LONDON — The day seemed to be going well at Gatwick Airport, even if it was bit jittery. After rogue drones forced it to close for 32 hours this week, the airport, one of Europe’s busiest, reopened Friday morning and had a nearly 12-hour uninterrupted run of takeoffs and landings.
Then came an unconfirmed drone sighting, forcing the airport to close yet again, although briefly, leaving planes circling above and travelers fuming in the terminals.
And by the time flights resumed Friday night, all the same questions remained: Who was behind the incursions? Why couldn’t they be stopped? And is Britain doing enough to keep the devices away from airports and other sensitive spots?
Gatwick officials said that unspecified support from the military had provided them with the “reassurance necessary” to reopen the airport’s runway Friday evening. It had been shut from Wednesday night to Friday morning — at the peak of holiday travel, no less — as drones repeatedly buzzed overhead.
But if the military’s more sophisticated detection systems allowed the airport to reopen again Friday night, they are not going to be on hand forever. That left many to wonder not only about future flights at Gatwick, but also about why the British government has not moved more assertively to regulate devices that are widely available and easy to manipulate.
Britain is years behind the United States in requiring drone operators to register with federal authorities, a step that makes it easier for investigators to trace who is behind missteps. British elected leaders said the government should also do more to restrict drones near airports, widening the no-fly zone, which is now one kilometer, or three-fifths of a mile.
“The British government’s approach is that we want to be sympathetic to, hospitable to, the drone industry,” said David Dunn, an expert in international security at the University of Birmingham. “Part of the nervousness, the reluctance in bringing in new regulation is not to kill what they see as a potential golden goose.”
Government ministers said they would hold talks with airports about how to deal with future incidents. But Professor Dunn said he had met with cabinet ministers, spoken to transportation officials and given testimony to parliamentary committees about measures the government should consider — all with little to show for it.
“You try, and it feels like you’re hitting your head against the brick wall,” he said.
On Friday, the police said they had identified “persons of interest” in the drone incursions, but otherwise offered few answers about who was behind them. Nor was it clear what the motivation might have been, beyond the police saying that the incursions were deliberate.
Officials offered few promises about the days ahead.
“I cannot guarantee that another drone isn’t going to pop up and disrupt the airport,” said Assistant Chief Constable Steve Barry of the Sussex Police. Speaking to reporters outside the airport, he said there was “no evidence” that the drone incursions were state-sponsored, adding that they could be the result of “high-end criminal behavior” or “individuals trying to be malicious.”
At least 150 flights were canceled on Friday, causing a ripple effect elsewhere in Europe, after 800 flights had been halted earlier in the week. In all, upward of 100,000 passengers were affected.
The discount airline easyJet said that runway movements had been “restricted to a limited number per hour” and, like other airlines, warned passengers on Friday night to confirm the status of their flight before leaving for the airport. Still, the scene at Gatwick on Friday was much calmer than in previous days, when frustrated and frantic passengers packed its two terminals.
Drone industry executives and aviation experts said the systems at Gatwick, as at many airports, were overmatched for monitoring and warding off drones. The military was likely to have used more sophisticated surveillance equipment, like air defense radars or thermal-imaging devices, said Philip Ingram, a former colonel in British military intelligence.
Those tools could allow investigators to see drones at a much longer range and scan the area where they may have taken off, offering some reassurance that officials would know about them before they arrived over the runway.
It was not clear how big or sophisticated the drones were that flew over Gatwick. The British Civil Aviation Authority said in a report this year that it was “unlikely that a small drone would cause significant damage to a modern turbofan jet engine.”
If Gatwick officials could have monitored the drones’ approach before they reached the airspace over the runway, they may have been able to avoid shutting the airport, said Robert Garbett, the chief executive of Drone Major Group, which consults for companies that operate drones and counterdrone technology.
“It’s like they had a big red switch, and it’s the only switch they had,” Mr. Garbett said.
In the United States, drone operators have had to register with the Federal Aviation Administration since December 2015, though there was a brief period when the rules lapsed because of a court challenge. That created a system of physical identification markers on the devices. Now American aviation officials are developing a virtual license plate that would allow investigators to remotely identify a drone.
Britain has moved more slowly. Not until Nov. 30, 2019, will owners of drones weighing more than 250 grams, or a bit more than half a pound, have to register the devices with the Civil Aviation Authority.
Admiral Lord Alan West, a minister for security and counterterrorism from 2007 to 2010, said he had warned for years, starting when he helped plan security measures for the 2012 Olympics in London, of the threat from rogue drone operators. But he said part of the reason for the government’s slow response was lobbying from drone manufacturers.
Lord West said terrorist groups were already beginning to use drones, and there were risks of operators replacing the cameras on drones with explosive devices.
“I don’t think the government is taking these things seriously enough,” he said. “I think they were slow in reacting.”
Chris Grayling, Britain’s transportation minister, acknowledged in an interview with the BBC on Friday that the government needed to pick up the pace of preparations. “We’re going to have to learn very quickly from what’s happened,” Mr. Grayling said, referring to the rogue drone breaching Gatwick Airport, an episode he described as “unprecedented, anywhere in the world.”