Preheat the oven to 350 degrees F. Season the pork chops with salt and pepper, and then coat in flour shaking off excess. Heat the oil in large non-stick skillet over medium-high heat. Brown the pork chops and then place in casserole dish. Add the onion and celery to the skillet and cook, stirring occasionally, until softened, about 3-4 minutes. Stir in the cider, sage and cider vinegar. Bring to a boil, and then pour over the pork chops. Cover and bake pork chops 1 hour, or until tender. Serve the pork chops with the braising liquid spooned over the top.