The most famous incident occurred on Valentine’s Day, when JetBlue melted down during an ice storm at Kennedy Airport. JetBlue began canceling flights—1,100 over several days. Thousands of passengers were kept on parked planes for up to 11 hours. Others were stuck at airports for days. Similar incidents have been occurring routinely in a system stretched beyond the breaking point.

When aircraft are stranded, conditions quickly deteriorate. Air quality becomes poor. Food runs out. (On many of these flights, passengers have informally organized to share what snacks they had, typically ensuring that children, the elderly, the ill, and others with special needs receive priority.) And worse.

“Who can ever forget the ‘Dog Poop Plane’?” Hanni said. That was the flight on which a panicked dog defecated on a stranger in the next seat. Also legendary is the “Barf-Bag Flight,” during which a woman, ill after hours of confinement, threw up into a vomit bag, and was angrily told by a flight attendant to hold the bag because there was no place to discard it.

As hours go by, lavatories become filthy and in some cases reach capacity. On one flight, waste overflowed onto the feet of nearby passengers. “One unfortunate lady was wearing flip-flops,” Hanni said.

Hanni will spend most of this month in Washington. On September 26, she is scheduled to give testimony at new hearings on airline service by the House Aviation Subcommittee, where a version of the Passengers’ Bill of Rights was introduced last spring by her congressman, Representative Mike Thompson. A similar bill, introduced by senators Barbara Boxer of California and Olympia Snowe of Maine, is under consideration in the Senate. Airlines, meanwhile, are lobbying fiercely against any federal legislation, insisting that they can police themselves.

Six months before she was stranded, while still working as a real estate agent, Hanni was brutally assaulted by a man who posed as a potential client and arranged a meeting in a home that was for sale. The ordeal “riveted in my mind how horrible the feeling of powerlessness is,” she says. “In a different but still important way, being stranded on an airplane for a long time is being powerless, and I decided, at least in this case, I could do something about it.”

Wednesday’s Strand-In has attracted national attention, mostly because of Hanni’s knack for publicity, coupled with the novelty of the tent on the Mall. Volunteers plan to go all out to demonstrate the woeful conditions on a stranded plane, sitting in two-by-two rows of folding chairs separated by a narrow aisle. “A flight attendant donated six uniforms, so some of us will be wearing them,” Hanni said. After learning from her son that there was a novelty “stink spray” that could help recreate the smell of a stranded plane, she purchased some containers.

Several members of Congress are expected to speak at the Strand-In, including representatives Mike Thompson (Democrat, California), Ron Klein (Democrat, Florida), and John Hall (Democrat, New York), Hanni said. One pilot for a major airline, G. Bruce Hedlund, agreed to speak after meeting Hanni in California. (Under company policy, Hedlund can speak freely but can’t identify his airline.)

“People forget that in these instances, the pilots are also prisoners,” says Hedlund, who has been flying commercial jets for about 25 years. “I told Kate that I had some concerns about how legislation could affect the authority of the airline captain. . . . She’s open to other people’s ideas, so I agreed to talk. I said ‘I’ll need 30 minutes,’ and she said, ‘How about two?’ ”