Images of bikini-clad women in Thailand posing suggestively in an online ad for a local airline inflamed passions -- both positive and negative -- earlier this year.

Domestic low-cost carrier Nok Air stood at the center of the frenzy. The airline had employed the provocatively clothed women to attract more attention in a Facebook publicity move.

It worked.

"I kind of expected it to be fairly controversial, but at the end of the day more people ended up liking it than hating it," says Patee Sarasin, Nok Air's chief executive officer.

"When it debuted on Facebook, we had over 200,000 likes. I'm happy."

Thailand-based low-cost carrier Nok Air's controversial calendar. Nok Air

The campaign proved to be a social media success -- it also brought into focus the different ways international airlines use the attractiveness of cabin crews to brand and market their product.

Though acknowledging that "beautiful does not equate to being a good flight attendant," Ji Yang Xiong, director of China's Foreign Airlines Service Corporation, notes a difference in aesthetics when comparing airlines from the East and West.

"Maybe Asian airlines emphasize looks just a bit more when compared to European or Middle Eastern airlines," says Xiong. "European airlines don't have any requirement on looks. They mostly focus on personality and having the right attitude for the job and a service-oriented mindset."

Legal issues: Grounded at 30?

While some Asia-based airlines openly embrace glamour in the cabin, most U.S. and European airlines long ago altered such strategies to reflect shifting social standards and more severe legal restrictions.

"It's one thing to be able to help people out of an emergency exit door, it's another to say they must weigh less than 130 pounds, as Pan Am and others might have done in times gone by," says Kenneth Quinn, partner and head of aviation practice at the Washington, D.C.-based law firm Pillsbury Winthrop.

"Most governments have enacted laws and other protective measures against gender and age discrimination, as well as fitness discrimination," says Quinn. "But Asian countries have less precise formulas in their labor laws that permit airlines to impose age and appearance limitations upon flight crews."

In addition, says Quinn, governmental bodies in Asia are generally less committed to regulatory oversight in this area.

"They try to leave it to the airlines and unions and work forces to deal with any problems," he says. "Certainly weight and appearance limitations tend to be not strictly enforced."

"Laws covering employment and particularly discrimination tend to be less rigid in Asia," agrees Tom Ballantyne, aviation expert and chief correspondent for Hong Kong-based "Orient Aviation" magazine.

"A British Airways or a Qantas in Western society would never get away with promoting the sort of image that, for instance, Singapore has always done with its Singapore Girls."

Nok Air has no flight attendants over the age of 30, says CEO Sarasin. While laws in the West protect against discrimination, "it is kosher here in Asia to push youth and beauty," he says.

The lifespan of a Nok Air flight attendant is short, according to Sarasin.

They typically take to the skies from graduation around the age of 23, stay in the company for three years -- maybe another two if they're "really, really good" -- then can move to non-cabin crew departments or get help with being placed with other airlines.

"We keep them young -- not because we're sexist -- but because our customers prefer younger crews," says Sarasin. While "everyone is unionized in the United States, we are much more open. That's what gives Asia the magic. We've been radical from day one, differentiating our marketing. If we don't, we die."

Profits: No link between beauty, bottom line?

The jury is still out on whether sex sells more seats.

"I've never seen any evidence that directly links the beauty of flight attendants to the bottom line," says Ballantyne. "Certainly it is true that many airlines in Asia-Pacific, especially low-cost operators, base part of their brand image on young, attractive flight attendants. How that translates to additional passenger numbers I'm not sure."

"I'd say it's impossible to put a monetary value to the contribution of the Singapore Girl to Singapore Airlines' success over the years," agrees Nicholas Ionides, spokesman for legacy carrier Singapore Airlines, referring to the well known imagery of the company's female flight attendants -- conceived in 1972 -- wearing distinctive "sarong kabaya" uniforms.

Nok Air's Sarasin himself hedges on whether his company's Facebook stunt helped pull in more profits.

"It's hard to measure if it boosts sales or not," he says. "Load factor (the number of seats sold for flights) has always been in the 80 to 90 % range. But it did bring Nok Air into the limelight in terms of brand awareness."

If anything, the charismatic CEO believes the added publicity brought a change to the passenger mix.

Before the photo shoot, international travelers made up 10 percent of the passenger manifest. After the shoot, the percentage jumped to 18 percent based on passport checks.

With Nok Air set to make its first international flight -- to Yangon, Myanmar, in the third quarter of 2013 -- Sarasin says: "It's good timing."

Offensive: Is "sexy" a bad word?

Thailand's Ministry of Culture received complaints from local organizations and critics who were shocked by Nok Air's sexy photo shoot, according to local Thai media.

One fear was that the photo shoot might propagate Thailand's image as a destination for sex travel -- but the Ministry of Culture says no laws were broken.

"The Ministry of Culture didn't call me. In fact, I received no call from any government agency," points out Sarasin. "We were all careful not to expose the women to be too naked."

Contacted by CNN, the Ministry of Culture says it's no longer commenting on the matter.

While sex appeal is the blatant strategy for Thailand's Nok Air, further north "sexy" is a bad word in the Korean airline industry -- which is not the same as saying that Korean carriers don't value what might politely be called "attractiveness."

At ANC flight attendant academy in Seoul, students practice role-playing in a classroom simuating a plane. courtesy ANC

"Projecting any sort of sexy image in a flight attendant interview would be hugely risky here," says Mi-kyung Chung, a former flight attendant who now teaches at the Airline News Center (ANC) flight attendant academy in Gangnam, Seoul.

This might come as news to flight attendants on South Korea's Asiana Airlines, whose union has been in a long-running conversation with the airline about ending its skirts-only dress code and relaxing strict guidelines for hairstyles and makeup. In February, the airline said it would adopt a trousers option on its next uniform renewal.

With a "few thousand students" -- mostly women -- ANC is considered the largest flight attendant academy in the country. The school charges $1,440 for an all-inclusive package in which students can take classes for as many months -- or years -- as they need.

Despite Korean Air's obvious use of old fashioned sex appeal in its widely distributed "For life on a whole new scale" series of advertisements , professionals insist that sex isn't the primary appeal.

Instead of sexy, "bright, clean and sophisticated" is the look that's most sought after in the recruitment process for Korean airlines, according to Jinah Lee, a flight attendant turned ANC lecturer.

Korean airlines have been setting the standard for flight attendants for almost a decade now, says Eunice Kim, head of BCCA flight attendant academy in Shinchon, South Korea, which specializes in foreign airline recruitment.

She admits that looks are part of the package.

"Recruiters for the foreign airlines I work with often tell me that Korean flight attendants are much more good looking and better to work with compared to flight attendants from other countries," says Kim.

She says the BCCA's 2,200 students include many foreign-educated young women, "NYU grads," PhDs and graduates from the top universities in Korea.

According to Kim, a number of foreign students come to South Korea to study at the academy. Some, she says, even undergo cosmetic surgery during their stay in the hopes of being recruited by foreign airlines.

When asked about the demand for Korean flight attendants at foreign airlines, Kim cites "high education rates ... good teeth, complexion, height and positive outlook" as attributes.

Students at Seoul flight attendant academies practice getting the right look. courtesy ANC

In addition, Korean flight attendants embrace the service mentality more completely, says the BCCA head.

"Personally, I think it comes from the conservative Confucian background, where women were expected to do a lot of the service in the household," says Kim.

Attitude trumps looks

Chinese flight attendant hopefuls at an interview for China Southern airlines in Beijing. str/afp/getty images

The sentiment is similar in China, where the Foreign Airlines Service Corporation (FASCO) recruits Chinese flight attendants for foreign airlines, such as Emirates Airlines and Qatar Airways.

At the end of 2012, FASCO helped about 1,200 Chinese nationals find flight attendant jobs around the world, according to director Ji Yang Xiong. In 1996, when the company first began recruitment services, just "a few hundred" candidates applied.

While airplane safety, meal service and customer hospitality are taught, physical fitness is also emphasized.

"Aerobics classes are held in both aviation schools and in training centers in order to keep the aspiring flight attendants in shape, to refine their figure and posture and to strengthen their body," says Xiong.

Some candidates even learn kung-fu and yoga "so that they are ready to face stressful situations."

Training and attitude might well go farther than a mere attractive image in explaining the success earned by Asian flight attendants.

"American service standards generally have dropped vastly below Asian service standards in many industries, and most particularly in hotel and leisure and travel communities," says aviation law expert and frequent traveler Quinn.

This may seem self evident to certain frequent fliers, says Quinn, but for those flying on an Asian carrier for the first time, the difference can be a surprise.

"What tends to be lost in the debate over this is that it's not a crime to insist upon high standards of service and courtesy and professionalism in flight crews," says Quinn. "For the U.S. businessperson who spends a lot of time in Asia -- I'm just back from Tokyo this week -- the contrast between U.S. service standards and Asian carrier service standards could not be more stark.

"It's a quantum leap in service standards as soon as you hit Tokyo and go beyond, whether you're on a Japanese carrier or Singapore Airlines or an airline from Hong Kong or Thailand. They're all vastly superior in the service level.