This paper argues that reliability assessments of complex technologies can usefully be con- strued as ‘audits’ and understood in relation to the literature on audit-practices. It looks at a specific calculative tool – redundancy – and explores its role in the assessments of new airframes by the Federal Aviation Administration (FAA). It explains the importance of redundancy to both design and assessment practices in aviation, but contests redundancy’s ability to accurately translate between them. It suggests that FAA reliability assessments serve a useful regulatory purpose by couching the qualitative work of engineers and regu- lators in an idiom of calculative objectivity, but cautions that this comes with potentially perverse consequences. For, like many audit-practices, reliability calculations are constitu- tive of their subjects, and their construal of redundancy shapes both airplanes and aviation praxis.