GENEVA, July 6: The Swiss air accident investigation bureau said on Friday that ground control recordings of the mid-air collision between two aircraft over southern Germany this week did not accurately reflect the data available to the ground controller on duty at the time.

In a statement issued on its Internet site, the Bureau indicated that the inherent flaw had been highlighted in a recent report recommending upgrades to the radar system used by Skyguide, the Swiss air traffic control agency.

Questions have been raised about the quality of information available to the Swiss air traffic controller on duty earlier this week when a Russian Tupolev airliner and Boeing cargo plane collided in mid-air, killing 71 people.

The aircraft were under the control of Skyguide. The Russian aircraft had been handed over to the Swiss by German ground control about five minutes before the crash.

The report by the Bureau last month highlighted discrepancies between the black box “legal recording” of radar displays at Skyguide and what controllers actually see on the screens.

It said ground control’s recording of Monday night’s accident, which is in the hands of the German-led air accident investigation, had shown a “short-term conflict alarm” being triggered.

However, it acknowledged that the controller was not given any automatic alert of a possible collision on the night because the system was in “fallback” mode while it was undergoing maintenance.

It did not say if the automatic alarm would have sounded before the controller managed to give a warning to the Russian plane, 44 seconds before the mid-air collision.

“The recording of the courses of the planes involved in the accident on the legal recording system do not correspond entirely to the display that was available to the controller,” the bureau added.

It also reiterated that the absence of a “primary radar source” at Skyguide was not, at the current stage of the inquiry, a factor in the accident, and that ground control had tracked both flights continuously using its standard secondary radar system.

But it gave more details on last month’s report, saying it had advocated the addition of a primary system because under certain circumstances aircraft “are not displayed on the controller’s screen or they disappear from the screen”.

It noted that “many other European countries” were in a similar situation.

Other problems with the precision of Swiss radar’s assessment of an aircraft’s position, which fell below Eurocontrol standards during a test in June 2000, had been improved by December 2000, the Bureau emphasised.

“For the moment, there is nothing to indicate that the precision of the representation of flights DHX 611 and BTC 2937 was insufficient,” the statement added.

The Bureau said its report last month was not meant to provide a comparison with other European systems.

“Such comparison work can only be carried out by an organisation such as Eurocontrol (the European air traffic agency)” the Bureau said in a statement issued on its Internet site.—AFP