The Bulgarian Ministry of Defence (MoD) on 21 August published a tender inviting Russian and Belarusian state-owned companies to negotiate a framework agreement valid for 48 months to overhaul the Bulgarian Air Force's (BuAF's) Su-25 close air support aircraft in 2019-22.
The invitations were sent to Russia's United Aircraft Corporation and to Belarus's 558 Aircraft Repair Plant. These state-controlled entities were identified by the MoD as capable of providing maintenance and lifecycle extension services for the BuAF's fleet of 10 single-seat Su-25Ks, four twin-seat Su-25UBKs, and their 28 R-95Sh turbofan engines.
The two companies were invited to provide their initial bids by 10 September, with negotiations scheduled to take place in Sofia two days later.
Read more here