Boeing Co's long-delayed and hotly anticipated 787 Dreamliner is a case study in the growing pains that can accompany engineering innovation.

The revolutionary carbon-composite airplane is now two years overdue for its first test flight, which is set for the fourth quarter of 2009.

Meanwhile, Boeing and its customers are eager to see if the Dreamliner lives up to its promises of greater fuel efficiency, better environmental performance and increased comfort for passengers.

This airplane is a revolution, said Dennis O'Donoghue, vice president of Boeing Test & Evaluation. Composites offer a tremendous amount of advantages.

Boeing dubbed its new plane the Dreamliner in 2003 after dropping its concept for the Sonic Cruiser in response to airline demands for greater fuel efficiency rather than greater speed. The 787 development team includes aerospace companies from around the world.

At the heart of the Dreamliner concept is composite materials, which make up 50 percent of the primary structure and are much lighter than aluminum, which makes the skin of traditional commercial airplanes.

The lighter structure allows the 787 to consume 20 percent less fuel than comparable aircraft and also run quieter. At a time when airlines are battered severely by volatile fuel costs, this is a huge selling point for the Dreamliner.

The composite materials do not fatigue and therefore require fewer maintenance checks. Boeing says the 787 costs 30 percent less to maintain than competing aircraft. The plane also has improved aerodynamics, which increases efficiency 7 percent, Boeing says.

Additionally, the 787 features what Boeing calls open architecture, allowing for easier upgrades.

The 787 family will feature three models: the 787-8, which can carry up to 250 passengers; the 787-9, which will carry up to 290 passengers; and the shorter-range 787-3, which will carry up to 330 passengers.

The 787-8 is set for first delivery in 2010. The 787-9 is expected to be delivered in 2013. No date has been set for delivery of the 787-3.

(Reporting by Kyle Peterson, editing by Matthew Lewis)