Basler Aviation AG -Belair- was founded by Balz Zimmermann in 1925 in Basel. The name Blair is a reference to the French name of the Basel. The first route was from Basel to Freiburg and Mannheim. Bel Air grew rapidly. In 1929 Basel Airport was the largest airport in Switzerland, with direct flights to Zurich, Geneva, Lyon, Karlsruhe and Frankfurt. In response to the Great Depression, Bel Air (based in Basel) and Ad Astra Aero (based in Zurich) merged on 1 January 1931 to form Swissair, headquartered in Zurich. Up to that point, Blair had carried over 18,000 passengers, 320 tons of cargo and 143 tons of mail. The company only flew in the summer and was mainly financed by federal subsidies and transportation of mail for the Swiss post office.