1996 Charkhi Dadri Mid-air collision

Saudi Arabian Airlines Flight 763
Saudi Arabian Airlines Flight 763 was a passenger flight from Delhi to Dhahran, Saudi Arabia carrying 312 people. The flight had no issues until the collision.

Kazakhstan Airlines Flight 1907
Kazakhstan Airlines Flight 1907 was a passenger flight from Shymkent, Kazakhstan to Delhi carrying 37 people. It was this planes fault for the accident.

The Collision
Saudi Arabian Flight 763 has taken off from Indria Gandhi International Airport, and is now climbing to 14,000 ft. They were told to stay at that altitude as nearby Kazakhstan Airlines Flight 1907 is at 15,000. ATC warns both pilots of the incoming traffic, and both flights register the warning. But then, the two planes collide. A nearby US Military aircraft sees a large explosion from his window, and realises the two aircraft have hit each other. He communicates it to ATC, who sees both planes off of his radar. He too realises that something catastrophic has happened. 349 people have died in one moment, making this the worst mid-air collision ever. Now the question is, why?

Investigation
The next morning, investigation teams have made it to the crash site. Hope of finding any survivors is immediately lost. People noted finding burnt corpses handing from trees, and that every time you stepped, what you stepped on was either plane wreckage or a dead body. The investigation eventually came to the conclusion that the Kazakhstan Airlines Flight 1907 descended beneath Flight 763 as the First Officer thought the message to descend to 14,000 ft was for them, and not for the nearby Saudi flight. The radio officer was the only person in the crew that understood the message, as he was fluent in English, rather the other crew were not. The radio officer noticed that the flight was at 14,000 ft and told them to climb back up to 15,000 ft, but that was the move that killed them. The flight had moved beneath Flight 763, so when they climbed back up they collided directly into the other plane.

This air incident is the 5th worst in history, and those who died will always be remembered.