Shares of AMR Corp. (NYSE: AMR), the parent corporation of American Airlines, have plunged to their lowest levels on fears the company may have to file for bankruptcy protection.

As of 2:38 p.m. (New York Time), AMR shares are down 31.1 percent to trade at $2.03 per share – a level they has not seen since early 2009.

The stock has not closed below $2 since 2003.

Year to date in 2011, AMR shares have plummeted more than 60 percent.

According to reports, American Airlines, the third biggest carrier in the U.S., is in a highly vulnerable financial position – among other things, its labor And financing expenses are higher than those of its carrier peers. The airline is also losing money this year, which would make it the fourth consecutive year of posting a loss.

Ray Neidl, an analyst for Maxim Group LLC in New York, told Bloomberg: “The odds are better than 50-50 that we’re going into a recession. If that’s the case, you’re going to start seeing some softness in demand come October, in the fourth quarter and next year.”

According to reports, American Airlines is also vulnerable to higher fuel costs since it relies on an aging, less fuel-efficient fleet of carriers.

Andy Backover, a spokesman for American Airlines, told media that bankruptcy is certainly not our goal or our preference. We know we need to improve our results, and we have a sense of urgency as we work to achieve that.”

Meanwhile, a wave of sudden retirements by American Airlines pilots is adding to the company’s woes as workers attempt to protect their pensions ahead of a potential bankruptcy filing.

Ironically, because American Airlines was one of the very few major carriers not to file for bankruptcy over the past decade, it has had to retain its pension obligations and retiree benefits.

According to Barron’s, Neidl said: “We are in a down market today but the exceptional number of American pilots retiring is a sign that they want to protect their pensions and get out before a possible filing further depressing the stock price.”

In August, 111 pilots retired while another 129 called it quits in September. (According to reports, only about a dozen American Airlines pilots retire each month).