Here is a link to an article published by the Aerospace Medical Association...
"TRAVELLER’S THROMBOSIS
Review of Deep Vein Thrombosis associated with Travel
April 2001
Introduction
Deep vein (or venous) thrombosis is a condition in which a small blood clot (thrombus) or clots (thrombi) develop(s) in the deep veins usually of the leg. The condition itself is not dangerous, but the complication of pulmonary embolism (venous thromboembolism – VTE) can of course be life threatening.
There is increasing suspicion amongst the travelling public and the international media of an association between the occurrence of deep vein thrombosis (DVT) and air travel, but so far there is only circumstantial rather than epidemiological evidence in support of this (Ref 18). It has been reported (personal communication) that a number of international airlines are receiving writs from lawyers representing passengers who have suffered DVT in flight.
This paper by the Air Transport Medicine Committee of the Aerospace Medical Association provides an overview of current scientific evidence."
Full text:
Traveller's Thrombosis