Boulder filed a federal lawsuit against the Federal Aviation Administration over issues surrounding the city’s plans to possibly close Boulder Municipal Airport. In a court filing Friday, attorneys for Boulder wrote that the city is considering redeveloping the airport amid a shortage of affordable housing and growing concerns around noise and environmental impacts from the airport. They noted that, while the city has previously accepted FAA grant funding for airport maintenance, each grant agreement Boulder accepts obligates the city to keep the airport open for a maximum of 20 more years.