Of all the hazards that general aviation pilots face, carbon monoxide poisoning is among the most dangerous precisely because it is the hardest to recognise. Unlike engine failure or icing, CO poisoning doesn’t announce itself with a dramatic symptom — it gradually impairs your judgment and physical capacity in ways that can feel remarkably similar to simple fatigue, leaving you less able to recognise that something is wrong just as the situation becomes most dangerous.
How CO Enters the Cockpit
In piston aircraft with cabin heating systems, the most common source of cockpit CO is a cracked exhaust heat exchanger. The cabin heat system works by routing cabin air over the exhaust system — if the exhaust develops a crack or leak, combustion gases including CO can enter the airstream that heats the cabin. Leaks can develop gradually and may not be visible during a preflight inspection.
Other sources include exhaust leaks elsewhere in the system, deteriorated exhaust gaskets, and — in some configurations — exhaust fumes entering through openings in the firewall or fuselage. Older aircraft are at higher risk due to age-related deterioration of exhaust components, but CO risks exist in any aircraft with an internal combustion engine.
Symptoms: What to Watch For
Carbon monoxide binds to haemoglobin in the blood approximately 200 times more readily than oxygen, progressively reducing the blood’s ability to carry oxygen to the brain and other organs. Early symptoms include:
- Headache — often the first and most reliable early indicator
- Fatigue and drowsiness — frequently attributed to a long flight or early start
- Nausea or dizziness
- Difficulty concentrating or confusion
- Visual disturbances
The insidious aspect is that as CO levels rise, the impairment of judgment makes it increasingly difficult for the affected pilot to recognise that something is wrong. A pilot in the early stages of CO poisoning may feel only mildly unwell — and may rationalise that feeling rather than treating it as an emergency.
What to Do If You Suspect CO Poisoning In Flight
The response to suspected in-flight CO exposure is immediate and straightforward:
- Turn off cabin heat immediately
- Open fresh air vents and any available fresh air sources
- Use supplemental oxygen if available
- Declare an emergency and land at the nearest suitable airport
- Do not continue the flight to your planned destination
Prevention: The CO Detector
The simplest and most effective protection against in-flight CO exposure is a carbon monoxide detector mounted visibly in the cockpit. Basic electrochemical spot detectors are inexpensive and change colour in the presence of CO. More sophisticated digital detectors provide quantitative CO readings and audible alarms. Many pilots treat these as non-negotiable items in their aircraft — as important as a fire extinguisher.
Annual inspections should include a thorough examination of the exhaust system, heat exchanger and associated plumbing. If your mechanic finds any cracks or deterioration in the exhaust system, the repair should be completed before the next flight. CO exposure is an airworthiness issue, not a comfort issue.
