Ariane 5 Flight 101
Ariane 5 Flight 101 shows that software proven reliable in one system may become unsafe when reused under different operating conditions. The rocket, Ariane 5, was destroyed shortly after its first launch in June 1996 after its inertial-reference software attempted to place a value into a format too small to contain it. The resulting error caused both the primary and backup guidance units, which used essentially the same software, to fail. The software had been inherited from Ariane 4, but assumptions that were valid for the earlier rocket did not fit Ariane 5’s flight behavior. The main ethical question is whether engineers may treat previously successful software as adequately tested without reconsidering its assumptions in a new system. This case highlights common-mode failure, software reuse, inadequate system-level testing, and the false security created by two identical backup systems.