It seems from the reports that the Russian pilot didn't respond to ATC, and the DHL pilot descended in response to TCAS.
Was the Russian on the wrong frequency? Or was his avoidance system faulty? Or neither?
Who knows. The worst irony, as the bbc quoted, was that the children on the Russian flight had the flight specially chartered so that they would not miss any of their holiday. The parents believed their children were already enjoying themselves.
Let's hope they recover the black boxes in order to find out the true reason for this tragedy, to help avert another one.
