What two airlines involved worlds worst air disaster?
The air Tenerife disaster, KLM Flight 4805 and Pan AM Flight 1736. The two planes had crashed in to one another.
Since you have used the word "disaster" meaning widespread destruction and distress, I would have to say the terrorist attacks on 9/11 to the World Trade Center would be considered the worst aviation disaster that led to about 2,800 deaths. The worst aviation accident, would be the Tenerife disaster was the worst to 747's ran into each other 03/27/77 there were 583 fatalities.