Notwithstanding subsection (a) of this section, an individual found to have used alcohol or a controlled substance after
October 28, 1991, in violation of law or a Government regulation may serve as an airman, crewmember, airport security screening employee, air carrier employee responsible for safety-sensitive functions (as decided by the Administrator), or employee of the Administration with responsibility for safety-sensitive functions only if the individual completes a rehabilitation program described in
section 45105 of this title.