The FBI is investigating reports that a "guy in a jetpack" was seen by pilots flying near Los Angeles' LAX airport nearby to where planes were landing.
The incident, which was recorded by air traffic controllers, happened on Sunday evening and was witnessed by pilots on two separate planes.
The apparent culprit was seen flying at an elevation of 3,000ft (915m).
Jetpacks, once the realm of science fiction, have become a thing of reality in recent years, according to experts.
"Tower, American 1997 - we just passed a guy in a jetpack," the pilot of American Airlines flight 1997 from Philadelphia told officials in the control tower as he approached LAX around 18:30 local time (01:30 GMT).
"Were they off to your left side or right side?" the controller responds, leading the pilot to say the person was 300 yards to the plane's left.
Within a minute, a pilot flying JetBlue Flight 23 also reported seeing a man fly past. As the controller advised the pilot to be cautious, he added "Only in LA", according to LiveATC.net, which records air-traffic control transmissions.
The FBI and the Federal Aviation Administration are both investigating the incident.
Inventors around the world have constructed jetpacks in the past decade, with one man in Brighton, in the UK, recently breaking the speed record after travelling at a rate of 85.06 mph (136.89km/h).
They have been used to fly around Dubai and the Statue of Liberty in New York City.
JetPack Aviation, based in the San Fernando Valley region of Los Angeles, boasts of being able to fly a person to 15,000ft, but the owner of the company told the LA Times on Tuesday that their product is not available for private use.
David Mayman, the chief executive of the company, speculated that someone may have been working on a secret project and just revealed it over the weekend. Or it could have been a mannequin strapped to a drone, he suggested.