Manchester Airports Group (MAG) said on Wednesday that it is partnering with Chinese state-owned Beijing Construction Engineering Group (BCEG) in a bid for a 35-year concession contract for the operation of Sofia International Airport. MAG's strategy focuses on introduction of more routes from Sofia to Belgrade, Zagreb, Sarajevo and Tirana, as well as all other European capitals, the UK airport operator said in a statement.MAG also operates two of the most important cargo airports in the UK and understands the importance of cargo routes, the company noted. The airport operator has been studying the potential of Sofia Airport for over two years and the airport might become its largest investment outside the UK, it also said. Manchester Airports Group operates three airports in ritain - Manchester, London Stansted and East Midlands. The combined annual passenger traffic of the three airports totals nearly 60 million. The estimated value of the concession contract is 3.9 billion euro ($4.5 billion), Bulgaria's transport ministry said in August, when the tender was launched. The deadline for submitting offers in the tender is October 12.($ = 0.8623 euro)