Amazon’s drone delivery program faces the challenge of getting drones near enough to large population centers, but the company just filed a patent application for a solution. What Amazon calls “multi-level fulfillment centers for unmanned aerial vehicles” would place drones in the midst of cities in vertical structures, thereby letting drones fly in and out of the building while avoiding pedestrians. Although this idea would solve one problem, it raises others pursuant to drones flying in the sky above a city.

The Verge asks some of those questions: “Who’s going to want to live near a drone delivery tower if it makes so much noise? And what if drones start falling out the sky, making impromptu, and possibly fatal, deliveries?”

As part of the “same round of patent applications as the delivery beehive,” Amazon attempts to address some of those questions, suggesting custom rotors that would break up airflow to create a quieter flight. The application includes an image that shows “trailing edge fringes,” which look like “tiny plant-like fronds,” added to the rotor blades.

The patent application also describes drones with “multiple sets of rotors and motors, so that if one set fails, the other can take over.”

Bloomberg reports on proposed aviation legislation’s impact on Amazon’s drone delivery service. One such provision of the “bipartisan Senate legislation” would “reauthorize the Federal Aviation Administration [to direct] the Department of Transportation to create a carrier certificate allowing for package deliveries by drones.”

Alphabet is also “racing to develop drones capable of delivering parcels to customers,” although, in December last year, Amazon made the first-ever drone delivery, in the U.K.

Regarding the proposed legislation, the Commercial Drone Alliance, which “represents companies that want to use drones commercially, including Time Warner’s CNN,” stated on its website that it was “pleased that provisions intended to expand commercial drone operations have been included” in the bill.

FAA regulations currently “restrict most drone flights directly over people,” but “establishing an air carrier certificate for drone deliveries would clear one hurdle for package delivery.”