The Air Force’s ordering a revised environmental impact statement will likely push final action to 2019. A National Guard proposal to expand airspace for fighter jet training low over the mountains of western Maine has dragged on for so long that many of the aircraft currently used for training could be retired by the time the plans are completed. Vermont-based F-16 fighters account for the bulk of the training flights and are due to be replaced by stealthy F-35 fighters that figure into the National Guard proposal to hold training exercises over a larger area. F-35 fighters aren’t allowed to fly low to the ground, and the guard says its plan would cut the number of low-flying jets by more than two-thirds each year and mean less noise from aircraft screeching overhead. “I can’t guarantee someone that they won’t hear an airplane, but I can guarantee that they won’t hear it consistently,” said Jamie Flanders, airspace manager. But a former fighter pilot instructor warned there are no guarantees on numbers of fighters using the airspace if the changes are ultimately approved.