Airbus has started final assembly of the final airframe in the A350 test fleet, MSN5, following delivery of the three fuselage sections to Toulouse.
MSN5 will be the second aircraft to be fitted with a passenger cabin for testing, after MSN2.
It will be used to conduct early long flight trials, to simulate in-service operations, as well as route-proving flights.
Airbus says MSN5 is scheduled to perform its first flight in spring 2014.
Its first two flight-test aircraft, MSN1 and MSN3, have performed more than 100 sorties and logged over 500h.