Definition
The concentration of alcohol present in a person's bloodstream, expressed as a percentage of alcohol by weight in a given volume of blood (for example, 0.04% by weight). It is used as a legal and medical measure of how much alcohol is currently affecting the body.
Plain English
How much alcohol is in your blood right now, shown as a small percentage. The higher the number, the more alcohol is circulating in your system and affecting your brain and body.
Context Anchor
Seen in aeromedical, fitness-to-fly, and alcohol-use discussions for pilots.
Derivation
“Level” comes from the idea of a measured line or amount. In this term, it does not mean level flight; it means the measured amount of alcohol present in the blood.
Why Pilots Care
FAA rules prohibit flying with a blood alcohol level of 0.04 percent or higher because even small amounts impair judgment, coordination, and decision-making.
Intuition Check
Do not judge blood alcohol level by how sober someone feels. It is a measured amount in the bloodstream, and the FAA limit can apply even if the person thinks they feel fine.
Example Sentence 1
Even though he had stopped drinking the night before, his blood alcohol level was still above zero in the morning, so he chose not to fly.
Example Sentence 2
Regulations require that a pilot's blood alcohol level remain under 0.04 percent for at least eight hours before operating an aircraft.