Southwest Airlines, the largest operator of Boeing 737 aircraft, does not have all its fleet ETOPS certified. The Dallas-based airline operates over 800 aircraft but has only a portion certified for Extended Range Twin Operations (ETOPS). This certification allows aircraft to fly routes up to 180 minutes away from an adequate diversion airport with one engine inoperative.
Southwest's network primarily spans the United States, but recent expansions include routes to Hawaii and Costa Rica. These require ETOPS certification due to the necessity of flying over large bodies of water. The Boeing 737 MAX 8, which is ETOPS-180 certified, is typically deployed on these routes.
The Federal Aviation Administration (FAA) regulates ETOPS operations. According to FAA regulations: "An acceptable means but not the only means for obtaining approval under FAR Section 121.161 for two-engine airplanes to operate over a route that contains a point farther than one hour flying time at the normal one-engine inoperative cruise speed (in still air) from an adequate airport."