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Neurological Disease at 30 000 Feet –What is an Acceptable Risk for your Pilot?
  1. R. V. Johnston*,
  2. M. D. O’Brien
  1. Clinical Tutor, Medical Division, Civil Aviation Authority, Gatwick RH6 0YR;
  2. Consultant Advisor in Neurology to the Civil Aviation Authority, Emeritus Physician for Nervous Diseases, Guy’s Hospital, London SE1 9RT; E-mail: ray.johnston{at}



Fitness to fly is not defined merely by the absence of disease. The standards for aircrew are such that even without significant disease an individual may not be considered fit to fly, for example if there is significant myopia. In contrast, even documented conditions, such as coronary artery disease, may not preclude fitness to fly in certain circumstances. The medical standards are set with the aim of maintaining flight safety at an acceptable level.


A zero risk environment is unattainable. In aviation therefore the concept of ‘acceptable risk’ has been developed (Tunstall-Pedoe 1984). This approach uses an overall fatal accident rate which is reasonably achievable (one in 10 million flights). To simplify the calculations which follow, each flight is deemed to last 1 hour, though most commercial flights are much longer. It is further postulated that no one component (crew failure, airworthiness, mechanical failure

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