Prince William’s air ambulance has come within half a second of a catastrophic mid-air collision with a remote-controlled drone

Prince William’s air ambulance has come within half a second of a catastrophic mid-air collision with a remote-controlled drone.

Medics on board reacted with horror when they spotted the device within feet of potentially downing their helicopter.

An official report, seen by The Mail on Sunday, said that ‘a collision had only been narrowly avoided’ and disaster was averted by pure ‘chance’.

Last night aviation experts said the drone could have downed the helicopter, killing those on board and potentially causing more casualties on the ground.

The report reveals that the terrifying near-miss happened at 1,900ft when the helicopter, with three medical staff and two pilots on board, was flying almost directly over a McDonald’s restaurant filled with families.

It was flying at 138mph, covering 200ft a second, and the drone was less than 100ft away – making it half a second from impact.

The Duke of Cambridge regularly pilots the helicopter, codenamed Anglia Two, but it was only by fluke that he was not on board at the time. He was at the controls of the aircraft just days later.

Police on the ground were alerted, but failed to capture the operator of the drone, which was flying well above the legal height.

It is not known if the near-miss was a reckless mistake or a deliberate act.

A Mail on Sunday investigation previously revealed how terrorists could use a £2.99 mobile phone app to monitor the exact movement of William’s East Anglia Air Ambulance in real time.

The Anglia Two lands so that a medic could attend to a boy, who had been injured in a road accident. The helicopter then drops the patient at the Royal London Hospital. Nine miles back to its Cambridge base, the helicopter comes dangerously close to a drone

The aircraft was removed from the app after our revelations.

The Eurocopter 145 narrowly missed the drone when it was flying over Brimsdown on the outskirts of Enfield, North London, while returning to its base at Cambridge airport.

The device is thought to be about eight inches across – too small to be picked up by air traffic control radar but large enough to cause serious damage in a collision.

A report by the UK Airprox Board, which investigates near-collisions in UK airspace, rated it as a Category A incident due to there being a ‘serious risk of collision’.

The report said that the drone was flown ‘into conflict’ with the helicopter over a built-up area without Civil Aviation Authority permission at 7.45pm on August 26 last year, effectively ‘endangering the EC145 and its crew’.

Hours after the near-miss, Casualty imagined the horror of a drone hitting an air ambulance. The helicopter smashes into an ambulance after being drowned by a drone hitting its tall rotar, then ends up crashed on its side in the hospital car park, causing multiple injuries

The drone, a four-bladed quadcopter with two red lights, was spotted by medical personnel in the back of the helicopter.

The shocked medics yelled at the male pilot after seeing the drone appearing to be ‘in a turn away from the aircraft’ on the right hand side just 98ft away.

The pilot, who rated the chance of a collision as ‘high’, immediately informed air traffic controllers and ambulance control staff, telling them to alert police on the ground.

The report said: ‘The board considered that the reported range was such that this was a situation where a collision had only been narrowly avoided and chance had played a major part.’

The Duke of Cambridge regularly pilots the helicopter, codenamed Anglia Two, but it was only by fluke that he was not on board at the time. He was at the controls of the aircraft just days later

The helicopter had earlier been flown to help an 11-year-old boy who had suffered serious leg injuries after being hit by a double decker bus in Wickford, near Basildon, Essex. The crew flew the boy to the Royal London Hospital in Whitechapel.

They were heading back to Cambridge when they experienced the near-miss, around nine miles into the 40-mile flight.

Aviation consultant Paul Beaver, a former Army helicopter pilot, said: ‘A collision between even a small drone used for taking photographs and a helicopter could be catastrophic.

‘A drone would be big enough and heavy enough to penetrate the Plexiglas screen of the cockpit, which is only designed to withstand rain, sleet and hail or a collision with a small bird.

‘It would be catastrophic if it hit the tail rotor system and a potential serious danger if it hit the main rotor. This highlights the problem with drones.

They can be bought cheaply and are simple enough to fly, but they have a capability which ten years ago would only have been in the hands of the military.’

Dai Whittingham, chief executive of the UK Flight Safety Committee, said: ‘A collision between a helicopter and a drone could have very serious consequences.

‘It would be made potentially worse by the fact that drones have lithium batteries which can explode on impact.

‘Helicopters are at more risk than fixed wing aircraft, partly because their windscreen canopies are larger and not as strong, due to weight having to be kept down.

A drone would be quite likely to go through the screen at the speed this helicopter was flying, depending on the angle of impact and where it hit. It could be fatal for the pilots.

‘The rotating parts of a helicopter, especially the tail rotor, are also very vulnerable. A drone strike in the tail rotor could cause a catastrophic loss of control.

‘A helicopter could easily become uncontrollable and start to tumble with the cab rotating around the rotor.

You wouldn’t know where it was going to go. A drone could also sever hydraulic lines or interfere with the gearbox.’

William is thought to have been concerned for many years about drones being used by paparazzi photographers to take pictures or potentially by terrorists to deliver bombs or chemical weapons

Drones cost as little as £25 and can travel at up to 50mph, but do not require a licence to operate. Tens of thousands of the devices have been sold in Britain since they have become affordable for consumers.

The near-miss happened just a day before BBC1 screened an episode of Casualty that featured a dramatic storyline about an air ambulance crashing after hitting a drone flown by a small boy.

Millions of viewers saw the helicopter spin out of control and smash into fictional Holby City Hospital, sending debris flying and causing multiple casualties in a special episode to mark the show’s 30th anniversary.

The increasing popularity of drones has led to growing numbers of near-misses. The UK Airprox Board conducted just six investigations into incidents involving drones in 2014, compared to 56 in the first ten months of last year.

The Duke of Cambridge is believed to have been instrumental in getting the Government to introduce special rules in December 2015, banning any aircraft, including drones, from being flown within a mile and a half of Anmer Hall

Last month it was revealed that a twin-rotor RAF Chinook flying at nearly 140mph came within 130ft of crashing into a drone at 2,100ft while it was coming into land at RAF Odiham, Hampshire, on August 15 last year.

A UK Airprox Board report stated that the Chinook pilot believed the drone could have caused ‘the loss of the helicopter’ if it hit a vulnerable spot.

A suspected drone was reported to have collided with British Airways jet carrying 120 passengers and five crew at 1,700ft as it was preparing to land at Heathrow after flying from Geneva last April.

But Transport Minister Robert Goodwill later said that the Airbus 320 might only have collided with a plastic bag.

The Government started a consultation in December over possible new rules for drones following mounting concern about their misuse.

The crackdown will potentially include the mandatory registration of new drones, tougher penalties for illegal flying, new signs at no-fly zones such as airports and prisons and making drones electronically identifiable so owner’s details can be passed to police if they are seen breaking the law.

Drones are usually limited to flying beneath 400ft. They can fly higher if they weigh less than 3.5kg and have an on-board camera with a live feed and an observer overseeing the operator.

The near-miss happened just a day before BBC1 screened an episode of Casualty that featured a story about an air ambulance that crashed into a drone. Drones are restricted to flying at 1,000ft

Even then, the flying height is restricted to 1,000ft so the drone which nearly hit the air ambulance would still have been nearly twice its permitted limit.

Anyone breaking the rules faces a maximum penalty of five years imprisonment for endangering an aircraft.

William has been working around 20 hours a week as a pilot in the last 20 months, flying scores of missions and helping save numerous lives.

He has announced that he will be quitting in the summer and moving his family’s main home from Anmer Hall, Norfolk, to Kensington Palace to spend more time on Royal duties – but until then he will continue to fly the air ambulance.

Millions of viewers saw the helicopter spin out of control and smash into fictional Holby City Hospital. The Government started a consultation in December over possible new rules for drones following mounting concern about their misuse

William is thought to have been concerned for many years about drones being used by paparazzi photographers to take pictures or potentially by terrorists to deliver bombs or chemical weapons.

He is believed to have been instrumental in getting the Government to introduce special rules in December 2015, banning any aircraft, including drones, from being flown within a mile and a half of Anmer Hall.

A spokeswoman for the East Anglian Air Ambulance said: ‘We can confirm that, in accordance with aviation regulations and procedures, a pilot reported a drone in his proximity on August 26, 2016.

‘The Duke of Cambridge was not on shift when the drone incident took place. There are strict rules that drone operators must follow and it is important they are aware of their responsibilities for safe operations at all times.’

Kensington Palace refused to comment.