New findings shed light on drone encounters

The peer-reviewed paper published in the SAE International Journal of Aerospace was a collaborative effort by SAE International, Embry-Riddle Aeronautical University, and Unmanned Robotic Systems Analysis. The team analyzed more than 1.8 million piloted aircraft operations and nearly 460,000 flights by small uncrewed aircraft (sUAS) around Dallas-Fort Worth International Airport between August 2018 and July 2021. They identified 24 near-midair collisions, defined as aircraft (of each variety) operating within 500 feet of each other. Most of these close calls took place within 1.5 miles of a runway, and the research team recommended expanding drone exclusion zones (established electronically in the most popular brand, and others) around runways from about 1 mile to 3.5 miles.

“That modification would provide enhanced protection for piloted aircraft operating at less than 500 feet above ground level during approach or departure,” said Ryan Wallace, ERAU associate professor of aeronautical science. “Typically, small uncrewed aircraft don’t fly above 400 feet.”

In the decade since easy-to-fly drones made for consumers without any aeronautical experience became widely available in big-box retail stores, their numbers have boomed. The FAA estimates 2.4 million sUAS will have been sold by 2025, up from 1.46 million in 2020.

“The proliferation of drones, particularly ones available to the general public, poses obvious risks,” said research collaborator and ERAU Professor of Human Factors Stephen Rice, in a news release. “Unfortunately, not all drone operators are responsible, knowledgeable or safety-minded. Many of them are not even aware of the rules they must follow.”

Concern among pilots and the FAA has combined with uncertainty, with thousands of pilots reporting drone encounters at a range of altitudes and phases of flight, that could rarely be corroborated objectively. The new study is the first to analyze data, not rely on eyewitness accounts, and found that three specific sUAS were involved in more than half (13) of the 24 encounters documented in the data. In all but one of the 24, the drone was operated above the altitude limit sUAS are required to abide by (400 feet agl, or within 400 feet of any structure).

The authors note that a handful of actual collisions have been documented, though they remain rare. They expect implementation of the remote identification (RID) rule in September, when most drones operated outside of designated areas will be required to broadcast a "digital license plate" at all times. "RID signals should further enhance objective information about near-miss encounters between drones and airplanes," Wallace said.

The 24 close-call events included two in 2018, one in 2019, 14 in 2020, and seven in 2021, the researchers reported. The mean lateral distance between the drone and the crewed aircraft was about 215 feet. Commercial air carriers were involved in 11, another seven involved helicopters, and six involved general aviation aircraft. "All of the helicopter encounters happened within 1.25 miles of a heliport," the researchers noted in a press release. "Similarly, in 10 of the 11 air carrier encounters, the aircraft was within 1.5 miles of approach or departure and lower than 500 feet above the ground."