No city-county agreement may matter more to the Wichita economy than the one keeping low-fare AirTran Airways serving Wichita Mid-Continent Airport. To its credit, the Wichita City Council unanimously voted Tuesday to approve another year of the agreement, under which the city and county each will contribute up to $875,000 while the state contributes $4.75 million. Sedgwick County commissioners are unlikely to present a similarly united front when they take up the agreement today. But especially with AirTran now owned by low-fare king Southwest Airlines, what matters is that the county and city remain committed to keeping Wichita air service as affordable and strong as possible. If not, Wichita could relive 1997, when Vanguard Airlines exited town and local fares shot up as much as 223 percent.