Indignant letters, e-mails and phone calls can still get results for unhappy airline travelers, but more are finding that if you really want to vent your frustrations, you can now be loud and fast and public.

At least that's the buzz on Twitter, where airlines are discovering that fuming passengers who have been stranded, delayed or just plain piqued are increasingly letting their undiluted rage fly around the Internet, often from the confines of their cramped airplane seat.

Twitter and other fast-growing social networking websites like Facebook and YouTube have sprung up as yet another front in beleaguered airlines public relations battle.

Although such sites have practical uses for airlines -- say, publicizing fare sales and flight information -- experts said the technology has put carriers on the defensive as they race to tame Twitter furies every day.

It's almost an underground rage factory, said Terry Trippler, at tripplersview.com, a travel opinion website. Rarely, I see Twitter messages praising an airline. It's usually attacking an airline.

Twitter, which lets people broadcast 140-character instant text messages to countless readers, has quickly been embraced as a powerful tool to counter censorship. Twitter messages, or tweets, from Iranian protesters after the recent disputed elections became a running part of the drama.

On last Wednesday morning, Twitter's featured posts about airlines included the following:

Screw american airlines. Every plane has Been broken. Gah. So done, read one post from Twitter user sheissilenttoo.

Shame on you Continental Airlines, read another post from user DiscoverU.

United airlines, you are the bane of my existence, user elnodonle wrote.

Continental Airlines and AMR Corp's American Airlines declined to comment specifically on those posts. A United Airlines spokeswoman was not immediately available to comment.

We are monitoring tweets and are responding directly or publicly where appropriate, said Continental spokeswoman Kelly Cripe.

Billy Sanez, who manages social media for AMR, said social media enable better dialogue with customers.

Twitter and a lot of the other social media sites and tools are a way for people to create a conversation or say something, he said. If they want to chat and if they want to have a conversation, we'll have a conversation. If they want to say something they have an opportunity to express it.

ONE MORE HEADACHE?

For overcrowded U.S. airlines, battered by volatile fuel costs and economic recession and labor unrest, bad publicity has become a part of daily operations. But air carriers can ill-afford to lose the loyalty of their customers.

Airline industry issues seem to be more visceral. People can resonate immediately with them, said Kevin Mitchell, head of the Business Travel Coalition, which represents business travelers. Where there are options, it means booking away.

That's why satisfying customers is more important than ever for airlines.

In the last year, U.S. airlines slashed the number of flights to control costs. Planes remain packed: load factors, measuring how full a plane is, were near 85 percent for the top nine U.S. airlines in July.

Despite the crowded planes, on-time performance has improved. U.S. Transportation Department data for first-half 2009 show 78.9 percent of flights landed within 15 minutes their scheduled arrival. In 2000, that was at 72.6 percent.

So by that measure, air travelers should have less to complain about these days. But don't tell that to airlines.

A lot of people are upset, and they use these channels to vent, said Christi Day at Southwest Airlines, who runs the carrier's Twitter and Facebook profiles. The main thing that our customers need to know is that we hear them.

But it's not just the flood of irate Twitter postings that can give an airline new bumps in their ride.

Earlier this year, a Canadian musician recorded a song and video called United Breaks Guitars after he said United Airlines failed to take responsibility for damaging his instrument during a flight.

The video, which was posted on Google Inc's YouTube, became an Internet hit. United quickly apologized and made a contribution to a music charity in the man's name.

Kate Hanni, founder of FlyersRights.org, and a vocal airlines critic, said social networking has given voice to travelers who otherwise would have fumed in silence.

It creates an awareness for people that these things are happening all the time, Hanni said.

FlyerRights.org has lobbied Congress for legislation on passenger rights, spurred by well-publicized incidents that left passengers stranded on planes for many hours.

When I hear about a stranding event where someone is stranded right then, I tweet it, Hanni said.

(Editing by Robert MacMillan and Philip Barbara)

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