14 CFR Part 382 Nondiscrimination on the Basis of Disability in Air Travel (Air Carrier Access Act) (with amendments issued through May 2016)
(1) You can determine that there is a disability-related safety basis for refusing to provide transportation to a passenger with a disability if you are able to demonstrate that the passenger poses a direct threat (see definition in §382.3). In determining whether an individual poses a direct threat, you must make an individualized assessment, based on reasonable judgment that relies on current medical knowledge or on the best available objective evidence, to ascertain:
(i) The nature, duration, and severity of the risk;
(ii) The probability that the potential harm to the health and safety of others will actually occur; and
(iii) Whether reasonable modifications of policies, practices, or procedures will mitigate the risk.