Rules that cause friction between flight attendants and travelers often involve electronic devices and carry-on bags. But as carriers invest more money in amenities for higher-paying customers, stricter divisions between passenger classes contribute to the tension. (Read more: Will iPads Revolutionize In-Flight Entertainment)
Veda Shook, international president of the Association of Flight Attendants-CWA, said she was not aware of a policy limiting where passengers could walk, especially if a cart was blocking an aisle or a family member was seated on the other side of the plane.
"I think it's generally understood that you hang out in the cabin that you're in," she said. "But I've never really encountered a situation where someone couldn't move about the cabin to get from point A to B."
Given the potential consequences of a disruptive event, Ms. Shook said, flight attendants are trained to avoid any escalation of conflict, a "nip it in the bud" approach that may seem aggressive.
"You have to be prepared to shut anything down immediately," she said.
Airlines report to the F.A.A. incidents involving "unruly passengers" who interfere with the duties of a crew member. The agency said there were 101 such incidents in 2012, well below the 140 to 176 reports in each of the previous three years. The statistics do not include security violations, which are handled by the Transportation Security Administration.
David Castelveter, a T.S.A. spokesman, said the agency could not comment on the incident involving Mr. Pollock. But in an e-mail message, Mr. Castelveter explained: "Federal air marshals are trained to protect the safety and integrity of the aircrew, passengers and aircraft. Due to the sensitive nature of their job, T.S.A. cannot discuss specific tactics or training."
The Federal Air Marshal Service operates largely out of public view, but the secrecy surrounding its operations can put travelers in a difficult position when interacting with agents whose role is not always clear.
On a different flight, a passenger who had made several trips to the bathroom was questioned by an air marshal and detained by the police after the plane landed.
"We have reached a point where you check in your civil liberties when you check in your bag," the traveler said, speaking anonymously because of the sensitivity of the situation. "It's a little over the top what's going on."
Customer complaints about the airlines' service and performance have risen. The Department of Transportation received 7,524 complaints about carriers in the United States in the first nine months of 2012, compared with 5,231 in the same period in 2011. Complaints about United topped the rankings, with 3,414 filed in the first three quarters, versus 1,132 for American Airlines, No. 2 on the list.
No federal regulation restricts what passengers can photograph or videotape on a plane, but Mr. Johnson said United published in its in-flight magazine a rule against photographing or recording aircraft equipment and airline personnel.
So where does that leave Mr. Pollock?
He said a United representative told him that their investigation indicated he refused to return to his seat, refused to stop taking pictures and refused to move away from the curtain when asked — all untrue, Mr. Pollock said.
"It's just emblematic of what air travel has become," he said. "If you ask a question on a plane, you're going to be identified as a problem and you're going to get whatever response they choose to take — and there's no recourse."
That feeling of "no recourse" has been heightened in the digital era, as customers are directed to Web sites to submit complaints and find it difficult to get more than a form response.
Jeremy Cooperstock, an engineering professor in Montreal, created the Web site Untied.com to help passengers in that bind. Besides collecting complaints about United — the site received 4,500 last year — Mr. Cooperstock lists contact information for United customer service managers and advises passengers, and airline employees, on their legal options.
United is suing him, seeking an injunction against disclosure of its managers' contact information.
"Passengers are increasingly dissatisfied with the service and treatment they receive," he said. "I feel the need to alert the public to their rights and help employees who have been victimized by their management."