Investigation under way after 13 planes mysteriously vanish from radars in Europe for 25 MINUTES in 'unprecedented' incident

The incidents on June 5 and 12 saw flight data disappear



A total of 13 planes suddenly vanished from radars on two occasions

Happened over Austria - neighbouring countries also reported blackouts



It is believed some of the planes were long-haul flights carrying passengers

Air traffic control was carried out 'blind' - by voice - during outage



A total of 13 aircraft suddenly vanished off radars for about 25 minutes on two occasions while flying over Austria, it has been revealed.

In what is being billed as 'unprecedented' circumstances, the incidents on June 5 and yesterday saw the flight data disappear from air controller screens.

Austria's flight safety organisation admitted that the height, location and other information for a total of 13 aircraft mysteriously vanished from radars.

'Unprecedented': The planes disappeared from radars over Austria. Pictured, air traffic controllers in Zurich

Investigation: Data for the planes disappeared as they were flying over Austria and other European countries

HOW IS A PLANE TRACKED?

Air traffic control monitors airspace using two radar systems: primary and secondary - which is the main system used worldwide for controlling aircraft.

The primary radar detects and measures the approximate position of aircraft using radio signals. The secondary radar, which relies on targets being equipped with a transponder, also requests additional information from the aircraft - such as its identity and altitude. All commercial aircraft are equipped with transponders, which automatically transmit a unique four-digit code when they receive a radio signal sent by radar. The code gives the plane's identity and radar stations go on to establish speed and direction. This flight data is then relayed to air traffic controllers. However, once an aircraft is more than 240km (150 miles) out to sea, radar coverage fades and high-frequency radio is used by air crew to keep in touch with those on the ground. GPS is only used by pilots to show their own position on a map, and these signals are not relayed to air traffic control. The 'Black Box' contains a cockpit voice recorder and a flight data recorder. They emit ultrasonic waves, but have limited range, and don't use GPS.



It is believed that some of the planes were long-haul flights carrying passengers on board.



Markus Pohanka, a spokesman for Austro Control, said relevant EU agencies have been asked to investigate the 'unprecedented' situation.

He added that other unnamed neighbouring countries had similar incidents and the EU's Eurocontrol, and European Aviation Safety Agency has been asked for a probe.

Pohanka did not identify the other nations that the European flights were flying over when they disappeared from secondary surveillance radars.

However, a report in the Kurier newspaper said as well as in Vienna in Austria, flight controllers in Munich and Karlsruhe in Germany, and in Prague, the Czech Republic, and Bratislava in Slovakia also reported related problems.

The report said German air traffic control had confirmed the black outs, adding that the reason there were no collisions was due to the air traffic controllers.

It could have had dramatic consequences, as 4,000 planes take to the sky in Austria every day - with 50 in the air at any one time, according to the report.

Air traffic was conducted 'blind' - by voice only - during the temporary outage, it claimed.

The revelations echo the circumstances surrounding missing Malaysia Airlines flight MH370 from Kuala Lumpur to Beijing which disappeared on March 8.



The Boeing 777 - with 239 passengers and crew on board - vanished from civilian radar screens about an hour into the night flight.



The search for the flight - which involves countries including the UK, the US, Australia, China, Japan, South Korea and New Zealand - has so far recovered nothing.



In relation to the 13 missing flights about Europe, Kurier cited unnamed experts as saying interference between the aircrafts' transponders and ground control was apparently to blame.

Map of locations over Europe which have reportedly experienced flight data black outs

Pohanka declined to confirm that or to say which airlines and planes were involved.

But he suggested that at least some may have been long-distance passenger aircraft, based on their high altitudes.



There was no danger at any time, he said.



Pohanka said extra air controllers immediately were called to their posts and emergency measures, including establishing voice contact with the pilots and widening flight corridors, were put into effect.



The EU’s Eurocontrol and European Aviation Safety Agency will investigate the incidents.

Missing: The news echoes the surroundings of the Malaysia Airlines flight that disappeared in March. Pictured, Malaysia Airlines aircraft parked on the tarmac at Kuala Lumpur International Airport

Pohanka said that safety in the Austrian air space was guaranteed at all times.

He told MailOnline Travel: 'There is no situation in aviation where there is not another procedure that takes place.

'We noticed that some of the responder data sent from the plane to the ground disappeared for a short period of time from the radar screens.

'That is the reason why the contingency procedures were put into place.

'Voice communication guaranteed that we knew everything about the planes in Austrian air space and allowed air traffic controllers to do their jobs.

'Distance between aircraft was increased.'