Not so long ago, a man on an airplane was served a sandwich he didn't like. He used Twitter -- the real-time personal news feed, if you didn't know -- to alert the world to his displeasure. An airline employee on the ground saw the tweet, relayed the message to a flight attendant who minutes later asked the man what could be done to assuage his disappointment.

Welcome to travel 2012 style, if you're doing it right.

Once seemingly impenetrable behemoths, airlines have become remarkably accessible thanks to social media, especially in the real-time world of Twitter. Most, if not all, airlines have Twitter feeds that allow customers to converse and, more important, solve problems in real time, whether for a large issue (stranded in an airport) or small (a lousy sandwich).

Stuart Greif, vice president of global travel for J.D. Power and Associates, said the sandwich story, which he said he discussed with an executive of the airline involved, shows social media's benefits for the travelers who are savvy enough to use them. "If a customer has a problem, the fastest way to address it has become social media," Greif said. "Younger generations might never call into a call center. They might always go online and address these things in real time."

Go to any of the major airlines' Twitter feeds, and you will see (often entertaining) exchanges with frustrated passengers.

"We consider Twitter the canary in the coal mine," said Morgan Johnston, JetBlue's social media strategist. "It's not always fun to be called out publicly, but if there's something really wrong with our operation, it shows up a lot faster, and we're able to fix it."

Among the more aggressive Twitter users has been American Airlines, which has sent more messages than any of its competitors and which recently expanded its Twitter coverage from 6 a.m. to midnight, up from 7 a.m. to 8 p.m. The ultimate goal is staffing 24 hours a day, as several other airlines do.

Why does Twitter mandate such attention from the airlines? Its public nature, of course.

"It is public -- very public -- especially those who tweet us who have large followings and a big sphere of influence," said Annette Hernandez, who manages American's social media customer service. "We want to be right on target when we respond. Who knows who will see it?"

Brian Conway, one of American Airlines' two original tweeters on behalf of the public relations firm Weber Shandwick, called tweeting on behalf of an airline a "very heavy responsibility."

"You have to double- and triple-check everything you write and think, 'How do I want the customer to feel when I post this?'" he said.

Advantage, airline customer. At last.