You are right, one should never under estimate the danger, but I wonder what the exact reason for his DVT was? I was an airline pilot for over 30 years and suffered twice in the last 10 years from a DVT. Fortunately I was referred to a top man at the local University Hospital. He discovered I suffered from a gene defect known as Factor V Leiden. This meant that I was susceptible to clotting. After the first DVT I was allowed back to flying but had to inject myself with an anti-clotting agent (lasted about 24 hours) before each flight. The second DVT occurred while on leave and being hit on the leg with a heavy wooden shelf. The resulting trauma caused a clot and that was the end of my flying career. Too many people, both aircrew and passengers, are unaware of this condition and others of a similar nature and the press with its banner headlines about "Economy Syndrome" have not helped. Especially passengers are wont to think it is flying that causes a DVT. This is probably the result , the cause being perhaps a medical condition they themselves are carrying.