IIRC Concorde was supposed to become a whole fleet of aircraft; however, due to fuel price increasing, demand was low, therefore, prices stayed high, therefore, demand stayed low, so the fleet idea had to be canned. Concorde would have been a great idea if the price had stayed low and they could have built the fleet that they intended to.
EDIT: To clarify the following article in brief, The plan was to have a supersonic air fleet "for the masses"; but, as prices to operate the planes became too high, and new regulations that ended up increasing the price even further were put into place, the only way to turn a profit was for companies to charge exorbitantly (~$10,000 one-way sometimes!); therefore limiting travel to the wealthy and keeping demand low -- thus, the death of the fleet. ~20 Condordes were built in total.
What are the reasons for the failure of Concorde? What improvements could be made to it?
- question from Harpeet
Your question is unclear as to whether you are asking why the Concorde failed to become a success in the first place or why the airlines decided to retire the plane in 2001. In any case, the reasons are largely similar.
The design of what ultimately became Concorde began in the late 1950s when commercial air service was just beginning to become the dominant form of long-distance travel. During the late 1950s and early 1960s, technology was progressing so rapidly that the public believed high speed aircraft and even commercial space travel would become commonplace in the near future. It was this mindset that made the Concorde possible, and it was shared by other nations as well. Both the Soviet Union and the United States were also developing their own equivalents to Concorde called the Tupolev Tu-144 and the Boeing SST.
Artist concept of the 1967 Boeing SST with variable-geometry wings
Unfortunately, the politics and economy of the world changed substantially between the early 1960s and the mid-1970s when Concorde was finally ready to enter service. One of the challenges that confronted Concorde was the growth of the environmental movement that bitterly fought against the plane. Chief among the complaints of environmentalists was the noise pollution that supersonic aircraft threatened to bring. It was because of this concern that most nations banned supersonic air travel over their territories to eliminate the danger of sonic booms. This legislation forced Concorde to seek out intercontinental routes across oceans. The routes that did travel over land, such as Washington DC to Dallas and London to Bahrain, were forced to remain subsonic and cruise at Mach 0.95. This cruise speed significantly increased fuel consumption and caused the cost per flight to skyrocket, which was one of the primary reaons why both routes were abandoned within a couple of years.
A second problem that plagued Concorde was the rise in oil prices that struck the West so forcefully during the 1970s. Supersonic flight requires powerful engines that consume much more fuel than traditional airliners flying at Mach 0.8. Oil was inexpensive in the early 1960s, so the airlines had little need to worry about fuel costs when the Concorde was being designed. As the airline industry changed in the 1970s and 1980s because of deregulation and increased competition, cutting costs became necessary simply for survival. Airlines just could not afford the cost of fuel needed for supersonic aircraft, so they had no interest in planes like Concorde.
Regardless, British Airways and Air France were able to overcome these challenges as best they could and eventually turned a profit on Concorde flights. They did so by abandoning the idea of supersonic travel for the masses and instead adopting a premium service catering to the elite. Concorde was most often flown by wealthy business executives and celebrities who needed to cross the Atlantic rapidly or who were simply attracted by the special treatment offered on Concorde flights. These upper class passengers could also afford to pay exorbidant ticket prices that could be as high as $10,000 one way. This business model allowed Concorde to generate a profit for its operators until the fleet was grounded following the Air France crash in 2000.
The accident investigation that followed lasted for an extended period and revealed a number of troubling safety concerns. Both British and French authorities revoked the Concorde's airworthiness certificates and mandated several modifications to the remaining fleet before Concorde would be allowed to fly again. Both airlines felt the aircraft could still be profitable and invested millions of dollars to return Concorde to service. Once authorities had agreed that the plane was again safe to fly, passenger service resumed in September 2001.
By this time, however, the air travel industry was in a serious downturn following the September 11 terrorist attacks. The slump in business caused passenger traffic on Concorde to drop so low that the airlines were having difficulty turning a profit. The situation only became worse when Airbus, the maintenance and parts supplier for Concorde, announced that the aircraft would no longer be supported after October 2003. The loss of this support meant that the airlines would be forced to acquire all the spare parts and complete all maintenance on their own, which was simply too expensive. The Airbus decision to stop supporting Concorde coupled with the loss of passengers doomed the aircraft to retirement. As the chief executive of Airbus, Noel Forgeard, said, "The costs of operating Concorde, and in particular maintenance and support, have become such that operations are unrealistic for any operator."
As for the second part of your question, there are a number of improvements that could potentially make supersonic travel more economical. One of the most important concerns to airlines is the cost of operating an aircraft per the number of passengers it carries per mile it travels, or the "cost per seat-mile." Concorde never proved to be a commercial success because it cost too much to operate and carried too few passengers. To be a success, any future SST will need to carry at least twice as many passengers as Concorde and its fuel consumption will have to be comparable to a competing subsonic airliner.