Ryanair Holdings Plc, Europe’s biggest discount carrier, plans to start operations from Sofia in October as it seeks to expand into smaller markets such as Bulgaria, Chief Commercial Officer David O’Brien said. Ryanair plans to invest $300 million to deploy three aircraft at the Sofia Airport and will operate 21 routes, O’Brien told reporters in the Bulgarian capital on Wednesday. Ryanair plans to carry 1.5 million passengers a year in 2017 from the Sofia and Plovdiv airports, up from estimated 700,000 people this year, he said. Destinations from Sofia will include Berlin, Barcelona, Valencia, Milan and Athens. “There’s the possibility to fly potentially from Sofia to 150 Ryanair routes out of Sofia,” O’Brien said. “That potential exists in the future. ” Ryanair will become the biggest foreign carrier at the Sofia Airport, which now has 52 international routes. The airline now operates flights to Standsted, London from Bulgaria’s second biggest airport in Plovdiv. The carrier has aircraft located in 82 bases in Europe with traffic estimated at 106 million passengers this year.