In 1996, Ariane 5’s maiden flight failed because an inertial-reference software process converted a value outside its integer range without safely handling the overflow. The software had been reused from earlier rockets, whose flight conditions generated lower acceleration, and the process was not required for Ariane 5’s launch regime. A specification decision made the failure especially dangerous: instead of safely terminating or isolating the faulty calculation, the system issued a diagnostic data dump.
During flight, the diagnostic bus was connected to the rocket’s steering hardware rather than the test equipment used during development. The dump therefore drove the engine nozzle sharply to one side, placing the vehicle beyond aerodynamic control and causing its rapid breakup. The incident demonstrated that software previously considered reliable could fail when reused outside its original operating envelope, and that a benign testing interface could become a catastrophic control path when deployed in a live vehicle. The supplied source identifies the overflow and engineering specification as the primary causes, but does not report a separate legal or regulatory penalty.
