Under the FAA Modernization and Reform Act of 2012, Congress directed the FAA to develop guidelines for safely accelerating the integration of drones into the national airspace system by September 2015. Calo said the act was intended to streamline the process by which public and private entities can get licenses to fly drones.
Since 2007, the agency has issued 1,428 certificates of authorization allowing for drone use to police departments, universities and other public bodies. According to the FAA, 327 of those permits were still active as of Feb. 15.
Private companies, such as drone manufacturers, can fly drones for testing, demonstration and training after getting an experimental airworthiness certificate from the FAA.
Hobbyists and recreational users of model aircraft currently don't need any special licensing but are encouraged to follow guidelines that are outlined in a 1981 circular. The guidelines say model aircraft should be operated at a site that is a "sufficient distance from populated areas" and not flown above 400 feet.
Right now, there are no provisions for commercial, for-hire unmanned aircraft operations, but Calo said that's expected to change.
Many states aren't waiting for the federal government to address concerns about privacy. Lawmakers in more than 25 states have proposed legislation related to drone use.
Some cities, fearful of abuse, have banned or considered banning their use by law enforcement. Police in Seattle recently scrapped plans to use two high-tech drones following protests from residents.
In Michigan, McMillin is working on legislation that would prohibit government use of drones except under limited circumstances.
It is based on model legislation created by the American Civil Liberties Union, which says that law enforcement should only use the devices with a warrant or in emergency situations when a person's safety is imminently threatened. The bill also sets parameters on how data is collected, used and retained.
The technology behind drones is evolving quickly, McMillin said.
"I think there's probably going to be legal issues tomorrow that we don't know about today. ... It's uncharted territory, for sure," he said.
A Jan. 30 Congressional Research Service report prepared for members of Congress outlined some of the legal questions.
"Several legal interests are implicated by drone flight over or near private property. Might such a flight constitute a trespass? A nuisance? If conducted by the government, a constitutional taking?" the report asked.
Courts have generally upheld the principle that people do not enjoy a reasonable expectation of privacy in public, even on portions of their own property visible from a public vantage. The Fourth Amendment to the Constitution protects against unreasonable searches and seizures by the government.
An ACLU report about drones says the U.S. Supreme Court has allowed some warrantless aerial surveillance from manned aircraft but has not taken a position on whether the Fourth Amendment limits government use of drone surveillance.
"I think the nexus is this concept of what is public, and what is private?" said Shelli Weisberg, legislative director for the ACLU of Michigan. "Just because you're out in public, does it mean that nothing you're doing is private? Is the conversation with the person you're walking with private? Those are the things that will be (eventually) tested by the courts."
Both Weisberg and Calo said that when it comes to drones, current privacy law is inadequate.
"If the idea (is) that these things are going to follow folks around or patrol a particular neighborhood, there isn't much in American privacy law that stands in the way. That's both on the Constitutional law side and the civil law side," Calo said.
Privacy isn't the only concern.
This week an Italian airline pilot reported spotting a small, black drone hovering just a few hundred feet from his passenger plane as it made a final approach for a landing at New York's JFK Airport.
The pilot reported the drone was flying at about 1,800 feet some 3 miles from the airport, according to various published reports.
Although the plane landed safely, the incident drew the attention of the FAA and counterterrorism officials in New York and at the FBI.
As drone use grows, so do privacy, safety concerns