The launch ended in failure due to multiple errors in the software design: dead code, intended only for Ariane 4, with inadequate protection against integer overflow led to an exception handled inappropriately, halting the whole otherwise unaffected inertial navigation system.

The active module presented a diagnostic bit pattern to the On-Board Computer which was interpreted as flight data, in particular causing full nozzle deflections of the solid boosters and the Vulcain main engine.

This led to an angle of attack of more than 20 degrees, causing separation of the boosters from the main stage, the triggering of the self-destruct system of the launcher, and the destruction of the flight.

[4] The official report on the crash (conducted by an inquiry board headed by Jacques-Louis Lions) noted that "An underlying theme in the development of Ariane 5 is the bias towards the mitigation of random failure.

The supplier of the inertial navigation system (SRI) was only following the specification given to it, which stipulated that in the event of any detected exception the processor was to be stopped.

There is reason for concern that a software exception should be allowed, or even required, to cause a processor to halt while handling mission-critical equipment.