A gyrocopter sits on the West Lawn of the U.S. Capitol with members of the U.S. Capitol Police nearby. (Photo by Alex Wong/Getty Images)

They might not have known what exactly the flying contraption was, but bystanders who witnessed a mailman’s gyrocopter flight to the U.S. Capitol knew it definitely wasn’t a kite, balloon, or flock of birds.

On a radar screen, though, a gyrocopter is nearly indistinguishable from such flying objects, FAA and NORAD officials said at a House committee hearing on Wednesday.

In testimony before the House Committee on Oversight and Government Reform Wednesday, FAA administrator Michael Huerta explained that air traffic controllers use a radar feed that filters out non-aircraft objects.

“Air traffic controllers could not do their jobs if they had to work with an unfiltered radar feed. They would not be able to distinguish the aircraft they are charged with safely handling from the other elements on their radar scopes,” he said.

But even when looking at the full screen—which might include things like weather events, migrating birds, and balloons—pinpointing a gyrocopter isn’t an easy task. “Identifying low altitude and slow speed aerial vehicles from other objects is a technical and operational challenge,” Adm. William Gortney, chief of the North American Aerospace Defense Command, said in his testimony.

When analysts went back after the evident, they learned that the gyrocopter was indeed “detected by several of the integrated sensors as it approached and transited through the SFRA,” Gortney said. But he added that “the aircraft’s flight parameters fell below the threshold necessary to differentiate aircraft from weather, terrain, birds, and other slow flying objects so as to ensure that the systems and those operating them focus on that which poses the greatest threat.”

Huerta explained:

After the incident, we conducted a forensic radar analysis and looked for a symbol that might match Mr. Hughes’ gyrocopter. We understood he had taken off from a small airport in Gettysburg, Pennsylvania, and we had an approximate time, so we looked at unfiltered radar data. A trained radar analyst identified a slow-moving symbol that traveled from Gettysburg toward the Capitol, and vanished from radar at about the time Mr. Hughes landed on the West Lawn. We now believe that unidentified radar element was Mr. Hughes’ gyrocopter. The dot appeared only intermittently throughout the flight.

In addition to beefed up security, Homeland Security Secretary Jeh Johnson said the penalties for such a flight—Hughes is facing four years in prison—should be much stiffer, ABC reported. Hughes’ actions “constitutes a threat to public safety, not just to the intruder but to those on the ground,” Johnson said in a separate hearing.