Airbus's roll-out and first flight of the A350-900 prototype will not ease the pressure on the airframer's flagship twinjet programme, but simply give it a different nature.
The first aircraft's entry into the flight-test phase marks only the beginning of a phased certification effort which will require completion of another four A350s.
Airbus's attention is turning increasingly towards the production ramp-up as well as the development of the A350-1000, after a year in which the largest member of the family has attracted orders from several high-profile customers.
But progress on the -900 will not advance the schedule of the -1000, insists A350 programme manager Didier Evrard.
"There is no change here," he says. "We are going step by step. The ramp-up of resources will be very high this year."
Design and technology insertion for the -1000 has been frozen, he says, and specific design work is in progress. The -1000 is due to enter final assembly in the second half of 2015, with the aircraft's first flight set to take place a year later, before entry into service in 2017.
"What was really interesting in the last few months was to see the -1000 orders growing," says Evrard. "The -1000's endorsement is confirmed."
British Airways' decision to select the type as a Boeing 747-400 replacement follows conversions and orders from Cathay Pacific, Qatar Airways and Air Lease, secured after the variant's redesign in 2011.
Evrard says the -1000's development will benefit from the re-use of several major components built for the -900, including the hydraulics, air generation system, wing fuel pumps, integrated avionics, electrics and flight-control equipment.
Airbus parent EADS suggested in May that the -1000 could require the airframer to seek extra assembly capacity, although it has not indicated whether this might best be achieved by efficiency measures at its Toulouse plant or through extending its facilities.
However, the airframer's priority is the production of the A350-900 flight-test fleet. Prototype MSN1, which was rolled out on 13 May, and MSN3 - the second to enter final assembly - will be the primary airframes for flight-control testing, both heavily instrumented for the purpose.
MSN1 carries a flight engineer test station, 8.4t of acquisition racks and some 338km of harnesses, as well as water ballast tanks to adjust the centre of gravity.
"It's quite an exercise to install all this on top of what's already in the aircraft," says A350 chief engineer Gordon McConnell. But he adds that the tanks enable water transfer in flight, saving the need to land to alter the aircraft's balance.
MSN1's tasks will include natural icing tests, while MSN3 - due to fly in late September or early October - will undertake the high-altitude campaign, as well as hot and cold performance testing.
The other three prototypes will be introduced to the certification programme over the first four months of 2014. MSN2, flying in January, will be the first fitted with an interior cabin, and will be used for early long flight and initial evacuation assessment.
MSN4 and MSN5, active from February and April next year respectively, will each be lightly equipped with instrumentation. MSN4 will be used for external noise analysis but MSN5 - which, like MSN2, will be cabin-equipped - will conduct the route-proving and extended twin-engined operations (ETOPS) tests.
Airbus has taken advantage of the certification work on the Rolls-Royce Trent XWB powerplant to advance other work on A350 systems.
It has used the engine in conjunction with hydraulic pumps to supply the green hydraulic circuit on A380 MSN1 - the aircraft serving as an airborne testbed for the Trent XWB. Like the A380, the A350 will have a dual-circuit hydraulic system operating at 5,000psi.
Airbus has also flown some of the aircraft's avionics and the radio-altimeter. "It saves us a bit of time on the A350 test campaign," says McConnell. "We're looking at the maturity of the systems and trying to improve that maturity. It's been well worth it to do these [early tests]."
Airbus has just completed natural icing and drainage tests as part of a third phase of flight testing on the A380 - the objectives for which also include assessment of air inlet distortion.
The first Trent XWB, for the A350-900 and smaller -800, achieved certification in February. Twelve engines in the test campaign have accumulated around 4,000h and have carried out 6,850 cycles, with 69 flights on the A380 - covering 237h - logged by mid-May.
"That's much more than we've done with any past programme," says McConnell.
Higher thrust requirements for the A350-1000 will demand an enhanced version of the powerplant, the XWB97, and a prototype demonstration is set for 2013, with the first engine run taking place a year later.
Airbus started flying the A350 at the end of January - at least in a virtual sense - through its integrated Aircraft Zero rig, which connects a cockpit simulator to the "iron bird", which represents the hydraulic and electrical systems on the aircraft.
Twenty flight crew have regularly participated in the tests, and some 700 virtual flight sessions have been used to verify system functions, including potential degradation and failure scenarios, to ensure maturity before first flight.
"We were running complete flight sequences on this rig," says McConnell, adding that Aircraft Zero uses 1,500 different pieces of software. "It's about as close to the aircraft as it can be without having the aircraft itself."
These virtual test runs have gradually converged with the development of MSN1, which underwent fuselage assembly - the Station 50 point on the Toulouse line - in the third quarter of last year, before moving to Station 40 for wing join and full power-on electrical testing, and initially emerging towards the end of the year as it transferred to Station 30 for system tests.
Once the aircraft's wings had been fully equipped with its high-lift control surfaces and winglets, MSN1 underwent Station 18 testing outside in late February.
"There were high winds," recalls McConnell. "We were wondering which piece of ground equipment was going to blow into the aircraft."
Tests were performed on MSN1's fuel system as well as radio communications, cabin pressure and ram-air turbine deployment. McConnell says: "The aircraft survived, it got past the tests and we took it inside again quickly."
MSN1's engines and auxiliary power unit were fitted in March and the aircraft entered the final stretch of ground testing to prepare the twinjet for its maiden flight.
As part of this final stage the aircraft was subjected to a nine-day ground vibration test, with 500 accelerometers mounted at various points to identify vibration modes, to "secure flight envelope opening", says McConnell.
MSN1 also underwent a calibration test to validate some 200 strain gauges for flight-test load monitoring. "It's probably the most risky thing we did," says McConnell, referring to the heavy mechanical booms which had to be placed in close proximity to critical sections such as the fin. "We were a bit nervous with that thing swinging around up there," he says.
Lightning-strike testing was conducted on MSN3 to demonstrate the effectiveness of the copper foil mesh bonded to the carbonfibre fuselage. The test current was about 1-2A but "very high voltage", says McConnell, and the results were extrapolated upwards.
But a third A350 has been crucial to MSN1's first flight preparations. MSN5000 - also known as Essai Statique - is the static airframe located in Airbus Toulouse's building L34, in a 2,500t rig originally used for the A380 and adapted. As well as structural modifications the enhancements include 12,000 sensors, compared with 10,000 used for the A380, to compare recorded data against increasingly detailed finite-element modelling.
MSN5000 comprises a full fuselage and wing boxes, with dummy components to represent loads from the undercarriage, horizontal stabiliser, upper vertical fin, tail cone, wing tips and pylons.
Static testing commenced at the end of March. The airframe will be used to assess a range of load cases involving fuselage and tank pressurisation - up to 1,327mb - as well as structural bending, to ensure there is no permanent deformation of the composites.
By mid-May it had already been used to analyse all cases at 80% of limit load and most at 100%, says A350 static major test manager Emmanuel Bodin.
But the airframer also prioritised testing at 125% of limit load - at least for selected cases - ahead of the first flight, with the remainder to be performed afterwards.
"It's a choice we've made to do [this testing]," says McConnell. "It's not a load you see every day."
He says the airframer wanted to "have more margins" for the flight-test programme. "Occasionally when you go to the [normal] limit on the flight-test programme you have to have an inspection if you've exceeded the load," he says.
This involves grounding the aircraft for examination, he says: "To avoid any stoppage like that we wanted to go to [125% of limit load], and we think that was a good decision."
Airbus's first-flight clearance tests have included a dedicated full-scale analysis of the root attachment for the A350's vertical fin, completion of a high-lift device campaign using a rig in Bremen and final software tests on the landing gear system.
Separate loading tests, focused on the wing, have been carried out at Erding in Germany, using the EW rig which replicates the left-hand wing box, along with structures to represent the centre wing box, main landing-gear, engine pylon and control surfaces.
Airbus performed 1g wing-bending tests on the EW rig at the end of March. "This was mainly to look at system runs on the wing and make sure there were no potential clashes," says McConnell. "That was quite important to do."
As well as the 125% limit load testing, the airframe will be required to demonstrate resistance at ultimate loads of 150% as part of the certification programme.
"We'll eventually do damage tolerance testing on [the EW rig] for the carbonfibre," adds McConnell.
Fatigue tests for certification will begin this year, he says, with three separate rigs - designated EF1, EF2 and EF3 - being used respectively for work on the forward fuselage, the wing box and belly fairing and the tail cone.
While Airbus states that the A350-900 is a 315-seat aircraft, it revealed last year that the first cabin-equipped flight-test airframe, MSN2, would be fitted with a 252-seat configuration.
Tests on the interior will be performed on the Cabin Zero integration bench in Hamburg. "We'll be able to run all the cabin systems on here," says McConnell, adding that it is "on track" for virtual first flights.
Interior customisation for the A350 "developed strongly" last year, says Didier Evrard, with an initial supplier base for seats and in-flight entertainment expanding to cover more seat options, bars, floor-path markings and other equipment.
He says that Airbus has worked with more than 10 customers to define a set of interior configurations, and the airframer is finishing work on a full-scale mock-up in Toulouse and customer definition centre in Hamburg.
It is piloting a newly developed configuration tool with early customers with which "you can really build your layout," says Evrard. After selecting interior options from a catalogue, the customer is able to perform a visual walk-through of the cabin to see how it will appear. He adds: "It's a very impressive tool."
Towards the end of 2013 the airframer will start moving through the ramp-up gates for serial production, hiking the rate at the end of 2014 as the first aircraft are delivered.
Evrard says that while the emergence of MSN1 in its flight-test colour scheme was a notable step in the A350's development, Airbus has not designed the aircraft "just to roll it out of the paint shop".
Qatar Airways will be the first carrier to take delivery of the A350, and the Middle Eastern airline is assisting Airbus with entry into service preparation activities - covering such areas as training, technical data, maintenance and logistics.
Airbus is completely refurbishing its flight-line building to accommodate "airline-like" services, says Evrard, which will allow flight-test conditions to "mirror" carrier operations.
"We want to try to train ourselves in processes that we will then use, with our customers, to be very well-equipped and organised," he states.
Airbus remains supremely conscious of the pressures on the A350 programme, and the scrutiny it faces, particularly given that the timing of the crucial flight-test phase coincides with the glare of the 50th Paris air show.
Over the next 12 months the airframer will learn whether its maturity-above-all strategy has succeeded. Evrard is confident, but resorts again to the phrase which has become associated with the A350 as much as the maturity mantra - that the programme "remains challenging", adding: "It's not a given. It's not a given at all."