US regional carrier Mesaba Airlines says it is to buy Billings, Montana-based Big Sky Transportation for around USD$3.5 million. Big Sky flies to 20 cities in five states with a fleet of small turbo-prop planes. It started operations in 1978 and four years ago took over services flown by bankrupt Aspen Mountain Air. Mesaba, a much larger carrier which operates feeder services on behalf of Northwest Airlines, plans to make its new acquisition a wholly-owned subsidiary. "Big Sky is a good example of the type of opportunity we are seeking," said Paul Foley, Mesaba's president and chief executive. "It is an efficiently run company with an excellent safety record and a cost structure that positions it well in the highly competitive regional airline marketplace." Last month, Minneapolis-based Mesaba announced it was furloughing 50 pilots and closing bases as part of cost-cutting measures.