Researchers suspect that the so-called "economy class syndrome" may kill thousands of air travelers each year. Economy class syndrome is characterized by the formation of a blood clot during long-haul airline flights. Researchers say that extended periods of inactivity, such as inactivity experienced on long flights, may trigger the deadly blot clots. Ashford hospital in London reports that at least one patient each month dies at the hospital from economy class syndrome. The hospital is located close to London's Heathrow airport.

Many airlines, including international carrier British Airways, are beginning to warn passengers of the danger of economy class syndrome, also known as deep vein thrombosis. Critics contend that the airlines' warnings are too little, too late. Many believe that the airlines have been aware of the problem for some time, yet have refused to disclose the risk to the flying public. "These are people who die as they get off the aircraft. Around one million people come into Heathrow on long haul flights each month so it may not seem much compared to crossing the road. But it is something that airlines can help prevent." Said John Belstead, spokesman for London's Ashford hospital.

The economy class syndrome may be a misnomer as the fatal blood clots can affect those who sit motionless for long periods of time, no matter the level of fare service. Passengers on long-haul flights are now being advised to drink plenty of water, partake in mild exercise and avoid alcohol. The blood clot associated with economy class syndrome usually occur in the legs, but can move to the lungs where they are almost always fatal. The syndrome was first brought to light in Australia. Over 800 Australians are suing several airlines over injuries and deaths caused by economy class syndrome.

Researchers, while alarmed at the apparent number of victims of economy class syndrome, are nevertheless unsure of its threat, as most hospitals have not kept records regarding the circumstances surrounding blood clot related illnesses. "Doctors have never even thought to ask whether a blood clot victim recently completed a long flight," said Bill Hansol, spokesman for the Tracing Group, an airline consulting organization.