Qantas' first Dreamliner has taken to the skies above Seattle as the airline prepares to launch its Perth-to-London services.

The 787-9 is due to join the airline around the middle of this month after completing a test programme in the United States.

The aircraft is the first of its eight Dreamliners that will join the Australian airline's fleet.

Qantas 787-9s will feature a premium-heavy 236-seat interior with 42 seats in business class, 28 in premium economy and 166 in economy.

Advertisement

Qantas' Perth-London service will operate through Qantas' existing Perth domestic terminals (T3/4), which are being upgraded with new facilities and lounges to accommodate international flights.

The 14,498km flight will take about 17 hours and, when it launches next March, is expected to be the third-longest passenger flight in the world.

It will also be the longest Boeing Dreamliner flight in the world.

Qantas chief executive Alan Joyce has said the airline was conscious it was a long flight, but not much longer than the airline's Sydney to Dallas service.

"It's the kind of route that the Dreamliner was created for, because of its built-in features to reduce jet lag and improve the overall travel experience." he said.

Direct routes tended to stimulate new travel demand by making it easier to get to a destination, said Joyce.

The aircraft, largely made of carbon fibre, entered airline service with Japan's ANA in 2011 after development and manufacturing delays but has been a success for airlines.

It is typically more than 20 per cent more fuel efficient than aircraft it replaces and so far close to 200 million people around the world have already flown on 787 Dreamliners.