* Carbon-fibre jet "behaving well," chief pilot says
* Joins Boeing 787 in new generation of lightweight jets
* Competition expected to dominate Paris Airshow
By Tim Hepher and Jean Décotte
TOULOUSE, France, June 14 (Reuters) - Europe's newest jetliner, the Airbus A350, successfully completed its maiden flight on Friday, stepping up the battle with arch-rival Boeing for sales of a new generation of sleek, lightweight passenger aircraft.
Watched by more than 10,000 staff and spectators, the aircraft's curled wingtips sliced into clouds above the Airbus factory in southwestern France and flew over the Pyrenees mountains, with a crew of six wearing orange jumpsuits and parachutes.
The flight, with two former fighter pilots at the controls, lasted about four hours and capped eight years of development estimated to have cost $15 billion.
"The airplane is behaving extremely well," said British chief test pilot Peter Chandler, speaking by radio link from an altitude of 13,000 feet.
French co-pilot Guy Magrin took the controls for the take-off at 10:01 local time (0801 GMT), giving the plane air under its wings for the first time in front of a podium of airline chiefs who have ordered 613 aircraft.
It touched down at 14:05 local time, after flying past the Toulouse production site.
"It is a great day for Airbus. A maiden flight doesn't happen that often. It is not like the auto industry, where you launch a new model every two years or even less," said Tom Enders, the head of Airbus parent EADS.
The long-awaited sortie is a milestone for Airbus as it battles against Boeing's 787 Dreamliner for sales of a new generation of lightweight jets made from carbon-plastic material designed to save fuel and open up new long-distance routes.
Boeing was quickest off the mark with the revolutionary carbon-composite technology and its Dreamliner has outsold the A350 with sales standing at 833 aircraft for 57 customers.
Airbus hopes to catch up and also mount a challenge to the U.S. manufacturer's larger, metallic 777 using a later version of the A350.
Airbus's ebullient New York-born sales chief, John Leahy, lost no time in talking up the plane's benefits moments after its Rolls-Royce engines opened up to full power.
"Did you hear how quiet it was? We are going to set new standards ... People round airports won't even know we are taking off," Leahy said.
Didier Evrard, a top European missile developer who was selected to run the A350 programme because of its complexity, smiled broadly but refused to relax.
"I will still be nervous until it comes back. I'm an engineer so I have to be connected to the ground and make sure everything is fine," he said during the flight.
Competition for wide-bodied jets is expected to dominate next week's Paris Airshow, where the A350 could steal attention with a brief roar over the aviation industry's largest showcase.
Airbus is finalising orders from Singapore Airlines , Kuwait Airways and Air France and may add a new customer at the June 17-23 show, analysts say.
Evrard said that Airbus would soon add a customer in the United States, where industry sources say that United Airlines is negotiating to upgrade and expand an existing order to 35 jets.
Airbus initially dismissed the threat posed by the new generation of mid-sized aircraft as it focused on building the world's largest airliner, the A380 superjumbo.
But faced with burgeoning Dreamliner sales, it changed tack and overhauled the design of the A350 by adopting similar composites technology in 2006.
To boost sales, Boeing is expected to confirm plans to build a larger version of its Dreamliner. It is also overhauling its 777 with new engines and wings.