By Billy Perrigo
Updated: December 20, 2018 7:33 AM ET

A shutdown at the U.K.’s second-busiest airport is expected to continue into a third day after two drones were spotted over the runway.

Gatwick Airport Chief Executive Officer Stewart Wingate released a statement Thursday night apologizing for the airport’s shutdown and said he is working with authorities to bring down the remotely-piloted vehicles down over the airport, which is 25 miles outside London.

Gatwick was closed all day Thursday and the shutdown is expected to continue into Friday, Wingate said.

More than 10,000 passengers have been affected, with some flights having to be diverted as far afield as Paris and Amsterdam.

The drones were first spotted at 9 p.m. on Wednesday night, causing the runway to be shut until around 3 a.m. Then, 45 minutes later, the drones were spotted again and the runway closed for a second time.

Who is piloting the drones?

The authorities don’t know. Police were combing the surrounding areas overnight and into Thursday morning in an attempt to catch the operators.

“Each time we believe we get close to the operator the drone disappears,” Justin Burtenshaw, the official in charge of the operation, told the BBC. “When we look to reopen the airfield, the drone reappears, so I’m absolutely convinced it is a deliberate act to disrupt Gatwick airport.”

“There has been no intelligence that this is going to happen. This is just a random act that has happened overnight,” he said.

Could the incident be terror-related?

Although the drones have caused major disruption to airlines, local police said on Thursday that there were no indications the incident was terror-related.

However, at least one drone enthusiast suggested on Twitter the culprits were unlikely to be amateur pilots, pointing to the rainy and windy conditions, and the low battery life of civilian drone technology:

But one drone expert poured cold water on that theory. “This is likely to be a shop-bought drone,” Rupert Dent, a spokesperson for the Association of Remotely-Piloted Aircraft Systems, told TIME. “The reports suggest there are multiple drones, sighted at different times. They’re not necessarily in the air for extended periods of time.”

In a statement, the airport said: “There is significant disruption at Gatwick today as a result of what appears to be a deliberate attempt to disrupt flights.”

Why can’t police shoot the drones down?

Airport officials said police had advised shooting the drones down would be too dangerous, because of the risk of stray bullets falling to earth.

How else could the drones be brought down?

Aside from apprehending the operators from the ground, there are several ways police might be able to take the drones out of action.

Technology exists that can jam the wireless communications between the operator and the drone, although this could have unanticipated side-effects in an airport environment.

And a new large, autonomous drone called the “DroneHunter” is able to catch smaller drones by dropping a giant net onto them.

Sussex police did not immediately respond to a TIME request for comment about what options were available to them.

What penalties might the operators face if caught?

Flying drones over restricted territory such as airports is a criminal offense in the U.K.

The U.K.’s aviation minister said on Thursday morning that the culprits could face up to five years behind bars if caught and convicted.

There also may be legal grounds for airlines or insurance companies to sue the perpetrators for loss of income.

Are drones really that dangerous for planes?

Airplane engines are designed to be able to survive flying through flocks of birds, though such incidents have brought down passenger aircraft before.

But drones could pose an even greater risk to planes, according to a study from December last year, due to their makeup of metal and dangerous components, like lithium from batteries, which can cause explosions.

Write to Billy Perrigo at billy.perrigo@time.com.

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