When Elisabeth Haas took her window seat on an American Airlines flight from Orlando to Dallas, she discovered a problem — a very big problem.

"A morbidly obese seatmate encroached into my personal space," she says. "He required a seat belt extender and that the arm rest divider be raised to accommodate his girth during the entire flight, including takeoff and landing. He also had to walk down the aisle oriented sideways and moved quite slowly."

The problem of XL passengers on planes is hardly new, but their interactions with other passengers are creating a lot more friction lately. I know because over the American Thanksgiving holiday week, I reported about a man who says he had to stand on a flight between Anchorage, Alaska, and Philadelphia, and it became the talk of the town for about half a news cycle.

I heard from lots of passengers who said they, too, have tussled with oversized seatmates.

Haas, who was returning from a trip to see her dying grandmother in Florida, says she couldn't comfortably fit in her seat or stow her luggage under her seat because of the encroachment. She had access to only about one-third of her economy-class seat for the duration of the flight.

"Do you understand the horrific discomfort of feeling someone's massive, unrelenting, hot and sweaty flesh pressed into your body from shoulder to ankle?" she asks.

The American Airlines flight attendants were compassionate, and because it was a sold-out flight, they allowed her to sit in their jump seats. But when she wrote a polite letter suggesting that American Airlines change its rules to prevent this kind of thing from happening again, the best the airline could manage was to reply with a form letter.

"We are sorry for your discomfort on your recent flight with us to Dallas/Fort Worth," the airline wrote. "Our airport personnel must walk a fine line in order to satisfy the needs and rights of all of our customers. I am disappointed to hear that we were not more successful on this occasion, and I am genuinely sorry that the enjoyment of your flight was diminished as a result."

American Airlines didn't address any of her safety concerns, nor did it pledge to change its rules.

Airline policies on XL passengers are at best, amorphous. Only Southwest Airlines has a clearly defined and well-publicized policy — it calls them "customers of size" — but the other major airlines tend to dance around the issue. It's hard to find their policies online, and they seem to be unevenly enforced.

When airlines do talk about their weighty customers, they do so as in gentle tones, as if at any moment, these big passengers could shatter into a thousand pieces because someone called them fat.

But the focus is on the wrong person. It isn't the morbidly obese who are in need of special protection, but the folks seated next to them. When the armrest is up, it can mean serious trouble for the other guy.

Norman Chance was the other guy on a recent flight between Anchorage and Chicago. Like Haas, he had a window seat in economy class but found himself next to two "very large" people in the seats next to him.

"I had to sit sideways for the entire flight, in agony and pain," says Chance, who owns an aviation company in Indianapolis. "They both fell asleep and would not move despite my requests. I ended up injuring my back, which was only resolved after visits to a chiropractor."

He's angry that airlines can allow two XL passengers to fly in economy-class seats that are obviously too small, and he and Haas are upset that there isn't a law to prevent a situation like this from repeating itself.

There are no rules about passengers having to fit into the economy-class seats. The closest the Federal Aviation Administration comes to addressing this issue is when it issues its guidance on passengers with disabilities, but it doesn't specifically classify a passenger's weight or size as a disability that is in need of protection. If it did, airlines would probably have to give every tall guy like me a first-class seat, which, now that I think about it, wouldn't be so bad.

But I think we'd all settle for a rule that says passengers are entitled to a minimum amount of legroom and personal space, whether they're on American Airlines or any other airline. Such a rule would prevent a bulk of these XL passenger incidents from happening, and make flying a far more humane experience — for all of us.

Christopher Elliott is the ombudsman for National Geographic Traveler magazine. You can read more travel tips on his blog, elliott.org, or email him with questions at celliott@ngs.org.