Bulgaria's defence ministry said on Tuesday that it has invited Russia's United Aircraft Corporation (UAC) and Belarus' 558 Aircraft Repair Plant (ARP) to submit offers for a contract for ensuring the airworthiness of the country's Su-25 fighter-bombers. The estimated value of the contract is 41 million levs ($24.2 million/21 million euro), the defence ministry said in a procurement notice. The overhaul of the Su-25 ground attack aircraft is already 10 years overdue, the ministry noted. The ministry's decision can be appealed before the Commission for Protection of Competition within 10 days since its publication.