A bolt hit the wing, and it just made this huge bam.”
Michael Nielson, seated in the middle section of the twin-engine Boeing 777, said flight attendants told passengers to return to their seats immediately and fasten their seatbelts. “The plane shook violently for the better part of five minutes,” he said in an email. Later, “the shaking subsided to constant, heavy vibration that stuck around for the rest of the flight.”
Ms. Ebert said the shaking was more intense than she had ever experienced, even on turbulent flights. “Back and forth, down one side and down to the other side,” she said. “The whole thing felt like it was a roller coaster going to go off the tracks.”
United said in an emailed statement that the plane, traveling from San Francisco to Honolulu, had made an emergency landing after the engine cowling, or covering, came off. “Our pilots followed all necessary protocols to safely land the aircraft,” it said. “The aircraft taxied to the gate and passengers deplaned normally.”
As the plane neared the runway, the flight attendants told passengers to brace for impact, hands against the seat in front of them. Some people began sobbing, Mr. Nielson said.
Around 12:40 p.m. local time, the plane touched down — surprisingly smoothly, Ms. Ebert said, and to a round of applause from passengers who had been screaming a few minutes before. Several went on to tweet photos and videos of the damage.
“Scariest flight of my life,” one wrote.
Similar malfunctions have happened before. In 2016, an American Airlines flight from Phoenix to San Francisco turned back after part of the engine cowling fell off. A JetBlue flight from Newark to Fort Lauderdale, Fla., did the same in 2010. And an Air France flight had to make an emergency landing in northern Canada last year after one of its engines exploded in midair.