London airport open, but location of drone culprit up in air

London airport open, but location of drone culprit up in air
A plane comes in to land at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth) (Source: Kirsty Wigglesworth)

LONDON (AP) — London's Gatwick Airport operated without problems Sunday, but the fugitive drone operators who brought incoming and outgoing flights to a standstill over multiple days remained at large — and a potential threat — after police cleared two local residents who were arrested as suspects.

Sussex Police were hopeful they had halted the disruptive and costly drone incursions during one of the heaviest travel periods of the year with Friday's arrests of a couple who live near the airport. But they were released Sunday, and police said they were no longer suspects.

Tens of thousands of passengers suffered through long flight delays or were stranded by cancellations after two drones were reported seen above the airfield at Gatwick on Wednesday night, prompting an immediate suspension of all air traffic.

Sussex Chief Detective Jason Tingley said Sunday he could not rule out new drone activity at Gatwick or other U.K. airports. He also said it was possible that witnesses who reported sightings after the first ones aroused alarm were mistaken.

"Of course, that's a possibility. We are working with human beings saying they have seen something," Tingley told the BBC.

A plane comes in to land at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth)
A plane comes in to land at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth) (Source: Kirsty Wigglesworth)

At the same, he said police were making progress in a three-pronged investigation: tracking "persons of interest," investigating 67 reported drone sightings, and examining a damaged drone found near Gatwick.

The drone in police hands may provide useful forensic clues, such as the DNA of people who handled it, Tingley said. But the rain the London area got on Friday and Saturday might have washed away some evidence, he said.

Passengers queue for flights at Gatwick Airport as the airport and airlines work to clear the backlog of flights delayed by a drone incident earlier in the week, in Crawley, England, Saturday, Dec. 22, 2018. London's Gatwick Airport took strides toward running a full schedule Saturday as police questioned a man and a woman in connection with the drone intrusions that caused mayhem for tens of thousands of holiday travelers. (Gareth Fuller/PA via AP)
Passengers queue for flights at Gatwick Airport as the airport and airlines work to clear the backlog of flights delayed by a drone incident earlier in the week, in Crawley, England, Saturday, Dec. 22, 2018. London's Gatwick Airport took strides toward running a full schedule Saturday as police questioned a man and a woman in connection with the drone intrusions that caused mayhem for tens of thousands of holiday travelers. (Gareth Fuller/PA via AP) (Source: Gareth Fuller)

Airport authorities consider drones a menace because they could damage a plane in flight or be sucked into a plane's engine, causing a deadly crash

After the shutdown extended into Thursday, increased military protection was brought in Thursday night to watch for more drones while planes resumed taking off and landing at Britain's second-busiest airport.

Passengers queue for flights at Gatwick Airport as the airport and airlines work to clear the backlog of flights delayed by a drone incident earlier in the week, in Crawley, England, Saturday, Dec. 22, 2018. London's Gatwick Airport took strides toward running a full schedule Saturday as police questioned a man and a woman in connection with the drone intrusions that caused mayhem for tens of thousands of holiday travelers. (Gareth Fuller/PA via AP)
Passengers queue for flights at Gatwick Airport as the airport and airlines work to clear the backlog of flights delayed by a drone incident earlier in the week, in Crawley, England, Saturday, Dec. 22, 2018. London's Gatwick Airport took strides toward running a full schedule Saturday as police questioned a man and a woman in connection with the drone intrusions that caused mayhem for tens of thousands of holiday travelers. (Gareth Fuller/PA via AP) (Source: Gareth Fuller)

The government has kept the details of the security operation secret, but the military equipment is thought to offer better tracking capabilities and give authorities early warning if drones approach Gatwick, located 30 miles (45 kilometers) south of London.

At the airport on Sunday, flight arrival and departure boards showed fewer delays than on Saturday. Additional tracking gear at the periphery of the runway and an increased police presence were the only clear signs of the headaches experienced there in the past four days. But officials have stepped up surveillance of the surrounding airspace behind-the-scenes.

Passengers at Gatwick airport waiting for their flights following the delays and cancellations brought on by drone sightings near the airfield, in London, Friday Dec. 21, 2018. New drone sightings Friday caused fresh chaos for holiday travelers at London's Gatwick Airport. (John Stillwell/PA via AP)
Passengers at Gatwick airport waiting for their flights following the delays and cancellations brought on by drone sightings near the airfield, in London, Friday Dec. 21, 2018. New drone sightings Friday caused fresh chaos for holiday travelers at London's Gatwick Airport. (John Stillwell/PA via AP) (Source: Isabel Infantes)

British Transport Secretary Chris Grayling has said the unspecified "military measures" have bolstered confidence that the airport will be able to remain open without further interruptions. But anti-drone technology is a relatively new, imperfect field, Grayling said.

It is not clear how officials will respond if another drone gets too close. The best guide may be what happened on Friday night, when the airport was shut down for 70 minutes after a drone was spotted. The military deployment allowed the airport to reopen relatively quickly, authorities have said.

A plane comes in to land at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth)
A plane comes in to land at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth) (Source: Kirsty Wigglesworth)

No confirmed drone incursions have taken place since then — a factor that led many to assume police had found the responsible operators when they arrested the two suspects Friday night.

That hope ended Sunday when the couple — a 47-year-old man and a 54-year-old woman — was allowed to return to their home in Crawley, a 5-minute drive from Gatwick.

Passengers wait to check in at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth)
Passengers wait to check in at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth) (Source: Kirsty Wigglesworth)

Detective Tingley said he is satisfied the two were not involved. He is hoping a tip will provide a crucial lead.

Tingley said police did not identify the suspects but The Mail on Sunday tabloid named them and published a large front-page photo of them with the headline, "Are These the Morons Who Ruined Christmas?"

A passenger checks an arrivals board at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth)
A passenger checks an arrivals board at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth) (Source: Kirsty Wigglesworth)

The crisis at Gatwick marked the first time drones caused sustained disruption at a major airport. There is not much data on the dangers drones pose to airplanes because they are a relatively new phenomenon.

Police say the motive for the drone incursion is not yet known but they do not believe it is "terror-related."

Passengers wait to check in at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth)
Passengers wait to check in at Gatwick Airport in England, Friday, Dec. 21, 2018. Flights resumed at London's Gatwick Airport on Friday morning after drones sparked the shutdown of the airfield for more than 24 hours, leaving tens of thousands of passengers stranded or delayed during the busy holiday season.(AP Photo/Kirsty Wigglesworth) (Source: Kirsty Wigglesworth)

Gatwick Airport, which handles roughly 43 million passengers per year, has offered a 50,000 pound ($63,000) reward through Crimestoppers for information leading to the arrest and conviction of the drone operators.