Russian airframer Irkut confirms it will need to strengthen the wing of the MC-21-300 twinjet after it failed a destructive test before reaching ultimate load.
Irkut tells FlightGlobal that the wing box has been stressed to destruction in line with the test programme.
During ultimate-load testing the wing is required to withstand stress forces 50% greater than the limit load – the maximum it could expect to encounter in operational service.
But Irkut admits that destruction of the wing occurred under a load "a very few percent" below the threshold required.
It says the MC-21's wing is the Russian aerospace industry's first experience in creating a high-load composite structure.
"The decision has been made to implement strengthening of the wing structure in parallel with pre-flight testing of MC-21-300 aircraft systems," the airframer adds.
Irkut points out that this will mean modifying the wing without de-mating it from the fuselage.
"This approach will enable non-interruption of flight tests," it states.
Reinforcement of the wing box will add around 25kg to the weight, confirms Irkut.
Testing of the "maximally lightweight" wing had been undertaken at the Moscow-based Central Aerohydrodynamic Institute, which declined to provide further details to FlightGlobal.
Irkut says the wing has "reserves" of strength, proven during the testing, which validate the design and provide sufficient margin to commence flight tests.
The wing structure for the MC-21 is manufactured by AeroKompozit in Ulyanovsk, which has not commented on the test results.
While the wing's failure to reach ultimate load is a setback, a similar situation emerged during development of the Airbus A380. The double-deck aircraft's wing fractured before reaching ultimate load in February 2006.
Irkut rolled out the Pratt & Whitney PW1400G-powered MC-21 at a ceremony in June last year. No date has yet been fixed for its maiden flight.
It is designed to replace older types such as the Tupolev Tu-154 and Tu-204, and be capable of transporting 163-211 passengers over a range of up to 6,000km.