1% rule (aviation medicine)

In aviation medicine, the 1% rule is a risk threshold that is applied to the medical fitness of pilots. The 1% rule states that a 1% per annum risk (See also risk management) of medical incapacitation is the threshold between acceptable and unacceptable. In other words:

Applying this 1 percent rule would result in an airline pilot being denied a medical certificate if their risk of a medical incapacitation (e.g. heart attack, convulsion, stroke, faint etc) was determined as being greater than 1% during the year.

This 1 percent rule began in the late 1980s and early 1990s in a series of British and then European aviation cardiology workshops. The application of this "1 percent rule" has subsequently spread beyond the domain of aviation cardiology to all potential causes of medical incapacitation.

The reasoning that was used in the development of the original aviation medical 1 percent rule is well described in Flight Safety and Medical Incapacitation Risk of Airline Pilots (see references). In this article the authors argue that changes in the underlying assumptions, that were the basis of the 1 percent rule, have been such that a 2 percent rule may be an appropriate modern analogue.

The application of this one percent rule is controversial. The civil aviation regulatory authorities of some nations employ such numerical risk thresholds while others do not. Of those that use numerical risk criteria there are differences in the levels of measured / calculated risk that are applied (1% per annum, 2% per annum etc.). There is also debate concerning the application of population statistics to an individual pilot and the utility and validity of the risk screening tools that are used by the civil aviation regulatory authorities (e.g. data from the Framingham Heart Study).

Application of the 1% Rule in Medical Assessments

• Aeromedical Decision-Making Framework: The 1% rule serves as a critical benchmark for aeromedical examiners (AMEs) when assessing pilots' fitness for duty. It establishes that if a pilot's risk of in-flight incapacitation exceeds 1% per year, they are deemed unfit for flying. This guideline helps standardize medical evaluations, ensuring that decisions are based on quantifiable risk rather than subjective judgment
• Integration with Other Risk Management Practices: The 1% rule is part of a broader risk management strategy in aviation safety. It complements other operational guidelines that limit the acceptable risk of pilot incapacitation to ensure that medical factors do not disproportionately contribute to flight safety risks. This holistic approach considers multiple variables, including pilot performance and environmental factors, when evaluating overall flight safety

Further reading

• Mitchell, Stuart J.; Evans, Anthony D. (March 2004). "Flight safety and medical incapacitation risk of airline pilots". Aviation, Space, and Environmental Medicine. 75 (3): 260–8. PMID 15018295.
• Tunstall-Pedoe, Hugh (March 1984). "Risk of a coronary heart attack in the normal population and how it might be modified in flyers". European Heart Journal. 5 (Suppl A): 43–9. doi:10.1093/eurheartj/5.suppl_A.43. PMID 6373281.
• Tunstall-Pedoe, Hugh (May 1988). "Acceptable cardiovascular risk in aircrew. Introduction". European Heart Journal. 9 (Suppl G): 9–11. doi:10.1093/eurheartj/9.suppl_G.9. PMID 3402499.
• Tunstall-Pedoe, Hugh (May 1988). "Acceptable cardiovascular risk in aircrew. The concept of risk". European Heart Journal. 9 (Suppl G): 13–5. doi:10.1093/eurheartj/9.suppl_G.13. PMID 3402489.
• Tunstall-Pedoe, Hugh (December 1992). "Cardiovascular risk and risk factors in the context of aircrew certification". European Heart Journal. 13 (Suppl H): 16–20. doi:10.1093/eurheartj/13.suppl_H.16. PMID 1493822.
• Niedermeier, W.; Küblbeck, K. (September 1991). "Faktorenerfassung zur Funktion enossaler Implantate" [Factors involved in endosseous implant function]. Deutsche Zahnärztliche Zeitschrift (in German). 46 (9): 589–94. PMID 1817937.
• Watson, Dougal B. (January 2005). "Aeromedical decision-making: an evidence-based risk management paradigm". Aviation, Space, and Environmental Medicine. 76 (1): 58–62. PMID 15672988.
• Mulloy, A.; Wielgosz, A. (August 2019). "Cardiovascular Risk Assessment in Pilots" Aerosp Med Hum Perform. 2019 Aug 1;90(8):730–734. [1]