A vital piece of safety equipment in the Swiss traffic control centre at Zurich was switched off during Monday鈥檚 mid-air crash over Germany, which killed 71 people.
This may have contributed to the lateness of the air traffic controller鈥檚 warning to the pilots, a factor that is one of a number of uncanny parallels emerging between Monday鈥檚 crash and a near miss in 1999.
In both cases the Zurich traffic control centre was in charge and in both cases pilots received emergency instruction to change course from the ground and from on-board collision avoidance systems.
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In 1999, the initial cause of the near miss was 鈥渁 brief lack of attention on the part of the radar controller鈥�, according to the official report from the Swiss Aircraft Accident Investigation Bureau.
Conflict alert
The safety equipment that was turned off on Monday at the Zurich air traffic control centre was a 鈥渟hort term conflict alert鈥�. This warns the controller that two planes are on a collision course.
It was switched off 鈥渇or routine maintenance鈥�, according to a spokesman for Skyguide, the Swiss air traffic control.
When the Russian plane entered Swiss airspace on its way to Barcelona it was flying at 36,000 feet. It was only told to reduce its altitude to 35,000 feet four minutes later 鈥� less than 60 seconds before the fatal crash.
Dangerous encounter
The near miss happened in September 1999 when a French plane flying from Munich to Lyons and a Crossair plane flying from Geneva to Dusseldorf came within just one second of a mid-air crash.
The official report calls this 鈥渁 dangerous encounter鈥� and says that the 鈥渟hort term collision alert at air traffic control signalled very late鈥�. In this case, catastrophe was avoided because the Geneva-bound plane had already been warned of the danger by its on-board collision detector and had started to climb.
A statement from Skyguide about Monday鈥檚 accident confirms that the Russian airplane did begin to dive when the controller repeated his radio request. 鈥淎t the same time,鈥� says the statement, the collision warning system on the Boeing 757 also told the pilot to dive, with tragic consequences.
The statement continues: 鈥淔ollowing these actions the symbols for both aircraft remained visible on the radar screen for around half a minute.鈥�