“You don’t hear that every day,” a JetBlue pilot said. “Only in L.A.”

There is a mystery unfolding in Los Angeles. It wasn’t Buzz Lightyear or Robert Downey Jr. in “Iron Man,” but pilots landing at Los Angeles International Airport on Sunday evening reported seeing a man wearing a jetpack flying near their planes.

American Airlines flight 1997 from Philadelphia to L.A. was the first to report in.

“Tower, American 1997, we just passed a guy in a jetpack,” the American Airlines pilot radioed to air traffic control, according to recordings by LiveATC.net.

Air traffic controllers sounded stunned in response and asked the pilot for more details.

“American 1997… Okay…. Were they off to your left side or right side?” the controller asked.

The pilot said the man was flying with a jetpack at 3,000 feet and only about 300 yards away from the plane, Airbus A321.

Shortly after that, another pilot reported that he, too, saw a man in a jetpack flying near their plane.

“We just saw the guy passing by us in the jetpack,” the SkyWest pilot told controllers.

Other aircraft were then immediately warned to use caution because of a man wearing a jetpack flying in the path of planes.

“You don’t hear that every day,” a JetBlue pilot said. “Only in L.A.”

The Federal Aviation Administration (FAA) said that the report was turned over to the Los Angeles Police. Authorities have not found any man with a jetpack, and who or what came close to the plane remains a mystery. The FAA says an investigation is underway.

According to the FAA, reports of unmanned aircraft sightings from pilots, law enforcement personnel and the general public have increased dramatically over the past two years. The agency says it receives more than 100 such reports each month. If, in fact, the sighting was of a man with a jetpack, it would have been illegal for him to fly in commercial airline airspace or to fly alongside planes.

There are some human jetpacks in development that can reach altitudes of up to 12,000 feet with price tags of a half-million dollars.

“The size, weight of a person in a jet pack impacting an airplane at the exact wrong spot could potentially bring that airliner down,” ABC News Contributor and retired Marine Col. Steve Ganyard said. “This is why it’s so important for when these technologies come along — drones, jetpacks, taxis in the sky — that people need to fly them in a responsible way and not put the flying public in danger.”

An FBI spokesperson told ABC News “the FBI is aware of the reports by pilots on Sunday and is working to determine what occurred.”

ABC News’ Luke Barr and Amanda Maile contributed to this report.