Flight 93 was en route from Newark, N.J., to San Francisco when it went down about 10 a.m. near an overgrown strip mine about 35 miles from the Maryland line. Pennsylvania state police said they did not expect to find any survivors.
James P. Moran Jr., a Democrat from Virginia, said he was told the terrorists planned to strike Camp David, the presidential retreat in the Catoctin Mountains in northern Frederick County. Officials later dismissed the claim, saying it was first advanced as a theory.
Flight 93 left Newark at 8:01 a.m. with 38 passengers, two pilots and five flight attendants. No names have yet been released, but authorities said they were planning to take families of the victims to the site as soon as possible.
The call lasted about one minute, and the caller said repeatedly, "We are being hijacked," said Stevens.
Westmoreland dispatch supervisor Glenn Cramer told the Associated Press that the caller was a man who had locked himself in a restroom on Flight 93. The caller said the plane "was going down," Cramer said. "He [the caller] heard some sort of explosion and saw white smoke coming from the plane, and we lost contact with him."
Paula Pluta, a self-employed sales consultant who lives near the crash site, was watching television and had not heard about the attacks in New York and Washington when the plane passed over her house.
"I heard a rumble, a roar, and screeching," she said. "I was sure something was falling out of the sky."
Pluta ran to her porch and saw the plane dive at a steep angle over the trees outside her house. The crash sent a fireball 100 feet into the air and shook her house, she said.
She rushed to the site and found a crater with thousands of pieces of metal in it, none of them larger, she said, than the small American flag stuck in her flower pot.
"I wouldn't have known what it was," she said.
The impact crater is 8 to 10 feet deep and 15 to 20 feet long, said Capt. Frank Monaco of the Pennsylvania State Police.
"It obviously appears to be a very high impact into the earth," said Jeff Killeen, an FBI public information officer at the scene.
Bruce Grine's service station is 2 miles from the crash site, but he felt the impact of the crash.
"It shook the whole station," he told the AP. "Everyone ran outside, and by that time the fire whistle was blowing."
Mark Stahl of Somerset was listening to news accounts of the terrorist attacks in New York and Washington when he heard the crash.
He grabbed his camera and ran to the scene.
"There is a crater gouged in the earth, and the plane is pretty much disintegrated," he told the AP. "There's nothing left but scorched trees."
About 5:30 p.m., a United Airlines 727 arrived at nearby John Murtha Johnstown-Cambria County Airport with recovery equipment that was transferred into a 13-car caravan and taken to the scene.
At the Cambria County airport, air traffic controllers said they received word from Cleveland shortly before 10 a.m. that a suspicious airplane was headed for Johnstown, flying much lower than it should be. They evacuated the airport except for two control-room employees, but had trouble locating the plane.
"It had to be extremely low for an airplane to be 15 miles out and for us not to spot it," said air traffic manager Dennis Fritz. "That's extremely unusual."
According to the AP, control tower employees made radio contact with the airliner, but the pilot refused to identify himself. Moments later, the plane crashed.
Sun staff writer Sheridan Lyons contributed to this article.