At about 9 pm on 19 December 2018, a security officer going off duty reported sighting two drones in the vicinity of Gatwick Airport, London. He claimed one drone was hovering over a carpark, while the other crossed the security fence. He called the Gatwick Control Centre.

The runway was immediately closed. Within half an hour, six more sighting reports came in, including five from police officers. Over the next two days, as the airport struggled to resume operations, more sightings occurred. Each time the runway was about to open, somebody saw something. Flights by police drones, as a part of the response, added to the confusion. Vigilant members of the public called in these police drones as suspicious.

In total there were 115 relevant sightings of which 93 were from “credible witnesses” such as a pilot, airport staff and police officers. By the time Gatwick resumed normal operations on 21 December, over 140,000 passengers suffered delayed flights. The cost to the airlines was around £50m.

And yet, despite CCTV coverage, reporters on scene and vigilance by the authorities, no tangible evidence exists of the drones. No photographs, no video clips. Even the military, with sophisticated tracking and jamming equipment, failed to provide substantiation.

At first, people feared a terrorist attack. Later the authorities speculated about environmentalists campaigning against a second runway. But, as no one came forward to claim responsibility, these theories faltered.

The Guardian newspaper has put together a lengthy piece on the whole event. Journalist Samira Shackle suggests the entire saga may be down to 'mass hysteria'.

Could helicopter activity on the opposite side of the airport have triggered the initial report? It's well-known that at night, humans have a reduced ability to judge distances. Also, we are incredibly inept when viewing fast-moving objects. There are many instances of mistaken sightings even by professional aviators.

Also, in this instance, it appears that recent terrorist attacks exacerbated the response. The 2017 Manchester Arena bombing and the London Bridge attack remained fresh in the mind of the authorities.

Did this mindset cause a reluctance to examine the absence of evidence? It's clear that Sussex Police, who handled the investigation, displayed an over-zealous attitude. Twelve armed officers storming the home of an innocent couple gives an insight.

The Gatwick drone incident raises the issue of confirmation bias driving a security response. Granted, the initial reaction of closing the runway was appropriate, given the reports received. Yet, what happened next suggests a lack of unbiased analysis. That, and an unwillingness to acknowledge mistakes, made matters worse. All this culminated in a severe impact on airport operations that costs millions.

The fundamental problem is this: the human brain evolved so that we sometimes misjudge risks and how to respond to them.

Reviewing all this, Occam's Razor came to mind. Other things being equal, more straightforward explanations are generally better than more complex ones. Did an honest mistake, caused by human limitations, escalate to have significant consequences? Looks like it.

Seen in retrospect, without the pressures of the moment, it’s easy to claim clarity. After all, I’m not sure how I’d have reacted given the available evidence at the time, except to ask why no photographs or video to verify the sightings.

Nonetheless, there are lessons to learn from the Gatwick incident. Even if our brains sometimes mislead us, they also provide us with the capacity to recognise our flaws and rectify mistakes. So we can adjust for our weaknesses in risk assessment.

The military deployed surveillance, scanning and jamming kit. They saw nothing.

What Really Happened At Gatwick?