March 20, 2015 1:35 PM, EDT

FAA Grants Amazon Experimental Permit for Drone Test Flights got a boost from U.S. regulators who granted the company permission to conduct test flights in its effort to expand research into the viability of delivery drones.

Amazon wrote to the Federal Aviation Administration in December threatening to divert its research program to other countries if the agency didn’t act quickly to approve outdoor test flights of the unmanned aircraft.

The FAA ruled March 19 said Amazon can fly its drones only during the day, within 400 feet of the ground and within sight of an operator who has a traditional pilot’s license.

It’s not clear when or if the FAA will create blanket rules for allowing the kind of autonomous drone flights envisioned by Amazon CEO Jeff Bezos. The Seattle-based company has said it wants to be able to program the unmanned aircraft to make the flight, while dodging obstacles, on its own.

The FAA granted Amazon what is known as an experimental airworthiness certificate for its drone design, which is broader than the waivers given to at least 44 other companies for commercial drone flights. By approving the aircraft’s design, the FAA can allow a greater range of flights than a simple commercial waiver.

Bezos said in December 2013 that he wanted to pioneer the use of small unmanned copters to deliver books and other items to people’s homes, with a goal of delivering packages weighing as much as 5 pounds within a 10-mile radius.

The FAA last month unveiled proposed rules for commercial drone flights that would not permit such automated activity because it requires drone operators to keep their craft within sight at all times.