While preparing the Paris - Kiev flight AUI 3SD, the crew envisaged taking off from runway 26R and selected the corresponding SID on the FMC. When they received clearance for runway 27L, they did not modify the FMC data. After taking off, they followed the FD indications without realising that this path led to the aeroplane aligning with the axis of runway 26R. The risk of collision with the Paris – Bordeaux flight AF 48KZ, which was taking off from runway 26R was quickly detected by the air traffic controllers who used the emergency phraseology to separate the two traffic.
The longitudinal offset between the thresholds of runways 27L and 26R naturally ensures a vertical separation, in the climb-out, between two aeroplanes with similar performance taking off simultaneously. However, this separation is not guaranteed in all cases, in particular for an aeroplane with lower climb performance, taking off from runway 26R. During the loss of separation, the two aeroplanes were in IMC conditions and could not ensure a visual separation. A modification in the take-off temporality could have led to a much more serious loss of separation and the TCAS would have probably been the only barrier available to prevent a mid-air collision.
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