Doyle Rice

USA TODAY

What happens if a drone hits you in the head?

The Federal Aviation Administration (FAA) wants to know, so they conducted a study to understand and mitigate the risks of drones flying over people, and what happens if a drone loses connection to its pilot or just crashes to the ground.

It turns out that small drones are safer near people than was thought.

"We were able to identify blunt force trauma, penetration injuries and lacerations as the most significant threats to people on the ground,” said David Arterburn, an engineer at the University of Alabama in Huntsville and lead investigator for the study, which was conducted by several universities and released Friday afternoon in Washington, D.C.

As part of the test, the researchers dropped a typical drone (a Phantom 3, weighing 2.7 pounds) on a crash test dummy at a typical speed of about 34 mph. They found that while there was only a 0.01 to 0.03% chance of a serious head injury, there was an 11-13% chance of a serious neck injury.

The team classified collision severity by identifying hazardous drone features, such as unprotected rotors.

Some good news out of the study was that multi-rotor drones fall more slowly, due to aerodynamic drag, and cause less damage than the same mass of metal or wood. Drones also deform and flex more than wood and metal debris, imparting lesser amounts of energy and, therefore, less damage.

As for potential fatalities, blunt force trauma would be the most significant contributor, the study found. For lacerations, the report said that protective blade and rotor guards should be required for all flights over people.

Flying over people not associated with the flight is one key to deliveries and other urban uses of drones.

“The results of this work are critical to the successful commercial operations of flying unmanned aircraft over people and beyond the pilot’s visual line of sight,” said Mississippi State University’s Marty Rogers, director of the FAA's Alliance for System Safety of Unmanned Aircraft Systems through Research Excellence (ASSURE).

UAS is the industry acronym for drones, which are aircraft flown remotely without a human pilot on board.

The next phase of the research will begin in June 2017, and will verify the findings of this study, as well as develop tests that manufacturers can use to certify their drones for flights over people.