One cast destroyed Ariane 5
Did you know one integer conversion destroyed a rocket in 40 seconds?
· 28-sec read
On June 4, 1996, Ariane 5's first flight broke up about 40 seconds after the flight sequence began. Inertial reference software reused from Ariane 4 converted a 64-bit floating-point value to a 16-bit signed integer; Ariane 5's faster trajectory overflowed it. Both the primary and backup units failed the same way, and the flight computer read the diagnostic output as flight data. The inquiry found that, after liftoff, the alignment function that failed "serves no purpose."
Why it matters
Redundancy doesn't help when both copies run the same code. Re-validate reused components for their new operating range.
Sources
High confidenceChecked October 20, 2026.
- Ariane 5 Flight 501 Failure: Report by the Inquiry Board (ESA, 1996) csapp.cs.cmu.edu