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(Reuters) - The final countdown is under way to the maiden flight of the Airbus EAD.PA A350, Europe's answer to the Boeing (BA.N) 787 Dreamliner.
Once test crews accept the first A350 from developers, these are key steps to the first flight, based on previous programs.
* First, engineers at Airbus headquarters near Toulouse in southern France will turn on the Auxiliary Power Unit, a small turbine engine under the tail, used for power on the ground. The test will last just 1 minute to see if it leaks of oil or fuel.
* Crews check circuits and aircraft systems, one by one, and run the air-conditioning under APU power.
* Two Rolls-Royce (RR.L) engines are started one after the other, again briefly at first, to detect any oil or fuel leaks.
* Hydraulics and other systems run with the engines on.
* Engineers test "bleed air," a traditional conduit of air from the engines used for cabin pressurization and de-icing. This is a crucial design difference with Boeing's rival 787 Dreamliner, which relies more on electrical system.
* Engineers progressively squeeze power out of the engines in a "run-up" area, like a concrete paddock, with brakes on.
* In parallel, the aircraft will start to move under its own power, slowly at first, and then up to 60 knots (111 km/h).
* The plane's pre-flight workout end when the six pilots and flight engineers don orange jumpsuits, parachutes and life-vests for a rehearsal, pushing the plane close to its take-off speed.
* Ground mechanics carry out a thorough two-day inspection.
Six crew with parachutes take part, three in the cockpit and three at consoles in the passenger cabin. Instead of seats, the cabin contains water vats to simulate the weight of 300 passengers. A maiden flight usually lasts 4 to 5 hours.
Pilots need a day when wind is blowing from the west so as to use a northwesterly runway, avoiding flying over Toulouse.
To maintain maximum control of events, test pilots take off in a fully manual "direct" mode without computer protection.
The next critical milestone is when flight test crew retract the landing gear, once a safe altitude is reached. (On the A380 maiden flight in 2005, the gear failed to retract properly).
This will determine whether they can go higher and faster to get their first feel of the aircraft in cruise conditions.
The flight will also be the first chance to study behavior that no simulator or wind tunnel has so far been able to predict, such as the airflow at slow speeds near the ground.
A dozen flights should be enough to give a verdict on basic performance, but at least 2,000 hours of development and safety certification tests lie ahead before the A350 can enter service.
MEDIA - The event will be televised and is certain to be beamed back to the Paris air show if the A350 flight happens during the June 17-23 event. Headlines will focus on the take-off but for test pilots this is surprisingly routine. Their real challenge starts later in the flight and in subsequent testing.
INVESTORS - Analysts say investors in Airbus parent EADS EAD.PA are hungry for minute details on the tests. A first flight usually supports shares, but this is not always the case.
In the month after the first outing of the 787 in December 2009, Boeing shares rose 9 percent, Thomson Reuters data shows.
The almost simultaneous debut of the Airbus A400M military plane kicked off a 17-percent one-month rally in EADS shares.
But the A380 first flight in April 2005 failed to prevent a 10-percent decline over the following month as the program was delayed six months and EADS failed to quell management tensions.
BOEING - Few will be watching Airbus with greater interest than its U.S. rival 5,000 miles away in Seattle. It is anxious to preserve a sales edge for the 787 after a three-month grounding caused by problems with fires in batteries.
It hopes to make a mark at the Paris air show with plans for a revamped 777 and may launch a stretched version of its 787.
AIRLINES - As technology advances, new plane launches are increasingly late and some buyers are taking little on trust.
After delays, one of those demanding hard evidence from the early testing is the head of Dubai's Emirates, Tim Clark.
At stake are dozens of potential orders for a revamped Boeing 777, or an upcoming larger version of the A350, or both.
"As Airbus knows, I want to see it on its wheels with its engines running and preferably in the air," Clark said in an interview at a recent trade show. "I am afraid I am not prepared to accept anything until I see telemetry giving performances of the engines and the fuel. The A350-1000 is definitely one that we would be looking at. But first of all - show me."
Sources: "The A380 flight trials," by ex-Airbus flight test chief Claude Lelaie; Reuters interviews; Thomson Reuters data.
Reporting by Tim Hepher; Editing by Alastair Macdonald