On a steamy summer evening, as the parking lot at Gravelly Point Park filled up and fishermen hovered beside the boat launch, several people looked into the sky and gasped.

A dark blue US Airways jet was hurtling toward the runway of Reagan National Airport, where a white plane was still taxiing before takeoff. At the last moment, the blue plane lurched up and arced back into the sky.

Disaster averted? Kevin Cordwell, a 27-year-old payroll specialist on Capitol Hill who was sitting on a grassy bluff nearby, shook his head. A recreational pilot and an avid plane spotter since childhood, he'd seen this before. The white plane had gotten a late start, he explained, and the other pilot didn't want to take any chances.

"He looked at it and said, 'If anything happens to that plane and it can't take off, I'm going to hit it,' " Cordwell said. "I've had to do it myself."

His words were drowned out by a roar and a whoosh. A hulking plane bore down, then dropped onto the runway.

Gravelly Point, which lies between George Washington Memorial Parkway and the Potomac River, means many things to the many people who flock here on summer evenings. With its unimpeded view of the runway, it attracts airplane aficionados, who can sidle in close to the belly of a moving jet without getting landed on. Sports teams compete on its playing fields. Couples embrace in its parking lot. Cyclists and joggers breeze by on its footpath. Heads tip up each time a plane swoops by (depending on wind direction, they either land or take off over the park).

For Cordwell, it is a place to watch the intricate dance of runway patterns and get his mind off work. For his co-worker Shelly Jennings, 36, sitting beside him on the grass, it is a place to listen and learn. Some planes have upturned wing tips that pilots have nicknamed epaulets, Cordwell told her. The epaulets keep air pressure on the plane and reduce fuel consumption. The sleek Embraer 170s are new to the market; the Super 80s often have a black nose cone.

"What is that?" Cordwell asked as something screamed past.

Jennings smiled and squinted. "This would be, um, an F-100?"

"Right! You got it. You're learning."

Elsewhere in the park, as a pink sun hovered above the tree line, Julia Warner, 29, a congressional staff member from Arlington, hardly noticed the planes. Watching her coed Ultimate Frisbee team, Blue Steel, race around in the heavy air, she said, "When we're playing . . . I think we just tune them out."

She does, however, have a pet scientific phenomenon. "Have you noticed the vortex?"

The what?

The sound that comes after a plane passes. "It's the differential in wind speed from the plane pulling the wind behind it. The slower wind collapses around it," she said. After the next plane, she frowned and listened. Nothing. Another plane, still nothing. Then Blue Steel's captain called the players over for a pep talk and Warner excused herself, saying, "Make sure you hear the vortex before you leave."

Back by the runway, past the students from Darfur, Sudan, swinging a toddler around and past the lone Salvadoran waiting for his friends to play soccer, Be Pham, a 61-year-old deliveryman from Falls Church, gazed at the glittering airstrip.

Pham's wife, Tu, cutting a watermelon on a blanket on the grass, smiled and said something in Vietnamese. "My mom said he thinks about the war," their son Long Pham, 19, said, "and he's kind of sad because the communists took over."

Pham, a pharmacology student at Northern Virginia Community College, said his family's weekly visits to the park have special meaning to him. This airport was where, in 1994, he landed and first met his father, a former general in the South Vietnam army who had been imprisoned in Vietnam and later escaped the country, eventually arriving in the United States. Pham's mother had been pregnant with him when his father left, and it was eight years before she could bring him and his older brother to America. "I kind of had a weird feeling," Pham said, recalling that day. "And then I started crying."

Several feet away, four young women stood at the water's edge in saris the colors of tropical flowers. Three days earlier, after 15 years of immigration paperwork, they and their mother had arrived from Pakistan. Their father, a real estate agent in Annandale, had been coming here once a week for years, awaiting the day when it would be their plane landing.

Now his family sat around him on their first big outing. "Maybe next time I'll take them to the Smithsonian or the Lincoln Memorial," said the father, Amjad Khan, 57. For now, their grins as they watched the planes, with the U.S. Capitol lighted up and the Washington Monument rising behind them, were enough.

"It is more than our expectations," said his daughter Saima Amjad, 22.

"The landing," said daughter Sara Amjad, 25, "is fabulous."

Another plane receded into the darkening haze. A moment later came a high, ruffly sound, like a bird shaking its wings in a fountain.

It was the vortex.

"When we're playing . . . I think we just tune them out," a member of the Blue Steel Ultimate Frisbee team says of planes over the park. Depending on wind direction, jetliners either land or take off over Gravelly Point Park.Capitol Hill staffer Kevin Cordwell, a recreational pilot and an avid plane spotter, shares aviation trivia with co-worker Shelly Jennings as jetliners take off and land at Reagan National Airport.Kanjam Omar, 2, clutches a leg of father Seifeddine Koko, a native of Darfur, Sudan, as a plane roars overhead at Gravelly Point Park.