From the perspective of the aviation industry, there have been some encouraging developments on the issue of Deep Vein Thrombosis (DVT).  DVT is a condition that can develop on long-haul flights when a blood clot forms in a deep vein (typically the leg).  If this clot later breaks loose and lodges in the brain, heart, or lungs, it can be life-threatening.   
Recent court decisions held that an airplane manufacturer and several airlines were not liable for DVT related injuries.  
In In re Deep Vein Thrombosis, 2005 WL 1422399, the US District Court for the Northern District of California held that an airplane manufacturer had no duty to design a seat tracking systems to prevent allegedly unsafe seat configurations.  Boeing, an aircraft manufacturer, sold several completed aircraft to various airlines.  Several passengers who suffered from DVT after long-haul flights brought actions against Boeing.  
Plaintiffs contended that the manufacturer should be held liable for selling the completed aircraft, the seat configuration of which allegedly promoted DVT.   The court, however, ruled that the plaintiffs had a “marred concept of ‘completed product’” and held for Boeing.  Boeing sold a completed product consisting of an aircraft without the seats.[1]  The manufacturer thus could not be held liable for a defective product that it had not manufactured.  Furthermore, Boeing was without legal authority to require the use of certain seat tracking systems in its aircraft because such authority was vested in the Federal Aviation Administration (FAA).  
Another court recently held that the failure of airlines to warn passengers of the risk of developing DVT on flights did not constitute an “accident” as defined by the Warsaw Convention.  Baxley v. Delta Airlines, Inc., 4:04CV1600 (6th Cir. 2005).  C.f. Rodriguez v. Ansett Australia, 383 F.3d 914 (9th Cir. 2004); Blansett v. Continental Airlines, Inc., 379 F.3d 177 (5th Cir.), cert. denied, 125 S. Ct. 672 (2004).  
In Baxley, plaintiff relied on Olympic Airways v. Husain, 540 U.S. 644 (2004), in which the U.S. Supreme Court held that an injury need not be caused by a single event constituting the “accident,” rather, the plaintiff need only prove that “some link in the chain [of events] was an unusual or unexpected event external to the passenger.” Id. (refusal to aid an ailing passenger constituted an unusual and unexpected event when contrary to airline policy).  The court, however, noted that the FAA does not require DVT warnings.  The failure to provide such a warning and the resulting DVT, therefore, could not be classified as unexpected and unusual because the “mere occurrence of DVT does not constitute an ‘accident’ when the injury occurs on an aircraft that operates in the ‘usual, normal, and expected’ manner.” C.f. Rodriguez, 383 F.3d at 917 (alleged failure to warn passengers of risk of developing DVT during long flights is not an “accident” absent evidence of industry standard or airline policy requiring warning and showing that airline’s conduct was an unexpected and unusual event external to the passenger).
The court in Mienin v. Midwest Express Airline, 2005 WL 1208507 (Wis. App. 2005), held that federal law preempts any state requirement for DVT warnings because Congress has granted the FAA the authority to establish complete and thorough safety standards for air transportation.   Permitting state-imposed restrictions would overextend state authority and lead to inconsistency.

Commentary: It is a fairly well established principal of tort law that one who assumes a duty to another has a duty to perform that duty non-negligently.  Similarly, the standard of negligent conduct is not static; it changes with the state of scientific knowledge.  These principles could potentially impact both the happening of an “accident” under the Warsaw regime and a potential negligence claim in the non-Warsaw context.  For example, in a classic two-edged sword, the airline that adopts a standard practice for issuing DVT warnings and recommendations, exposes itself to liability for an “accident” or negligence should it deviate from the standard.  On a related note, if the body of scientific knowledge on DVT were to suggest that failure to adopt such procedures and warnings poses an inherent risk, omitting such procedures could evolve into another potential exposure.
Certainly, a cogent argument could be made at this time that, on all but the longest flights, the risks presented by encouraging passengers to wander about the cabin outweigh those posed by DVT.  At which point the DVT risk outweighs the risk of “wandering” is best left to future study and will itself invariably depend upon the medical condition and predisposition of the individual passenger.  Thus, while the above results are encouraging, they will not be the last word in this developing area as both industry procedures and the scientific foundations of DVT continue to evolve.
[1] Boeing maintained that in most cases it sold the aircraft without installing seating. In a few cases, however, it installed seating only after the airline purchased seats and requested installation in accordance with FAA-approved configurations.