All four unsuccesful bidders in the tender for a 35-year concession contract to run Sofia Airport have filed complaints against the Bulgarian transport ministry's ranking of the offers, data by the country's competition authority shows. UK's MAG Overseas Investment and Aeroports de Paris (ADP) filed complaints on Friday, while Fraport Bulgaria and Swiss-based SSB Sauerwein & Schaefer Bau challenged the ranking on Monday, according to data published on the website of the Commission for Protection of Competition.Earlier this month, Bulgaria's transport ministry ranked as the best offer the bid submitted by the Sof Connect consortium led by French investment firm Meridiam Eastern Europe Investments, with Flughafen Munchen named as airport operator. The consortium's offer was awarded 86.12 points out of a maximum score of 100 points. The winning consortium offered to pay a concession fee of 24.5 million euro ($27.5 million) per year for the duration of the contract and pledged to make investments of 608 million euro in Sofia Airport.The ADP-led consortium, which also includes the company's Turkey-headquartered unit TAV Havalimanlari Holding, was ranked second with 80.31 points. Fraport Bulgaria, the local unit of Fraport AG Frankfurt Airport Services Worldwide, came in close third with 80.19 points.The MAG-led consortium was ranked fourth with a score of 78.42 points, followed by SSB Sauerwein & Schaefer Bau with 66.15 points.