GPS is not approved by the FAA for what? While it is not approved to be the sole naviagtion system in aircraft, many GPS units are certified for IFR flight in the US. Further, while certification for GPS use by an air carrier is hard to come by, it does happen. For example, a friend of mine is currently in an extended training session in Dallas to learn the GPS that American Eagle's San Juan ATR fleet uses. Most Eagle pilots don't go through this training, but those who will be SJU based ATR pilots must.