Disruptive pig kicked off flight

Passenger Robert Phelps took a picture after this passenger was asked to leave a USAirways flight with her "disruptive" pig.

• NEW: "It looked heavy. It was not a tiny, cute little pig," passenger says


• Passengers say a pig ran up and down aisle and left a foul mess


• Pig was allowed on flight as "emotional support animal," airline spokeswoman says


• DOT says animals that provide emotional support qualify as service animals in some cases

(CNN) -- A woman was kicked off a US Airways flight after the pig she brought for "emotional support" became disruptive, an airline spokeswoman told CNN.

The passenger and her large pig were booted from the flight before it left Connecticut's Bradley International Airport on Wednesday, spokeswoman Laura Masvidal said.

"After the animal became disruptive, the passenger was asked to deplane," she said.

How disruptive? Fellow passengers told the Hartford Courant that the big brown pig stank up the cabin of the tiny DC-bound aircraft before defecating in the aisle.

It was around 6 a.m. the day before Thanksgiving. When passenger Robert Phelps first saw the woman coming down the aisle, he thought she had a "really big dog" or a stuffed animal thrown over her shoulder.

"Everybody was trying to surmise what it could be because no one thought it was a pig," he told CNN. "Other than a Fellini movie, where would you see a person with a pig?"

After she reached her seat and began to stow her items, the pig began "dropping things" in the aisle, he said. As she tied him to the armrest and tried to clean up after him, he began to howl.

"She was talking to it like a person, saying it was being a jerk," he said. "I have no problems with babies, but this pig was letting out a howl."

A flight attendant asked her to move to the front of the plane, and eventually she left, he said. He took a photo of her as she walked past him.

"I understand dogs and cats on planes. They come in crates but this was way too big, and it had no container," he said. "It looked heavy. It was not a tiny, cute little pig."

The passenger was allowed to bring the pig on board as an "emotional support animal" under Department of Transportation guidelines.

"We follow all DOT guidelines," she said.

"Emotional support animals" have become increasingly popular in recent years, thanks in part to those guidelines.

In 2003, the DOT updated its policy regarding animals in air transportation to say "animals that assist persons with disabilities by providing emotional support" qualify as service animals.

It's up to airline personnel to determine whether an animal is a service animal. They can do so by seeking "credible verbal assurances," looking for physical indicators on the animal, such as a backup or identification tag, or by requesting documentation for service animals.

When it comes to emotional support animals, airlines may require supporting documentation from a mental health professional. The documentation should state that the passenger has a mental health-related disability and that "having the animal accompany the passenger is necessary to the passenger's mental health or treatment or to assist the passenger."

It is not clear whether the passenger on Wednesday's flight provided such documentation.