Pilots approaching a runway usually can’t see small unmanned aircraft systems (sUAS) encroaching on their airspace, and they virtually never detect motionless drones, according to a recently published study. During an airborne human factors experiment, pilots in a Cessna 172S failed to see a common type of quadcopter in motion during 28 of 40 close encounters, researchers with Oklahoma State University and Embry-Riddle Aeronautical University reported.

The pilots got a bead on the invading drone in only 12 out of the 40 cases, or about 30 percent of the time. When the drone was not moving, the task became even more difficult. A mere three out of 22 motionless drones were spotted by the pilots. Drones were detected at distances of between 213 and 2,324 feet. If a drone was identified at the study’s maximum detection range of 2,324 feet, the pilot would have about 21 seconds to avoid a collision, according to the research.

While the FAA “has made strides to secure control airspace from sUAS incursions,” the study authors wrote, “their efforts have been met with mixed results.” There is currently no reliable method for tracking sUAS flights within the U.S. The research team’s next project will involve rigging a drone with ADS-B technology to track it. This study will assess whether the technology helps pilots pinpoint and avoid the drone.