In what amounts to a harsh indictment of the French process for executing complex public projects, investigators have identified two likely reasons for the partial roof collapse at the 650-meter-long concourse at Paris Charles de Gaulle airport last May 23. Systemic flaws in designing the technically difficult building contributed to deficiencies that led to the early morning failure that caused four deaths.

The government-appointed team identified two key failure mechanisms but cannot say which was the primary trigger. The design process was insufficiently rigorous for so complex a structure, investigators said at a press conference on Feb. 15. No detailed, independent analysis was done to check design models.