BEA Trident at Split 1976
This was a mid air collision over Zagreb between a BA Trident in cruise and an Inex-Adria DC9 climbing out of Split. Cause was ATC failure to co-ordinate the DC9's climb so as to maintain separation between both aircraft. As ever it took several steps for holes in cheese to line up including communication errors between mid and upper sector controllers, staff not all at their post, premature withdrawal of a 'squawk' code and a late check in on upper sector by the DC9
The language used initially was English and with a potential opportunity for Trident crew to pick up an SA prompt when the Adria flight checked as climbing towards their level and with same estimate over Zagreb VOR.
The controller only lapsed into Serbo-Croat, either by instinct or for emphasis, when finally realising potential disaster was imminent within seconds.
The accident report is
here: