High-Speed Transport in Commercial Aviation

By Asif Siddiqi, U.S. Centennial of Flight Commission

The post-World War II boom in commercial aviation pointed the way to faster and larger passenger aircraft for passengers. The most talked about frontier was the sound barrier. Various experimental and military jets had paved the way in the late 1940s and 1950s. The first concrete steps towards supersonic passenger aviation had been taken by the French and the British, who had combined resources to create the Concorde, a high-performance passenger jet capable of flying at more than twice the speed of sound. After a long development period lasting nearly 15 years and involving large amounts of government support, the British Overseas Aircraft Corporation (BOAC) and Air France began flying the aircraft in the early 1970s. The first flights into the United States began in May 1976 into Washington, D.C.'s Dulles Airport. No U.S.-owned airlines ever purchased the Concorde, convinced that existing subsonic jets were more economical. In the 1970s, the Soviet Union also introduced its own supersonic passenger aircraft, the Tu-144. The project, however, did not fare well due to a variety of technical and financial problems.

On the American side, the search for a supersonic transport (SST) proved to be a long and elusive journey. After a number of interagency studies, President John F. Kennedy, in June 1963, called for the development of a commercially successful SST. At the time, planners believed that the SST would be able to fly at Mach 3, i.e., much faster than the Concorde. The Federal Aviation Agency (FAA), an executive agency that reported directly to the president, pushed strongly for SST development under its head Najeeb Halaby, a former test pilot. The U.S. government undertook to finance the major portion of SST development costs. Despite optimistic forecasts, the SST program suffered through a number of managerial debacles through the 1960s. After several reviews, Halaby ceded control of the program to then-Defense Secretary Robert McNamara. They each had very different views on how to proceed with SST development. Halaby preferred to iron out technical problems as they faced them, while McNamara favored advanced and detailed reviews of problems prior to beginning a crash program. The new government of Lyndon Johnson eventually adopted McNamara's approach.

One of the most serious problems facing SST development was the issue of “sonic booms.” Sonic booms happen when an aircraft's shockwave, which spreads behind an aircraft like the bow wave of a ship, produces a moving wall of compressed air that trails along the ground, often in a swath 50 miles (80 kilometers) wide. All those within this swath hear a boom when the shock passes. During experimental flights to verify the frequency of sonic booms, thousands of people in and around Oklahoma City, where the test flights were being conducted, had complained of the loud booms. Eventually, a very vocal environmental movement began to oppose development of the SST on the basis of noise pollution. There were other problems too: the prime contractor for the SST, Boeing, was mired in repeated design changes for the aircraft. Many who had supported the development of the SST, including key economists, began to believe that it would not be able to operate profitably. Finally, many disagreed on the proper role of government in the project. In 1971, Congress finally killed the project in the face of overwhelming public opposition.

In some sense, the demise of the American SST seemed to show that the future of commercial aviation lay not in planes that could fly faster and higher but in technologies that would be less apparent to passengers. Consequently, most of the technological advances in recent years have focused on areas such as ground-based traffic control and making planes less dependent on ground-based controllers. The FAA has already decided to use Global Positioning System (GPS) satellites to help accurately determine the location of aircraft in the air. The Air Force originally developed the GPS for military operations but its use in civilian passenger transport could revolutionize commercial aviation. GPS gives exact locations and also helps determine precise navigation paths, makes low-visibility landings easier, allows accurate navigation over the sea, and permits planes to maintain safe separation along particular routes. Continental Airlines was the first airline to experiment actively with GPS systems. Other advanced navigation systems include the Traffic and Collision Avoidance System (TCAS), which uses onboard radar to alert airplanes of nearby traffic. Further advances in commercial aircraft would include the development of more advanced turbofan engines that have very high thrusts and excellent performance characteristics. Such engines have already been used on the Boeing 777.

Of all the possible advances in commercial aviation, the two most talked about options remain the path of bigger and faster aircraft. In terms of big jets, there has been much talk of a passenger airplane, twice the size of the legendary Boeing 747, capable of carrying as many as 800 passengers. Airlines would benefit from such huge jets since they would have to buy and maintain fewer aircraft. Airports in turn would also have to accommodate fewer aircraft, but to accommodate these behemoths, airports would have to extend runways, strengthen aprons, and build new on-loading and off-loading systems.

Equally challenging for airports, Europe's Airbus consortium has plans for a giant passenger aircraft, the A380, capable of seating more than 550 passengers, which is scheduled to go into service in the year 2006. Although it was originally a joint project with Boeing, the American manufacturer dropped out early on believing that there would no demand for such a huge passenger airliner. Already, however, such carriers as Qantas, Air France, Emirates, Singapore Airlines and the American aircraft leasing company International Lease Finance Corporation (ILFC), have put in orders for the A380.

In terms of faster jets, after the debacle of the American SST, most airlines may have cooled off on the idea of faster is better, but proponents of supersonic and hypersonic transport remain vocal. Such planes would be a great boon to people traveling over very long routes such as across the Pacific. Although there may be a need for SSTs in the future, such planes would have to be technically advanced to avoid environmental costs, both in terms of sound and also damage to the ozone layer from supersonic engine exhaust, especially since these factors contributed to the demise of the original U.S. SST. Of course, perhaps the most important issue for both very large jets and high-speed transport would be cost. Since the 1960s, airlines—partly due to the economic downturn of the 1970s—have not been risk-takers. They have usually favored incremental innovation and foregone big leaps in technology.

The experience with the Concorde has not proven to be much of an encouragement. After the oil crisis of the early 1970s, the Concorde's high fuel consumption and small fuel tanks limited its operations to relatively shorter routes instead of the prized trans-Pacific market. Airlines generally found subsonic jets with their lower operating costs, more numerous seats, and larger cargo bays, much more lucrative. Although Air France and British Airways continue to operate the Concorde, they do so without much profit. After a catastrophic crash of a Concorde near Paris, France, in July 2000, the aircraft finally resumed operations in November 2001. Environmental complaints, however, continue to dog the program.

In the United States, since 1990, the National Aeronautics and Space Administration (NASA) has conducted its High Speed Research program focused on the development of a second generation SST known as the High Speed Commercial Transport (HSCT). During Phase 2 of the program, NASA even used the Russian Tupolev Tu-144LL supersonic passenger airliner as a testbed for various future environmentally friendly technologies. Boeing was one of the key participants in this program, but more recently has redirected its efforts to the development of the Sonic Cruiser, a passenger airliner (100 to 300 seats depending on the model) capable of Mach 0.95 and very-long ranges. Despite the interest in the HSCT and the Sonic Cruiser, and the expectation that global passenger travel will grow by 5 percent every year until 2015, there seems little likelihood that any high-speed passenger aircraft will fly the skies in the next decade. The economics and the environment remain against them.

Note: This article was commissioned by and first appeared on NASA's U.S. Centennial of Flight web site. It appears here with permission. We gratefully acknowledge both the author and NASA.