The A319, registered LZ-FBB and operated by Bulgaria Air, call sign LZB431, was carrying out a flight from Sofia to Paris.
The A320, registered TC-FBJ and operated by Freebird Airlines, call sign FHY542, was carrying out a flight from Paris to Istanbul.
At 08:18:43, the controller told the crew of flight LZB431 to hold short of runway 08L at holding point S6. The crew of flight LZB431 correctly read back. At 08:18:51, the controller cleared the crew of flight FHY542 to take off from runway 08L. Another aeroplane, AFR1089, landed on runway 08R and vacated via taxiway V6. At 08:19:34, the controller told the crew of flight LZB431 that they were number one and to keep on taxiing. The crew of flight LZB431 read back using the same terms as the controller. At 08:19:37, the controller told the crew of flight AFR1089 to taxi behind the 319 Bulgaria on left. The crew of flight AFR1089 asked whether they were cleared to cross. The controller replied no. At 08:20:17, LZB431 entered runway 08L via S6. The RIMCAS warning was triggered one second later. FHY542, performing the take-off run, was at approximately 1,500 m before the intersection with taxiway S6 and at an indicated airspeed of 139 kt. At 08:20:37, FHY542 flew over the intersection with S6 at a height of around 500 ft. LZB431 had vacated the runway and was stopped on taxiway T9.
The event took place during a period of dense inbound traffic with aircraft arriving with a reduced separation. This additional workload led the controller to pay greater attention to inbound aeroplanes, probably to the detriment of those on the ground, in particular when they were no longer on the runway. Inadequate phraseology was used to deal with the taxiing priorities between Air France flight 1089 and Bulgaria Air flight 431. The message, “Bulgaria 4 3 1, number one, keep on taxiing” was not accompanied by a reminder that they must hold short of runway 08L. This led to the crew of the Bulgaria Air flight erroneously interpreting the message and understanding it as a clearance to cross the runway.