The crash of the Russian TU-154 airliner over the Black Sea on October 4 resulted from "a tragic coincidence of causes of technological nature," according to a tentative conclusion reached by Russian and Ukrainian experts after a test on the Cape Opuk testing ground, Secretary of the Russian Security Council Vladimir Rushailo cited in remarks to the press. Rushailo said the test "regenerated in real time scale the aerial situation over the area of the Black Sea at the moment of the Ukrainian Air Defense forces' exercise linked to the S-200 missile launch on October 4." Russian and Ukrainian experts serving on government commissions of either country studied "the order and rules of mutual exchange of information on the aerial situation during the exercise period and other data of objective control instruments," the Secretary said. He announced that the probe focused on the documents governing coordination between Russian Black Sea Fleet elements and Ukrainian air defense forces during joint use of facilities of the 31st testing center of the Russian Defense Ministry and the amphibious landing ground. "The issue looked into the most closely is the possibility of the missile homing head locking on the crashed TU-154 plane after a target tracking failure," he said. He referred the reporters to the Ukrainian side for definitive conclusions and pointed out that the Russian government commission had provided the Ukrainians with all the documents necessary.