Those boarding bridges that connect aircraft to the concourses at Des Moines International Airport are starting to show signs of their age, so the airport board has plans to replace them. Most of the 12 passenger boarding bridges at DSM International’s gates are 33 to 35 years old — enough to concern airport officials about potentially disruptive breakdowns. At its monthly meeting last week, the board approved a contract to replace four of the bridges this year, with plans for seven more to be replaced over the next two years. One of the newest bridges, at Gate A5, won’t be replaced. The cost for the first three bridge replacements totals $168,500, a figure that was included in the airport’s fiscal 2020 budget. Bryan Belt, the airport’s director of engineering and planning, informed the board that the bridges are being designed so they can eventually be used at the planned new airport terminal as well.