<P> Airliner cabins were usually maintained at a pressure equivalent to 6,000--8,000 feet (1,800--2,400 m) elevation . Concorde's pressurisation was set to an altitude at the lower end of this range, 6,000 feet (1,800 m). Concorde's maximum cruising altitude was 60,000 feet (18,000 m); subsonic airliners typically cruise below 40,000 feet (12,000 m). </P> <P> A sudden reduction in cabin pressure is hazardous to all passengers and crew . Above 50,000 feet (15,000 m), a sudden cabin depressurisation would leave a "time of useful consciousness" up to 10--15 seconds for a conditioned athlete . At Concorde's altitude, the air density is very low; a breach of cabin integrity would result in a loss of pressure severe enough so that the plastic emergency oxygen masks installed on other passenger jets would not be effective and passengers would soon suffer from hypoxia despite quickly donning them . Concorde was equipped with smaller windows to reduce the rate of loss in the event of a breach, a reserve air supply system to augment cabin air pressure, and a rapid descent procedure to bring the aircraft to a safe altitude . The FAA enforces minimum emergency descent rates for aircraft and noting Concorde's higher operating altitude, concluded that the best response to pressure loss would be a rapid descent . Continuous positive airway pressure would have delivered pressurised oxygen directly to the pilots through masks . </P> <P> While subsonic commercial jets took eight hours to fly from New York to Paris, the average supersonic flight time on the transatlantic routes was just under 3.5 hours . Concorde had a maximum cruise altitude of 18,300 metres (60,039 ft) and an average cruise speed of Mach 2.02, about 1155 knots (2140 km / h or 1334 mph), more than twice the speed of conventional aircraft . </P> <P> With no other civil traffic operating at its cruising altitude of about 56,000 ft (17,000 m), Concorde had exclusive use of dedicated oceanic airways, or "tracks", separate from the North Atlantic Tracks, the routes used by other aircraft to cross the Atlantic . Due to the significantly less variable nature of high altitude winds compared to those at standard cruising altitudes, these dedicated SST tracks had fixed co-ordinates, unlike the standard routes at lower altitudes, whose co-ordinates are replotted twice daily based on forecast weather patterns (jetstreams). Concorde would also be cleared in a 15,000 - foot (4,600 m) block, allowing for a slow climb from 45,000 to 60,000 ft (18,000 m) during the oceanic crossing as the fuel load gradually decreased . In regular service, Concorde employed an efficient cruise - climb flight profile following take - off . </P>

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