A no-fly zone is a geographic location over which aircraft cannot fly. These aircraft can include manned aircraft, unmanned aircraft systems (drones) or both. Depending on the area and the specific regulations, this can be for military, security, safety or privacy reasons.
No-fly zones that prohibit manned aircraft use in a military context, but areas that prohibit drones have more complicated rules and are more common. The U.S. Federal Aviation Administration (FAA)'s Small Unmanned Aircraft Rule Part 107 lays out these rules. When used for recreation, drones cannot be flown above 400 feet in highly populated areas and must stay within the line of sight of the pilot. Drones also cannot be flown over sporting events and stadiums during the time starting one hour before and ending one hour after an event. Also, drones cannot be flown fly within five miles of an airport without giving the airport advanced notice, to prevent potential crashes.
Drones used for business purposes are further restricted. In addition to the rules regarding drones flown for recreation, they may only be flown within Class G airspace, or completely uncontrolled airspace, and cannot fly over people. If a drone must break these rules to complete the business purpose it is being used for, the organization overseeing it must apply for a waiver of these regulations from the FAA.
There are other Special Flight Rules Areas (SFRAs) which have other restrictions on drone use. For example, Washington, D.C. has its own flight rules: No drones may fly within a 15-mile radius of Ronald Reagan Washington National Airport, and outside of that, only drones weighing less than 55 lbs may fly within a 30-mile radius of the airport. Other restricted areas include military bases and national parks, and depending on state laws can include prisons, hospitals or other buildings. Temporarily restricted areas can include emergency response areas, such as wildfires, and the area where the president of the United States is if he or she is traveling.
Some drone manufacturers use geofencing technology to enforce no-fly zones. In this case, the drone uses GPS technology to track its location, and if it reaches the boundary of a no-fly zone, it will stop or send the pilot an alert, depending on the manufacturer's settings. However, not all drone manufacturers use the same rules to determine what areas are geofenced, so some drones may be able to fly where others are not.