From:
FAR Part 91 Sec. 91.17 effective as of 07/21/2006
Alcohol or drugs.
(a) No person may act or attempt to act as a crewmember of a civil aircraft--
(1) Within 8 hours after the consumption of any alcoholic beverage;
(2) While under the influence of alcohol;
(3) While using any drug that affects the person's faculties in any way contrary to safety; or
[(4) While having an alcohol concentration of 0.04 or greater in a blood or breath specimen. Alcohol concentration means grams of alcohol per deciliter of blood or grams of alcohol per 210 liters of breath.]