Definition
A toxic condition caused by inhaling carbon monoxide, an odorless, colorless, tasteless gas produced by the incomplete combustion of fuel. CO binds to hemoglobin in the blood roughly 200 times more readily than oxygen, displacing oxygen and preventing its delivery to body tissues. The result is a form of hypemic hypoxia in which the blood is physically present and circulating but cannot carry adequate oxygen. Symptoms include headache, dizziness, drowsiness, nausea, impaired judgment, and eventually loss of consciousness or death.
Plain English
Breathing in carbon monoxide makes your blood unable to carry oxygen properly. Even though you're breathing normally, your body slowly starves of oxygen, and you may not realize it's happening until you're already impaired.
Context Anchor
Pilots most often think about CO poisoning when using cabin heat, checking for exhaust leaks, or investigating unexplained headache, dizziness, sleepiness, or confusion in flight.
Derivation
Carbon monoxide gets its name from carbon plus monoxide, meaning one oxygen atom bonded to one carbon atom. The 'mono-' (Greek for 'one') distinguishes it from carbon dioxide, which has two oxygen atoms. The dangerous version is the one with less oxygen — easy to remember because it's also the one that takes oxygen away from you.
Why Pilots Care
It can produce subtle symptoms such as headache or drowsiness that impair judgment and may progress to unconsciousness, especially at altitude in piston aircraft with heater or exhaust leaks.
Grounding Statement
A pilot can be breathing normally and still be starved of oxygen because carbon monoxide is blocking the blood from carrying it.
Intuition Check
Do not assume you will smell or see the problem. Carbon monoxide is colorless and odorless, so CO poisoning may first show up as how you feel or how clearly you are thinking.
Example Sentence 1
After noticing a headache and dizziness shortly after turning on the cabin heat, the pilot suspected CO poisoning, shut off the heater, opened the fresh air vents, and landed at the nearest airport.
Example Sentence 2
Preflight inspection of the exhaust system helps reduce the risk of CO poisoning during winter flights.