BANKRUPTCY has become a familiar destination of U.S. carriers, and now it is Pan Am's turn. Time was when this kind of announcement would chill passenger traffic, but today several airlines continue to operate as they scratch for survival by distancing themselves with Chapter 11 from the claims of creditors. Now almost cashless, Pan Am is the third of the nine largest United States carriers to seek this protection in the past two years. Continental, fifth largest, filed last month, and Eastern did it in March of 1989. Both are still flying, sort of, and Pan Am expects to continue in some pared version.

Founded 63 years ago by an Army captain to haul mail between Key West and Havana, Pan Am merged, grew and prospered in the days of tight regulation. With a near monopoly on international air travel and solid contacts in Congress, the airline pioneered routes around the globe and became the country's flagship carrier. As it was supposed to, deregulation of the industry in 1978 brought competition. Some competitors acquired newer aircraft; Pan Am continued to fly its older gas guzzlers. In the 1980s Pan Am began selling off assets to cover deficits.

As an airline concentrated on international routes, Pan Am was hit hard by the wave of terrorist attacks that discouraged travel abroad. In 1988 a bomb destroyed a Pan Am jumbo jet over Lockerbie, Scotland, killing 270 people and costing the airline an estimated quarter of a billion dollars in bookings in the following year. Top this with a recession and the huge increases in fuel costs since the Persian Gulf crisis, and Pan Am took on red ink by the ton.

Chapter 11 protection became essential if Pan Am was to avoid liquidation and obtain $150 million from United Airlines and the Bankers Trust Co. as a loan against a $400 million sale of its London routes to United. This has won approval of a bankruptcy court but still needs approval of the British government. The U.S. Department of Transportation has tentatively approved the sales of international routes by Pan Am and TWA.

If all of this comes together, Pan Am will use its new money to expand service to Eastern Europe and the Soviet Union while continuing profitable Latin American routes. Perhaps Pan Am will find the going greater than it's been of late. After all, nearly 20 percent of the U.S. airline capacity these days is owned by carriers in Chapter 11. Foreign investments in the U.S. industry -- a delicate policy area -- are likely to come under increasing review in the search for solvency in the skies.