Definition
A colorless, odorless, tasteless gas produced by the incomplete combustion of fuel. When inhaled, it binds to hemoglobin in the blood far more readily than oxygen, reducing the blood's ability to carry oxygen to body tissues, including the brain and eyes. In aircraft, it can enter the cabin through a cracked exhaust manifold or a leaking heater shroud, since most piston-engine cabin heaters draw warm air across the exhaust system.
Plain English
A poisonous gas you cannot see, smell, or taste. It cuts off the oxygen supply your body needs, even though you keep breathing normally. In small aircraft, it most often sneaks into the cabin through the heater.
Context Anchor
Seen in night flying, cabin heat, exhaust leak, and pilot health discussions, especially because reduced oxygen affects night vision early.
Derivation
From Latin carbo (coal, charcoal) and Greek monos (one) plus oxys (sharp, acid -- the root of oxygen). Literally 'one carbon, one oxygen.' The 'one oxygen' part is what makes it dangerous: a normal, safe combustion product is carbon dioxide (two oxygens). When combustion is incomplete, you get this short-an-oxygen version instead.
Why Pilots Care
Exposure causes gradual impairment of night vision, judgment, and coordination that can lead to spatial disorientation or loss of consciousness without obvious warning signs.
Grounding Statement
On a cold night with cabin heat on, a small exhaust leak can let carbon monoxide enter the cabin while everything still looks and smells normal.
Intuition Check
Do not assume carbon monoxide will smell like smoke or fuel. The danger is that it is invisible and odorless, so symptoms or a detector may be the first warning.
Example Sentence 1
After noticing a headache and slight nausea on a cold cross-country flight, the pilot suspected carbon monoxide and immediately shut off the cabin heater and opened the fresh air vents.
Example Sentence 2
Even low levels of carbon monoxide can reduce night vision before the pilot notices any physical symptoms.