What is the maximum blood alcohol concentration permitted for someone acting as a crew member of a civil aircraft?

The maximum blood alcohol concentration (BAC) permitted for a crew member of a civil aircraft is 0.04 percent by weight. This standard is established to ensure the safety and performance of flight crew personnel, as alcohol can significantly impair cognitive and motor functions, which are critical for operating an aircraft safely.

At this BAC threshold, the regulations aim to provide a clear and enforceable limit that is lower than what is often considered the legal driving limit in many jurisdictions. By maintaining this standard, aviation authorities strive to minimize the risks associated with impaired performance while flying, ensuring that crew members can make sound judgments and react effectively to any in-flight emergencies.

Using the other options for comparison, a BAC of 0.08 percent typically corresponds with legal limits set for driving under the influence in many places but is deemed too high for crew members operating aircraft. A BAC of 0.008 percent and 0.004 percent would indicate extremely low levels of alcohol consumption, but those levels are not the operational standard established for crew members, which is why 0.04 percent is the correct choice.