According to Russian "Kommersant" newspaper the official representative of TH&C holding- the parent company of the perished charter plane said that the plane underwent a D-Check procedure last year (according to the rep D-check takes place every 12 years of service and takes 30-40 days in a special tech facility with all the major components and systems tested and replaced if needed). In addition the certificate (of airworthiness?) has been confirmed this year...