Further stress testing of the Irkut MC-21 wing box has indicted that the structure will be able to withstand maximum flight loads.
Irkut had stated earlier this year that it would need to reinforce the MC-21's wing box because, despite coming close to passing a destructive test, it had not achieved the strength threshold required.
The airframer proceeded to commence flight testing of the initial aircraft in May.
But the composite wing has undergone additional stress testing at the Moscow-based Central Aerohydrodynamic Institute.
The institute says it has completed the latest phase of tests on the wing box in mid-November, in order to ensure the safety of the MC-21 flight-test fleet.
It states that the wing box "withstood a load exceeding that specified by the test programme, without damage".
Although it has not disclosed further details the institute says this has "confirmed" that the wing box has "sufficient strength" at maximum flight loads.
Irkut has been preparing a second flight-test MC-21 to join the campaign with further test aircraft at various stages of construction.