But pilots can also be impacted by much lower levels. It's highly likely you have an exhaust leak. Certainly a concentration of 200 ppm should get your attention right away: turn off the heat, open the fresh air vents, and consider landing. In our experience, pilots should err on the side of caution. OSHA uses 200 ppm as a 5-minute sample ceiling, and 1500 ppm as an instantaneous limit. So how much is too much? The US Occupational Safety and Health Administration (OSHA) uses 35 ppm as its lower limit, although it's important to note that this is based on a time weighted average (TWA), taken over 8 hours. All CO detectors measure concentration in parts per million (ppm), and alert pilots with some combination of lights, audio alarms, and even vibration. In fact, the NTSB now strongly suggests that all airplanes have some type of CO detector on board. If you buy a quality device and make it part of your regular checklist, you're much more likely to detect a leak before it becomes a major problem. The easiest thing to do is use a carbon monoxide detector on every flight. Since much of this is hidden with the engine cowl on, have your mechanic do a thorough inspection of all exhaust parts at every oil change and annual, too. Look for any cracks, holes, or hot spots, which might indicate a leak. One way to avoid this scenario is to perform a good preflight inspection every time you fly, paying particular attention to the condition of the exhaust system. It was only because I had a good CO detector that I stayed out of the NTSB reports. A crack in the exhaust sytem of the helicopter I was flying meant unfiltered exhaust gasses were pouring into the cockpit every time I pulled the cabin heat knob. In fact, I narrowly avoided one myself a few years ago. ![]() Worst of all, your brain won't notice anything is wrong-if you don't have some way to monitor CO in the airplane, you might never know it's there. At low levels, that might mean just a headache, but over a long enough period of time or with high enough CO concentrations, that might mean impaired decision-making or even incapacitation. With enough exposure, this can lead to symptoms of hypoxia (anemic hypoxia, specifically). ![]() This is dangerous because CO essentially tricks your blood into bonding with it instead of oxygen, starving your body of what it needs. Unfortunately, a leak in the exhaust system means carbon monoxide (CO), a colorless, odorless, tasteless-and potentially deadly-gas, can enter the cabin. Most light airplane heaters use a shroud around the exhaust to warm ambient air, which is a simple and effective way to keep pilots and passengers warm. Here's what pilots need to know about carbon monoxide: where it comes from, how to prevent it from entering the cockpit, and what tools are available for detecting it.
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