U.S. aviation regulators have approved Amazon's inquiry to test a delivery drone outdoors, as the e-commerce giant pursues its vision of speeding packages to customers through the air. The Federal Aviation Administration (FAA) on Thursday issued an experimental airworthiness certificate to an Amazon unit and its prototype drone design, allowing it to conduct test flights over private, rural land in Washington state.

The FAA also granted Amazon an exemption from general flight restrictions on small unmanned aircraft.

Amazon plans to deliver packages by small, self-piloted aircraft. The company has already been testing several iterations of a drone design at an indoor facility in Seattle.

The experimental certificate applies to a particular drone design. According to the certificate, Amazon must keep flights below 400 feet (120 meters) and keep the drone in sight, according to the FAA. The company had asked for permission to fly at altitudes up to 500 feet (150 meters.)

The drone operators must have a private pilots' license and current medical certification.