Air Baltic Corp., Latvia’s flag carrier, agreed to turn seven options for Bombardier Inc.’s CS300 jetliner into a firm order, bolstering the planemaker’s beleaguered C Series program. The seven aircraft are valued at about $506 million based on list prices, Montreal-based Bombardier said Tuesday in a statement. AirBaltic will become the first operator of the CS300, which can seat as many as 160 passengers, when deliveries begin in the second half of the year. The airline now has 20 C Series aircraft on order. Bombardier is working to line up blue-chip customers for its flagship jet amid stiff competition from Boeing Co. and Airbus Group SE, the world’s biggest planemakers. The state-of-the-art C Series, with composite parts and efficient fuel consumption, is more than two years late and more than $2 billion over budget as it nears its commercial debut when Deutsche Lufthansa AG’s Swiss International arm flies the CS100 in the third quarter. Class B shares of the Canadian planemaker climbed 4.7 percent to C$1.34 at 10:16 a.m. in Toronto. While AirBaltic’s order boosts the C Series’ firm-order backlog to 250, Bombardier so far is 50 aircraft short of its target of 300 by the time the jet enters service. Air Canada, which signed a letter of intent for at least 45 CS300s in February, has yet to turn that commitment into a firm order. Including firm orders, conditional sales and options, Bombardier now has commitments for 678 C Series aircraft.