Plot: What happens when the calculations of builders and engineers prove wrong and their constructs come tumbling down? In this episode, we examine the 1987 failure of the Schoharie Creek Bridge in New York; the partial destruction by a runaway freighter of the Riverwalk Marketplace in New Orleans in 1996; the roof collapse of the Rosemont Horizon Arena in Illinois in 1979; the deadliest grain-dust explosion on record in Westwego, Louisiana, when a grain elevator exploded in 1977; and the crash of the British R101 airship in the 1920s.