The design of the center wing box of the Comac C919 narrowbody aircraft has passed its critical design review, and managers of the Chinese program have authorized the next stage in the composite structural design.

Comac’s announcement on the critical design review did not mention the material that will be used for the center wing box.

It has been designed as a composite structure mated to aluminum outer wings, program officials have said. But the company also has prepared an alternative plan for an aluminum center box.

In general, the aircraft’s preferred structural system has used a mix of composite and metal parts similar to that of the Airbus A380.

A committee reviewed reports on the composite structural design this month, Comac says. The group also looked at progress in making that structure and approved further work.

The manufacturing program for the center wing box also was assessed.

The C919 is due to make its first flight next year, although program officials last year said this would be achieved only if there were no delays.

Entry into service is scheduled for 2016.

Wu Guanghui, Comac deputy general manager and C919 chief designer, told the design review meeting that while the latest progress indicated a certain degree of success for the program, challenges remain.