For about 90 minutes on Tuesday night, air traffic at Newark Liberty International Airport in New Jersey was suspended after two pilots reported seeing drones in nearby airspace.
Such disruption at one of America's busiest airports follows the drone-related chaos that interrupted service at London's Gatwick Airport at the height of last month's holiday rush — events that could signal a new and regularly occurring headache for air travelers, aviation and drone experts warn.
The recent commotion set off a chain reaction of delays: More than 40 flights were held for an average of 21 minutes during the incident at Newark, federal aviation officials said Wednesday. Dozens of other planes were left circling, including a United Airlines flight from Jamaica just minutes away from running out of fuel.
One pilot told air traffic control that the object in the skies "definitely looks like a drone," and it came "about 30 feet away from the right wing."
Irresponsible drone use near airports will "put unnecessary stress on our pilots and controllers teams, while causing concerns for passengers," said Javid Bayandor, an aerospace engineer and professor who runs the CRASH Lab at the University at Buffalo, which studies drone strikes.
An airplane's wings, engines, vertical stabilizer and windshield are most susceptible to being harmed by an unmanned aircraft.
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Drones that weigh 10 to 15 pounds "could do a significant amount of damage to an airplane, and if it were close to the ground, it could result in loss of the airplane," John Cox, a retired airline captain and aviation analyst, previously told NBC News. "The drone threat is very, very real."
While it remains rare to shut down airport operations because of a drone, pilots last year reported at least 2,000 drone sightings in the U.S. through October, according to the Federal Aviation Administration.
And drones continue to grow in popularity, with about 1 million of them registered with the federal government, mostly by hobbyists, with that number expected to more than double by 2022.
The FAA's guidelines say that drones must stay at least five miles away from an airport, unless they receive permission from the agency, while remaining below an altitude of 400 feet.
The drones reported Tuesday near Newark airport were flying at 3,500 feet. In recent years, there have been instances of drones flying in airspace where wildfires in California were being fought and nearly hitting a medical helicopter taking off in Dallas.
Experts say drones are flown near airports or might flout the law regularly, they're just not always seen.
A study by the Embry-Riddle Aeronautical University with the help of FLYMOTION, a Florida-based drone technology firm, found that 192 drone flights were conducted close to the Daytona Beach International Airport over a 13-day period in 2018. Most notably, one in five of them posed a risk to an airplane.
"It's critical to the safety of everybody that drones are operated responsibly," said Ryan English, the CEO and co-founder of FLYMOTION.
He added that airports need to start looking at drone-detection technology as another form of security for keeping flights safe.
Many consumer drones also come with technologies that can prevent them from flying too close to restricted air spaces, such as near an airport or stadium, by using GPS-based software that creates virtual fences.
DJI, a global drone manufacturer, includes such technology with its drones.
Adam Lisberg, a company spokesman, said he's not sure it was a drone that was seen near Newark airport, and the dark conditions and the cold weather wouldn't be ideal for flying. Even with the incident at Gatwick, British police have not confirmed drones were involved and police later released two people without charge.
"Back in the 1970s, UFOs were a big thing, and suddenly everyone was seeing a UFO," Lisberg said. "Even a well-intentioned airline pilot could miss accurately identifying something the size of a dinner plate at 3,500 feet in the air."
Regardless of whether drones were involved in the latest incidents, English said, airports, manufacturers and government agencies will need to work together to ensure there's a clear pathway for operating them.
"Disruptions caused by drones don't have to happen," he added. "It doesn't have to be another headache for air travel if we don't let it."