Disaster was averted when an undergraduate telephoned the designer of a Manhattan skyscraper to highlight a construction flaw: The joints in the chevrons were bolts, not welds. The 59-storey Citigroup Center was erected on top of four stilts in 1977 to avoid an historic church below, but Diane Hartley's call to engineer William LeMessurier to query whether a hurricane could collapse the building resulted in an emergency redesign to tackle the flaw she highlighted.