Silent Killer: Carbon Monoxide (CO) in the Cockpit
Most small airplanes use a heat muff around the muffler for heat in the cockpit. Fresh air is piped into the heat muff. The heated air is ducted into the cockpit as needed.
This system works well, provided exhaust gases do not become part of the heated air. If that happens, carbon monoxide (CO) enters the cockpit. Even small concentrations of that deadly gas can incapacitate pilots and passengers. Thus, great care must be taken to prevent this disaster.
There are other ways CO may enter the cockpit: for example, due to a flawed design of the exhaust system where in a certain attitude CO may enter a fresh-air intake. We had this problem originally in our plane during steep angles of attack. A redesign of the exhaust system solved the problem.
The publication Detection and Prevention of Carbon Monoxide Exposure in General Aviation Aircraft by the Federal Aviation Administration has an in-depth discussion of the CO hazard. Here, we shall not repeat that material, but summarize some of the ideas and include a recommendation.
During the annual inspection, the heat muff is removed, and the entire exhaust system is carefully examined for damage and leaks. Also, the hoses supplying cold air to the heat muff and piping heated air to the cockpit, as well as all connecting hardware are scrutinized for damage.
Since this inspection is done once a year, we are not really sure during the rest of the year that a leak has not recently developed. Hence, it is good practice to inspect the exhaust system, heat muff, and hoses once more at the start of fall weather when we typically begin use of the heater.
Despite all these precautions, there still is a small probability that the system fails and disastrous CO poisoning happens.
The best tool to warn about that rare event is a CO detector in the cockpit. There are several choices.
Aircraft supply stores provide portable or panel-mounted detectors, with price ranging up to hundreds of dollars. The detectors have digital displays that show the level of CO in the cockpit. In our experience, many aircraft in the homebuilt experimental category do not have such a detector due to its substantial cost.
Also available are placards with a colored dot that darkens when CO is present. They work for a specified period, typically 3 months, and are popular due to their low cost.
The above study is rather critical of placard detectors for a number of reasons. In particular, the placard does not tell the CO level, and thus the pilot does not know whether drastic action must be immediately taken or a more deliberate remedy suffices.
Thus, it might seem that the only correct choice is one of the expensive digital units. But there is a low-cost alternative.
Stores such as Sears and Walmart, hardware stores, and a number of on-line stores offer CO detectors that are small, light-weight, operate solely on batteries, and have digital displays showing CO level. Several of them are low-cost, the batteries need replacement just once a year, and overall life of the unit is several years.
One such unit has been our choice. It is manufactured by Kidde, model number KN-COPP-B-LPM. It has a digital display, weighs 6.5 ounces, operates for one year on three AA batteries, has a life of 7 years, and can be bought for less than $30.
We tested the unit outside our house in the vicinity of a running lawn edger, where it immediately picked up CO presence: farther away at 40 ppm, and within 10 ft up to 700 ppm, which is a huge concentration. By the way, this says something about the health hazards of lawn equipment.
After the test with the lawn edger, we moved the unit into the house. After a short while, the CO level rose temporarily to 15 ppm. At that time, the edger had been shut off for several minutes, and we just had come in from the outside.
Apparently, a faint whiff of the exhaust gases still lurking outside managed to move into the house as we walked in and triggered the reading. Afterwards, the CO level stayed in the house at 0 ppm.
We recently repaired the heat muff of our plane and replaced the hoses. During the first flight, we carried out all sorts of maneuvers, turned the heater off and on, and throughout had a reading of 0 ppm in the cockpit, a reassuring fact.
The message is this: Given the availability of low-cost, light-weight, battery-powered, and low-maintenance detectors with digital display, there is little excuse for not having such a unit along. It might save lives you care about, such as yours.
This system works well, provided exhaust gases do not become part of the heated air. If that happens, carbon monoxide (CO) enters the cockpit. Even small concentrations of that deadly gas can incapacitate pilots and passengers. Thus, great care must be taken to prevent this disaster.
There are other ways CO may enter the cockpit: for example, due to a flawed design of the exhaust system where in a certain attitude CO may enter a fresh-air intake. We had this problem originally in our plane during steep angles of attack. A redesign of the exhaust system solved the problem.
The publication Detection and Prevention of Carbon Monoxide Exposure in General Aviation Aircraft by the Federal Aviation Administration has an in-depth discussion of the CO hazard. Here, we shall not repeat that material, but summarize some of the ideas and include a recommendation.
During the annual inspection, the heat muff is removed, and the entire exhaust system is carefully examined for damage and leaks. Also, the hoses supplying cold air to the heat muff and piping heated air to the cockpit, as well as all connecting hardware are scrutinized for damage.
Since this inspection is done once a year, we are not really sure during the rest of the year that a leak has not recently developed. Hence, it is good practice to inspect the exhaust system, heat muff, and hoses once more at the start of fall weather when we typically begin use of the heater.
Despite all these precautions, there still is a small probability that the system fails and disastrous CO poisoning happens.
The best tool to warn about that rare event is a CO detector in the cockpit. There are several choices.
Aircraft supply stores provide portable or panel-mounted detectors, with price ranging up to hundreds of dollars. The detectors have digital displays that show the level of CO in the cockpit. In our experience, many aircraft in the homebuilt experimental category do not have such a detector due to its substantial cost.
Also available are placards with a colored dot that darkens when CO is present. They work for a specified period, typically 3 months, and are popular due to their low cost.
The above study is rather critical of placard detectors for a number of reasons. In particular, the placard does not tell the CO level, and thus the pilot does not know whether drastic action must be immediately taken or a more deliberate remedy suffices.
Thus, it might seem that the only correct choice is one of the expensive digital units. But there is a low-cost alternative.
Stores such as Sears and Walmart, hardware stores, and a number of on-line stores offer CO detectors that are small, light-weight, operate solely on batteries, and have digital displays showing CO level. Several of them are low-cost, the batteries need replacement just once a year, and overall life of the unit is several years.
One such unit has been our choice. It is manufactured by Kidde, model number KN-COPP-B-LPM. It has a digital display, weighs 6.5 ounces, operates for one year on three AA batteries, has a life of 7 years, and can be bought for less than $30.
We tested the unit outside our house in the vicinity of a running lawn edger, where it immediately picked up CO presence: farther away at 40 ppm, and within 10 ft up to 700 ppm, which is a huge concentration. By the way, this says something about the health hazards of lawn equipment.
After the test with the lawn edger, we moved the unit into the house. After a short while, the CO level rose temporarily to 15 ppm. At that time, the edger had been shut off for several minutes, and we just had come in from the outside.
Apparently, a faint whiff of the exhaust gases still lurking outside managed to move into the house as we walked in and triggered the reading. Afterwards, the CO level stayed in the house at 0 ppm.
We recently repaired the heat muff of our plane and replaced the hoses. During the first flight, we carried out all sorts of maneuvers, turned the heater off and on, and throughout had a reading of 0 ppm in the cockpit, a reassuring fact.
The message is this: Given the availability of low-cost, light-weight, battery-powered, and low-maintenance detectors with digital display, there is little excuse for not having such a unit along. It might save lives you care about, such as yours.
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