Boeing plans to complete a fourth and final round of Sonic Cruiser meetings with airlines around September before seeking authority from the Boeing board to offer the high-speed airliner as early as October.

Sonic Cruiser vice-president Walt Gillette says failure to secure board approval by year-end would not be "a show stopper". But he adds: "The sooner we can make it, the quicker we can focus on one area, such as size or range." However, to stay within reach of a 2008 entry-into-service target date, the programme does not officially need to be launched until 2004, he says.

Technology features for the design are due to be downselected next year, while firm configuration is expected to be frozen in late 2004 or early 2005. The company is midway through a third round of airline presentations, which it expects to complete by the middle of this month. The fourth and final round, Boeing hopes, is set to take place in "late summer or early fall", says Gillette.

Boeing says airlines are being shown the baseline, aft-wing Sonic Cruiser design as well as a mid-wing concept and the "reference" aircraft, a 250-seat advanced technology conventional design dubbed "Yellowstone" (Flight International, 2-8 July).

The mid-wing concept eliminates the forward canard which, although essential to the stability of the low-drag configuration of the aft-wing concept, poses issues for jetway compatibility.

"One of the trades we are running is taking the canard off, and taking that aft wing and moving it forward," says Gillette. The longer design requires horizontal tail and fuselage contouring to achieve transonic cruise. This would pose manufacturing issues and add to the complexity of stretching the aircraft's design.

"It is a highly evolved trade study, and we'll keep going until we have a clear winner or we validate that the aft-wing design is clearly the best," he adds.

Continued interest is also being shown in the conventional design, which Gillette insists is still strictly a reference. "We are still applying technology against a conventional airframe because we have to know the benefits." If sufficient market interest continues in the reference design, Gillette does not rule out the possibility of Boeing launching the conventional model as a hi-tech running mate to the Sonic Cruiser.

The aircraft could be the basis for a 757/767 replacement, but is not the focus for the current product development effort. However, co-development is "possible" says Gillette, adding: "We will build the aircraft the market wants."

Boeing is also tackling the question of whether to launch two Sonic Cruiser family members at once or separate their introduction by six months.

Two initial family members are being considered - a lower empty-weight model with a 12,200km (6,600nm) range and a heavier variant with the ability to fly a longer transpacific range of up to 15,500km.

Source: Flight International