General aviation is civilian, non-commercial flight. It applies to sport aviation, business travel, humanitarian aid, agriculture, environmental conservation, and bush flying.
The most common sources of carbon monoxide in general aviation are exhaust gases from piston-driven engines.
There are, however, other sources relevant to the wider sector including the exhaust gases from turbine engines, auxiliary power units, airside vehicles, ground servicing equipment and from combustion of materials during emergencies.
Should these gases find ingress into the aircraft interior they may come into contact with crew or passengers. The resulting symptoms can vary from nothing noticeable to, in the worst cases, a catastrophic accident with the potential for significant loss of life and collateral damage.
Carbon monoxide poisoning is a significant concern in general aviation. In 2020 the CO Research Trust commissioned Queen Mary's University of London to write a White Paper.
The White Paper was titled "Carbon monoxide poisoning in the UK's light aircraft fleet".
The paper sought to assess the status, best practices and risks associated with carbon monoxide poisoning across the UK’s aviation sector.
The primary deliverable was to further understand the pertinent issues of carbon monoxide poisoning with a focus on general aviation.
Dr Andrew Spowage, one of the authors of the paper at Queen Mary's University of London, presented the project during one of the Trust's lectures.
The paper found that in the general aviation industry, the common sources of carbon monoxide exposure are:
• Aircraft turbine engine exhaust system
• Piston-powered aircrafts
• Auxiliary power units (exhaust system)
However, the majority of the aircraft accidents related to carbon monoxide exposure are directly linked to piston powered aircrafts.
The Federal Aviation Administration (FAA) estimates that between 1967 to 1993, 360 victims of air crashes suffered from exposure to carbon monoxide which impaired their cognitive abilities.
Although the report only highlights the summary of a few aircraft accidents related to carbon monoxide poisoning, the majority of the report points out certain areas of concern with piston powered aircrafts.
These are listed below:
Exhaust System Obstruction
Any obstruction in the exhaust muffler or any other components of the exhaust system can cause tubes to burn, hot spots in the system, or the weakening of heat transfer pins. This could allow carbon monoxide to leak into the cabin of the aircraft.
Waste Gate Carbon Accumulation
The waste gate in an aircraft vents the exhaust to prevent over-pressurisation. Excess carbon build-up can cause the gate to become inoperable, or the valves to stick.
Heat Exchanger Crack
Heat exchangers are made of metals that contract while in use. Constant use could result in cracks. A crack in the heat exchanger can allow carbon monoxide to leak from the exchanger into the aircraft cabin. This is perhaps the most common carbon monoxide leakage scenario.
Engine Vibration
Vibration from the engine at varying rates can cause metal fatigue. This could compromise welded areas, joints or even the heat exchanger.
Exhaust Corrosion
Thermal fatigue and metal deterioration can compromise the parts of an exhaust system. This could be a resultant effect of high temperature and corrosive engine exhaust.
To read more about this project click here.
In this article, CO Research Trust CEO Adrian McConnell discusses whether or not carbon monoxide poisoning in general aviation is a preventable problem.