Air traffic controllers are meant to stop aircrafts from flying into one another... and if they fail, computer systems are installed to warn pilots of a coming collision. But sometimes these humans and computers give conflicting and confusing advice. Who to believe?

When a cargo plane and a Russian airliner collided in just such a situation, the authorities scrambled to work out how to prevent a repeat of the disaster... but a grieving father decided to seek revenge on those he held responsible. 

For a full list of sources for this episode, go to timharford.com.