The subtle and graceful external shape of Concorde hides a great many advanced engineering features. The wing is a masterpiece of aerodynamic shaping. The slender delta shape with an ogival (curved) leading edge was only arrived at after a huge amount of wind tunnel testing and reaches optimum efficiency at around Mach 2.2. Most of the fuel is stored in the wings, where it acts as a heat sink for the wing skin during prolonged supersonic flight. Fuel is also used to control the aircraft centre of gravity, to counter-act the rearward shift in the centre of lift as the aircraft goes supersonic. Fuel is pumped into trim tanks in the rear fuselage during acceleration and forward again during deceleration to subsonic speed. Computer controlled variable-area air intakes ensure that each engine receives an optimum air flow under all flight conditions. The nose of the aircraft can be hinged down 17.5 degrees to improve the view of the pilot while landing or taking-off, although in practice only 12.5 degrees is normally used.
On 10 April 2003, British Airways and Air France simultaneously announced that they would be withdrawing Concorde from service. Since it's return to service, passenger numbers had not recovered to a sustainable level and the aircraft could no longer made a profit. The drastic decline in transatlantic air travel - Concorde's only route - after September 2001 has meant falling passenger revenue at the same time as support costs had increased. For example, the mandatory fitting of new cockpit security doors will cost ten times as much for the small Concorde fleet as it will for a Boeing aircraft. Since another operator could not be found, the aircraft will cease operations at the end of October 2003 and the airframes placed with museums.
In the end, the real legacy of the Concorde program is not just a beautiful airliner, but the culture and infrastructure of European technical collaboration which arose from its production. The Concorde factories at Filton and Toulouse became part of the Airbus company, which has now reached parity in airliner sales with the once dominant Boeing. Meanwhile, (at least until October), Concorde is still the world's only commercial supersonic airliner in service.