LONDON: Thousands of weary passengers remain stranded at Gatwick airport , the UK 's second busiest, for the second day on Friday as the Army was called in to help deal with the unprecedented crisis caused by drones, ahead of the busy holiday season.As the airport resumed operations, British transport secretary Chris Grayling said there was no evidence it was terror-related.By Thursday night, 120,000 people had their flights cancelled, the BBC reported.Gatwick authorities said 765 flights were scheduled for departure and arrival on Friday.Gatwick's chief operating officer Chris Woodroofe said police had not yet found the drone operator. Police said it was possible they were an environmental activist.He said extra "mitigating measures" from the government and military had given him "confidence to reopen" the airport.The airport is expected to be "back to normal" by the end of Saturday, media reports said."We are now operating at almost normal runway conditions and the challenge for the airlines, as the result of this disruption, is that their planes are not all in the right place," Woodroofe said."So what we'll be doing today is recovering their operations so by tomorrow (Saturday) we are back to standard operation and continue to recover the situation for our passengers."The UK's Civil Aviation Authority has said passengers were not entitled to compensation due to the extraordinary circumstances.Grayling said he would talk to the insurance industry and hoped it would take an "enlightened view" on passengers' claims.Police continue their search for those responsible for the chaos, which started on Wednesday night. The airport could not operate while the drones were in flight in case they hit and damaged a plane.Officers have so far failed to locate the "industrial specification" drones or their pilot and had been considering plans to shoot a device down.But Steve Barry, assistant chief constable at Sussex Police , said they were in a "much better position today".He said there were a "number of lines of inquiry" into the "very malicious and criminal behaviour", including the possibility it could have been the work of an environmental activist.Barry said a drone had last been seen at on Thursday night.Gatwick boss Grayling called it a type of disruption "we've not seen before" and "lessons need to be learned".He said the situation was "unprecedented, anywhere in the world"."Every possible measure will be put in place to make sure this can't happen again," he said.But he added there was "no simple solution" and "you can't fire weapons haphazardly around an airport".Gatwick said the flights planned for Friday would have about 126,000 passengers on board. About 140 flights have been cancelled.Woodroofe added: "My intention is to get those passengers to their destinations so that they can enjoy their Christmas."As the West Sussex airport announced the reopening of its runway on Friday, some travellers were hopeful of getting airborne.But others expressed concern that the operators of the drone had not yet been apprehended - and could go on to cause more havoc.All weary travellers could do was monitor the arrival and departure boards - showing many cancellations and delays to flights - and hope their Christmas getaways would not be ruined.The first flights in and out of Gatwick were Norwegian Air, Easyjet and BA departures and a China Eastern Airlines arrival from Shanghai.Gatwick continues to advise passengers to check their flight status before turning up at the airport.Gatwick's runway closed just on Wednesday night when two drones were spotted flying over the perimeter fence and into the airfield.It briefly reopened at early on Thursday but was closed again about 45 minutes later due to further sightings. Outbound flights were grounded, while incoming planes were redirected to other airports.Over 20 police units from two forces joined the search for the perpetrator, who could face up to five years in jail.The military, with "a range of unique capabilities", was deployed to assist the police operation.Superintendent Justin Burtenshaw, head of armed policing for Sussex and Surrey, said finding the drone's operator was "a difficult and challenging" prospect.It is illegal to fly a drone within 1km of an airport or airfield boundary and flying above 400ft - which increases the risk of a collision with a manned aircraft - is also banned.Endangering the safety of an aircraft is a criminal offence which can carry a prison sentence of five years.The number of aircraft incidents involving drones has grown dramatically in the past few years, as the popularity of the devices has increased.In 2013 there were zero incidents, compared to almost 100 last year.Pilots' unions and aviation bodies in the UK have called for tougher measures and immediate action against drone-flying, including wider exclusion zones around airports.