On July 5, 2011, the U.S. District Court for the District of Columbia issued an order concluding that the U.S. Environmental Protection Agency (U.S. EPA) has a mandatory obligation under the Clean Air Act to consider whether the greenhouse gas and black carbon emissions of aircraft engines endanger public health and welfare.  This issue is critical because the Clean Air Act explicitly requires U.S. EPA to regulate emissions that it determines as endangering public health and welfare.  Based on its conclusion, the court refused to dismiss a complaint filed by environmental interest groups seeking to compel U.S. EPA to proceed with the regulation of non-road vehicles and aircraft.