Prince Williamn with an East Anglian Air Ambulance (EAAA) in the background. Photo / AP
Prince William was at the centre of a major security alert last night after The Mail on Sunday discovered that terrorists could use a mobile phone to track his every movement in his new job as an air ambulance pilot.
Experts warned of the 'extraordinary risk' to the future King presented by a £2.99 app, which gives away precise details of his helicopter's position, direction of travel, speed and altitude.
Former police officers said the information presented 'intelligence gold' for terrorists wishing to track the Prince's flightpath in an attempt to shoot him down.
Astonishingly, subscribers can even opt to receive alerts every time the Prince's East Anglian Air Ambulance takes off from its base at Cambridge Airport on a 999 rescue mission, relaying real-time flight data from the helicopter's on-board transponder.
The app also reveals where the air ambulance lands.
Although Prince William's presence on official visits is often publicised in advance, security experts stressed that when he arrives at the scene of an emergency the area will not have been screened in advance.
A Mail on Sunday team last week used the app, called flightradar24, to monitor Prince William's progress as he flew from North Norfolk after attending a road accident.
Using the detailed information on the screen, we were able to have a photographer waiting at the precise moment the helicopter came into land at the airport.
A terrorist armed with a rocket-propelled grenade, ground-to-air missile or even less sophisticated weaponry would have had little difficulty targeting William's aircraft as it regularly flies below 1,500ft with a cruising speed of just 150mph.
Roy Ramm, a former Commander of Specialist Operations at Scotland Yard and an ex-head of the Flying Squad, called for immediate action to shut down the security loophole.
He said: 'Knowing the precise movements, altitude and speed of an aircraft in flight is intelligence gold for any terrorist. The ability to track a high-profile target like this presents a really serious risk.
'Even without expensive and sophisticated weaponry, there is the real danger that an inexpensive drone could be used to put any aircraft flown by William at risk.
'There is also the risk that a terrorist might simply open fire on his aircraft at low altitude with the kind of automatic weapon readily available to gangs in London. After all, the Prince is flying an air ambulance, not an armoured gunship.'
Only last week the Civil Aviation Authority warned of the risks that readily available drones could cause if they collided with aircraft.
Buckingham Palace and the Metropolitan Police, who are tasked with Royal protection, declined to comment when The Mail on Sunday alerted them to the app.
But it appeared last night that urgent efforts were being made to remove information relating to the Prince's air ambulance from flightradar24.
While most commercial and civilian aircraft can be tracked by the app, military and diplomatic flights and private jets do not normally appear for security reasons.
But until yesterday evening, detailed information of the Prince's missions in his air ambulance helicopter, codenamed 'Anglia Two', was available every time he took to the skies. The data is also available on the flightradar24 website for free as well as via the app.
Princess Diana's former personal protection officer Ken Wharfe added: 'It's madness to have his flight details displayed in this way on an open website, and it should have been addressed long before now.
'Prince William is a target whether he likes it or not, and it just takes one nutter with a gun to act on this information and take a potshot.
'More generally, I would question the security risks of Prince William doing this job at all. It would be far preferable, if he's determined to fly helicopters, to do so in the secure environment of an RAF base, where he could be an instructor, rather than attending road accidents on the streets of King's Lynn.'
Former head of the Met's Royalty Protection Squad, retired chief superintendent Dai Davies, said: 'This would give me cause for concern and solutions need to be found by those in charge of the Prince's security.
'You always have to be aware of the advance of technology - which this illustrates - and the ability of these terrorist groups to think outside the box. You always, always have to be one step ahead.'
Former Conservative Cabinet Minister Andrew Mitchell said: 'I congratulate The Mail on Sunday for exposing this significant flaw in Prince William's security. I urge the authorities to take urgent and firm action to correct it.'
Unlike William's civilian helicopter, most military aircraft do not show up on the tracking website, and normally neither does the US President's airliner, Air Force One.
Just last year, the Japanese government made a successful request to flightradar24 have their own VIP aircraft details removed from the site.
Several flight tracking websites and mobile phone apps provide live tracking of hundreds of aircraft flying over Britain, including the Prince's helicopter. But the flightradar24 app is the market leader and offers the most sophisticated service, using information from more than 7,000 worldwide receivers which pick up aircraft transponder signals. The basic version of the app is available to any smartphone user and costs just £2.99.
Users can enter the registration number of the East Anglian Air Ambulance's Anglia Two helicopter which Prince William started flying earlier this month. If the Eurocopter is in the air, it can be seen flying across a map on the screen which can be enlarged to show greater detail.
Anyone can pay an extra £3.99 for a 'custom alert', creating a message on their phones every time the helicopter takes off.
The alert flashes up on screen and makes an audible sound like a text message. Users can then search for the helicopter to track it on a map. Another button can be clicked to reveal the helicopter's speed, direction of flight, and its precise latitude and longitude position as it changes.
The air ambulance's flight path is easy to predict as it generally flies in a straight line while heading to an emergency, taking patients to hospitals or returning to base.
A Mail on Sunday reporter took just seconds to find the registration number of the Prince's helicopter after searching on aviation websites. The reporter then bought the flightradar24 app and paid the extra £3.99 to get an alert every time it is tracked.
He got an alert when the Prince and his crewmates took off after attending a road crash in Dersingham, Norfolk, last Tuesday. The reporter watched on his phone as the app provided live tracking of William's 50-mile flight back to Cambridge Airport.
A photographer was able to predict the Prince's arrival time and got into position by the airport fence just seconds before his helicopter appeared.
He was able to photograph it as it came in to land - but a terrorist using the same app might have been armed with more than a camera. The photographer took pictures of William after he left his helicopter a few minutes later and stood around chatting to his colleagues.
The Prince was on leave on Wednesday when he and wife Kate held a second birthday party for Prince George at their family home, Anmer Hall on the Sandringham estate.
He was not working again on Thursday when the MoS tracked Anglia Two on a 999 call to help a man who had been found unconscious in Culford, near Bury St Edmunds, Suffolk.
The helicopter flew to the scene at 100mph and landed in a field where it stayed for around 30 minutes, giving a MoS photographer time to get in position about quarter of a mile away.
He photographed the helicopter as it flew overhead at low altitude on its way back to Cambridge Airport after efforts to save the man failed and he was pronounced dead at the scene.
The MoS also tracked a second rescue mission carried out by a late-shift crew who helped a man found bleeding in St Albans, Hertfordshire, later on Thursday afternoon.
Once again a photographer was able to get in position and snap the helicopter on its return, although it is understood that Prince William was not on duty at the time.
Flightradar24's data mainly comes from 'automatic dependent surveillance-broadcast' (ADS-B) transponders , which are fitted to 70 per cent of commercial passenger aircraft. The transponders record an aircraft's position using GPS satellites in a similar way to sat nav systems, then broadcast the information to ground stations monitored by flightradar24.
The ADS-B transponders are not generally fitted to military aircraft and many older commercial aircraft.
A spokesman for the Bond Aviation Group, which operates the two East Anglian Air Ambulance helicopters, refused to say if the company was able to take any action to make Anglia Two invisible on tracking websites.
He added that the company was aware of the flightradar24 app. But he added: 'Bond cannot comment on the security arrangements'
Flightradar24 did not respond to requests for comment.
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