Personal Observations on Reliability of Shuttle is Richard Feynman’s appendix to the report of the Presidential Commission investigating the Space Shuttle Challenger accident. Feynman examines substantial differences between NASA management and working engineers over estimates of Shuttle reliability. He considers the solid rocket boosters, main engines and avionics, questioning how previous successful flights and changing certification standards were sometimes used to justify continued operation despite unresolved technical problems.

Feynman argues that reliable engineering depends on understanding failures, testing assumptions and acknowledging uncertainty rather than adjusting safety criteria to meet operational schedules. He contrasts weaknesses in the treatment of mechanical problems with the more rigorous testing practices used for Shuttle computer software. The appendix also examines communication between engineers and management and the risks of presenting technical systems as safer than the evidence supports. Feynman concludes that decisions about complex technology must remain grounded in physical evidence and realistic assessments of risk.