Swiss aviation authorities launched an investigation on Wednesday after radar screens monitoring flights in the area of Switzerland’s busiest airport went blank for 20 minutes.
Swiss air traffic control company Skyguide said radar screens turned black at 7.37pm (6.37 GMT) on Tuesday at the Zurich Area Control Centre, which is responsible for planes approaching and leaving Zurich airport as well as flights passing through the surrounding airspace.
”The precise cause of the incident is still being investigated. The air traffic controllers on duty responded quickly, and immediately adopted emergency working procedures,” Skyguide said in a statement.
Controllers made radio contact with craft in their airspace and stopped further planes from entering the area. Control of planes coming in to land was switched to the control tower at Zurich airport, which was unaffected.
”Traffic levels were light at the time,” Skyguide said. It said the legal minimum distance between aircraft was maintained at all times.
Jean Overney, head of the Swiss Accident Investigation Bureau, said it was opening an investigation but the cause of the incident is not yet known. The screens started to come back after 10 minutes and were working correctly after 20 minutes, he said.
Skyguide has been under heavy scrutiny since a midair collision in July 2002 when a Bashkirian Airlines Tu-154 struck a Boeing 757 cargo plane flown by the package delivery service DHL International over in airspace controlled by the Swiss company.
Most of the 71 people who died when the planes came down in southern Germany were schoolchildren from the Russian city of Ufa on a trip to Spain.
Investigators have said the Russian crew received contradictory instructions from Skyguide, which ordered it to descend, and from its own collision-avoidance system, which instructed it to climb.
Germany’s federal air accident investigation office plans to release its report on the accident at the end of this year. — Sapa-AP