There's one major obstacle in the supersonic business jet flight plan: FAR 91.187.

It is the rule that prohibits any flight of a civil aircraft from reaching or exceeding Mach 1 to or from an airport in the U.S., unless it will "not cause a sonic boom to reach the surface within the U.S." And it will have to be amended come the time supersonic bizjets become a booming business.

To that end, the FAA is working with the Partnership for AiR Transportation Noise and Emission Reduction (Partner) Center of Excellence--a group of nine universities headed by the Massachusetts Institute of Technology--to examine the feasibility of overland supersonic flight.

The U.S. government last looked at supersonic flight in the early 1990s, when NASA conducted some work on it, says Carl Burleson, FAA director of the office of environment and energy. In 2003, the Defense Advanced Research Projects Agency (Darpa), in conjunction with NASA and Northrop Grumman, ran tests on a quiet supersonic platform with a modified F-5 to determine if they could shape the N-wave that is characteristic of a sonic boom (see p. 68). The researchers had some success, and demonstrated the accuracy of their computer programs' predictions, he added.

Advances in materials, computer models and computational fluid dynamics spurred further action.

As traditional metrics used for aircraft noise aren't applicable to business jets, the FAA approached the research community "to come up with an acceptability metric," says Burleson. In September 2003, the Partner Center of Excellence was formed. Two months later, the agency held a public meeting, the Supersonic Workshop, to solicit technical information from agencies, industries and universities about the mitigation of the sonic boom.

In addition, the FAA started a process within the International Civil Aviation Organization to seek international opinion on modifying the supersonic standard, or developing one for supersonic overland flight, says Burleson.

The Partner Center is also working to develop simulators reflective of actual sonic booms. Burleson says the FAA is hopeful Partner will have "at least an interim metric sometime next year."

Decisions about building a demonstrator aircraft based on that set of metrics would follow. While NASA had expressed some interest, it has not yet been determined who will finance or build it, says Burleson.

He noted that data from Concorde operations are not applicable to business jets. "The Concorde is '60s technology," says Burleson. "The supersonic business jet's sonic boom is very different from that of the Concorde. It's less intense."

Burleson also notes that supersonic overland flight may require a change in U.S. law, as the original ban on such flight was an act of Congress.

All in all, it's going to be "quite a challenge," said Burleson. "It's one thing to develop a scientific metric. It's another to develop a public consensus."