How do airline stocks react to airline crashes? It s not what you might think.

On Friday, stock traders sent shares of US Airways up 13 percent. The gains followed Thursday s dramatic crash landing of the airline s flight 1549 on the Hudson River, which was survived by all 155 people on board. But would US Airways (LCC) shares have been decimated had flight 1549 not been so fortunate?

Often it s the not the crash itself that determines what happens to the stock, but what caused the crash. Only two major accidents involving U.S. air carriers have seriously affected an airline s stock over the short or long-term, says Bob McAdoo, senior research analyst for airlines at investment bank Avondale Partners.

As long as the airline is not primarily at fault for the disaster, investors typically shrug it off. The stocks of both American Airlines and United Airlines fell after their airplanes were involved in the Sept. 11 attacks, but so did the shares of all airlines. McAdoo says even the US Airways share price rally Friday should be taken with a grain of salt--many airline stocks were up because the price of oil fell.

In the case of the two major accidents where the airlines shares were affected, though, the stocks were crushed. The first involved Air Florida Flight 90 crashing into a bridge straddling the Potomac River in Washington D.C. in Jan. 1982. The crash was later attributed to probable pilot error. Before the crash, Air Florida s stock was as high as $17.50. It was barely $2 by Nov. 1982 and the carrier went bankrupt in June 1984.

The second: the crash of ValuJet Flight 592 in the Florida Everglades in May 1996, which killed all 110 aboard. ValuJet already had a poor safety record, and its stock fell 23 percent the first day after the crash (shares of Delta, ValuJet s chief rival, rose that day). The airline was found at partial fault for the crash and was grounded in June 1996. ValuJet eventually merged with AirTran and dropped the ValuJet name.

Crashes, when they aren t the fault of the airline, don t make a big dent in airline s short-term finances, either. The airplanes are often insured for more than they are worth. Airlines actually make a little money on the insurance claim, McAdoo says.

Below, a look at how some airline stocks have fared following a crash involving the carrier:

*American Airlines crash in Chicago, May 25, 1979. 273 killed.
One trading day after the crash the stock was down 3.2%
One month the stock was up 25.9%

*TWA crash off East Moriches, New York, July 17, 1996. 230 killed.
One trading day after the crash the stock was down -8.9%
One month later the stock was still down -8.9%

*ValuJet crash in Florida Everglades May 11, 1996. 110 killed.
One trading day after the crash the stock was down 23%.
One month later the stock was down 58.3%