Illegal drone operators are flying under the radar.

Since 2016, when the Federal Aviation Administration began requiring commercial drone pilots to obtain a license, the agency has only busted a single pilot for operating illegally — and even he got off with a gentle slap on the wrist, according to FOIA documents obtained by MarketWatch.

Last year, Jeffrey Slentz was caught by a cop flying a drone over Kauffman Stadium in Kansas City, Mo., for a music video.

The officer reported him to the FBI and FAA — but all Slentz received was a warning letter telling him to obtain a drone pilot’s license.

Three other licensed pilots who violated FAA rules have been given warning letters or told to take a safety course at a local Flight Standards District Office, MarketWatch reported.

Some licensed pilots are upset that illegal operators are getting off easy.

“It’s annoying that other drone businesses are operating without a license and I have no competitive advantage,” said Flo Minton, a Florida-based photographer.

“I went through all this trouble to pass the test to get my license, including paying for a study course and the test fee, and it took me weeks to study.”

Another drone pilot, Daniel Carnahan, said he’s reached out to the Kansas City Flight Standards Office three times to report a pilot who’s been breaking licensing rules, called Part 107. He believes that pilot has gone unpunished.

“I know tons of people who fly at night, who operate from a moving vehicle,” Carnahan told MarketWatch.

An FAA spokesman said state and local law enforcement “are often in the best position to deter, detect, immediately investigate, and, as appropriate, pursue enforcement actions to stop unauthorized or unsafe UAS operations.”

Drones have posed problems in the Big Apple and beyond in recent years.

In September, a drone illegally flying over a residential neighborhood in Staten Island struck an Army chopper, damaging its rotor blades.