An appeals court on Friday struck down a Federal Aviation Administration rule that required owners of drones used for recreation to register their craft. The ruling was a victory for hobbyists and a setback for the FAA, which cited safety concerns as it tried to tighten regulation of the fast-growing army of drone operators. Some pilots of commercial airliners have reported close calls with drones flying near airports. About 760,000 hobbyists have registered more than 1.6 million drones since 2015, and sales have skyrocketed. The FAA estimates that hobbyists will buy 2.3 million drones this year and 13 million by the end of 2020.