Airlines put fliers in the seat of danger, new litigation claims.

Something's up in aviation law: Recent lawsuits seek to hold airlines responsible for blood-clot-related injuries and deaths brought on by air travel. The cases allege that airlines have been negligent in failing to advise passengers to flex their leg muscles during long flights to prevent blood from clotting in the lower legs, a condition that can lead to pain, fainting, and even death.

A class action suit is under way in Australia, but only a handful of cases have been filed in the United States. "This is a new area of liability for air carriers," said plaintiff attorney Daniel Rose of New York City. "Plaintiff firms don't want to rush into these cases. We want to approach them properly and thoroughly."

The condition, deep vein thrombosis (DVT), occurs when blood clots form in the calves. As a clot grows, it casts off smaller clots that can move to the heart and into the arteries of the lungs, blocking blood flow and depriving the body of oxygen. In rare instances, the clot travels toward the brain, causing a stroke. People who survive may face lifelong health problems.

Airline passengers are especially at risk because high altitudes increase blood's coagulability, slowing blood flow and causing it to pool in the lower legs. Immobility, cramped seating, compression of the thighs on a seat edge, and dehydration due to cabins' low humidity levels contribute to the pooling and clotting.

Although the condition can strike otherwise healthy passengers--1 in 10 suffers symptomless DVT, according to a study in the medical journal TheLancet (May 12, 2001)--certain ones are at greater risk. They include those with heart disease, cancer, and a history of blood clots; those who are pregnant or use oral contraceptives or hormone replacement therapy; and those who have had recent surgery or leg injuries.

Most of the DVT lawsuits claim that airlines are aware of the condition and its danger but do not alert passengers sufficiently. Some encourage passengers to move about during a flight but do not say why. To claim negligence, plaintiffs need to show that the airline is responsible for passengers' welfare as well as for their safety, that it violated that duty, and that DVT occurred as a direct result. But under Warsaw Convention protocols, airlines are responsible only for passengers' safety, not their health.

How can plaintiffs overcome the protocals? Rose said, "At a certain point it becomes a spillover effect: If an airline is aware of a condition that threatens passengers' health, it becomes a safety issue."

In the United States, lawyers are in a holding pattern until researchers establish a definitive link between air travel and DVT. Scientists and airline industry representatives who met at a World Health Organization conference in Geneva, Switzerland, in March determined that a link probably exists but more evidence is needed.