INTRODUCTION: An aviation safety management system should consider and mitigate against all potential risks to flight safety. In addition to in-flight incapacitation, pilots falling below regulatory standards who are assessed as unfit may have represented a risk prior to that assessment. An analysis was undertaken of Class 1 certificate holders to determine factors correlated with unfit assessments.METHODS: Fitness assessments of pre-existing Class 1 certificate holders following medical examinations (to EASA Part-MED standards) or between medicals were studied between 1 January 2016 and 31 December 2019. Assessments where the outcome was ‘fit’ (N= 99,406) were compared with those where the outcome was ‘unfit’ (N= 7925). Analyses for correlation between unfit assessments against age, declared coexisting medical conditions, and the number of days since last assessed as fit were undertaken using SPSS.RESULTS: Unfit assessment likelihood and age were strongly correlated; there is, however, evidence for the ‘healthy worker effect’, with a fall in unfit assessments between 60–65 yr of age. There was no association between coexisting medical condition declaration and the likelihood of becoming unfit. The time interval between a fit and unfit assessment was significantly lower when comparing 20–60 and 61–63 yr old individuals.DISCUSSION: The analysis of unfit assessments shows strong correlation with increasing age and the possible presence of the healthy worker effect among commercial pilots. The decreased time from a previous fit assessment to an unfit assessment supports the reduced certificate validity period of Class 1 applicants over 60 yr of age.Cairns MK. Unfit assessments of Class 1 Medical certificate holders. Aerosp Med Hum Perform. 2021; 92(12):945–949