* Dozens of aircraft affected in incidents on June 5 and 10
* Investigation under way into possible cause
* Slovak authorities blame "military exercise" for outages
(Adds comments from Slovakia)
VIENNA/PRAGUE, June 13 Dozens of aircraft
briefly vanished from air-traffic control radars in Austria,
Germany, the Czech Republic and Slovakia this week and last in
separate incidents that Slovak authorities blamed on military
electronic warfare exercises.
Air-traffic controllers in Austria and Germany said data
about the planes' position, direction, height or speed went
missing on June 5 and June 10, but the outages posed no serious
danger to people on the aircraft travelling at high altitude.
Their Czech and Slovak counterparts also encountered cases
of vanishing aircraft on the same days.
"The disappearance of objects on radar screens was connected
with a planned military exercise which took place in various
parts of Europe on June 5 and 10 and whose goal was the
interruption of radiocommunication frequencies," the Slovak
state Air Traffic Services company said in a statement.
"This activity also caused the temporary disappearance of
several targets on the radar display, while in the meantime the
planes were in radio contact with air traffic controllers and
continued in their flight normally.
"Immediately after the identification of the problem with
the displays, the side organising the exercises was contacted
and the exercise was stopped."
It did not identify the military force, which Austrian media
said was the NATO western military alliance. NATO had no
A spokesman for German Air Traffic Control said: "Planes
disappeared from screens for a matter of seconds, here and
there. The outages were sporadic and not grave."
"It must have been an external source of disruption. We are
trying to identify the cause," the spokesman said.
In the wake of the disappearance of Malaysian Airlines
flight MH370 in March there has been a growing focus on the
tracking of passenger aircraft.
The airline industry has pledged to come up with proposals
by September for a better system of tracking aircraft over
oceans and other remote areas. But incidents in controlled
airspace are relatively rare.
Europe's air corridors are among the densest in the world
and there have been calls for better technology and coordination
and a unified control network, although some air traffic
controller unions oppose these measures.
In the recent incidents, extra air-traffic controllers
stepped in in Austria and communicated with the affected planes
by radio and took steps including increasing the safety
distances between planes, a spokesman for Austro Control said.
He said that 10 planes transiting Austrian airspace were
affected in the first incident and three in the second, and that
he had heard that 50 aircraft were affected across Europe.
The incidents are being dealt with by European air
navigation safety organisation Eurocontrol and EASA, the
European air safety agency, he said. Neither of these bodies
could immediately be reached for comment.
Richard Klima, spokesman for the Czech Air Navigation
Service, said: "We saw random outages of aircraft detection
within the system of the so-called secondary radar lasting
several tens of seconds and up to several minutes. But thanks to
the complete coverage of air space also through classic primary
radars, we constantly had information about the positioning of
airplanes and operational safety was not threatened."
A spokesman for Austria's Defence Ministry said it was
investigating the incidents but could not immediately confirm
how many planes were involved.
The spokesman said military radar - which actively track
plane movements, unlike the passive radar used by civilian
air-traffic control - had continued to work at all times.
(Reporting by Georgina Prodhan and Michael Shields in Vienna,
Tim Hepher in Paris, Ludwig Burger in Frankfurt, Adrian Croft in
Brussels and Jason Hovet in the Czech Republic; Editing by