Potentially fatal formation of blood clot within a deep vein, usually in the lower limbs. Limited movement in cramped conditions, e.g. long haul flight conditions, appear to be the main cause. Air passengers making personal injury claims have to overcome the Warsaw Convention that limits compensation to ‘accidents. There is no definitive answer in English law as to whether DVT is caused by an ‘accident’. Adopting the approach in Air France v. Saks (1985), a US case, a High Court decision (2002) held DVT not to be an accident for the purpose of the Convention.