Ed Hicks
28 August 2024
From $139 and $169 (2022 prices)
Carbon Monoxide (CO) is bad news, but then again, you know that as you learned about it in your Human Performance groundschool studies. So given we know it’s so bad for us, and that aircraft engine exhausts and cabin heaters are notorious for trying to kill us so covertly, why then do so many pilots continue to put their trust in those stick-on plastic chemical dot detector cards? I know they’re cheap, but life is precious, right?
You can’t see CO, it has no taste nor smell, and it competes with oxygen by binding to the haemoglobin in your red blood cells. Your haemoglobin even works against you, as its affinity for CO is 210 times greater than that for oxygen, plus its effects are cumulative. The effects of CO, measured in parts per million (ppm), depend on concentration and length of exposure, as well as the health condition of each individual. The maximum continuous exposure for an adult in any eight-hour period is considered to be 35ppm.
Most people won’t experience any symptoms from prolonged exposure to CO levels of approximately 1-70ppm, but some heart patients might experience an increase in chest pain. As CO levels increase and remain above 70ppm, symptoms become more noticeable and can include headache, fatigue and nausea. At sustained CO concentrations of 200ppm, dizziness will occur, 400ppm is life threatening after three hours, while at 800ppm, you’ll be unconscious within two hours, and likely dead within three.
Collectively, this means that it’s worth investing in an active CO detector, such as the two that I’ve tested.
The AV8 Inspector and the AV8 Inspector Pro are small stand-alone devices that you can take along in the cockpit easily. Both have an LCD display which displays a live readout of CO gas concentration from 0-1,999ppm, as well as an audible alarm buzzer. Both units also have a MAX mode, which will show the highest peak reading measured while the MAX mode is active. The display will only show another value once a new higher reading is encountered.
A neat mounting bracket is included with both units, or you can use the clip on the back of the unit, although it really only works for attaching the device to something such as a fabric pocket, given that it’s a fairly tight closing device with sharp triangular teeth. Just place with caution if you do use it!
The Pro is slightly more expensive and includes a vibrating alarm, offers adjustable high and low alarm setting thresholds and a time-weighted average option. This means it can display the maximum eight-hour average CO reading in the last 24 hours. The factory defaults for both units are a low setting of 35ppm, and 200ppm for high alarm.
On the Pro, you can change them – simply hold the power and Max buttons when the unit is switched on for five seconds and a menu screen will appear, then you just scroll through to find the appropriate setting page.
I took the units flying in the RV-3 and in the Vagabond. The RV-3 surprised me by providing a very CO-free cockpit environment, even with the cabin heater pulled on. It was 0ppm throughout the entire flight.
Previously, when I tested active CO detectors in our Summer 2019 issue, the FLYER 182 cabin had shown an ambient CO level during cruise of around 2ppm, while pulling on the cabin heat saw an increase to 8-10ppm. So it was surprising to have such a clean cockpit environment.
The Vagabond was a different story though. With both units clipped to the right-hand side door pocket, as I taxied out with the door shut and the cabin heat off, the readings on both were around 10ppm.
Once airborne, both units peaked around 65ppm on climb-out, before settling to 50ppm during cruise. This triggered the LO alarms on both units. Four lights flash on the unit, and they are clear to see. The audible buzzer (80-85dB) was not that obvious in flight, although I was able to hear it clearly with the power pulled back to 1,200rpm when flying base leg.
If you were wearing the Pro unit on a shirt pocket, the vibrating alarm might likely be a bonus alert if cabin noise overwhelms the alarm.
Turning the cabin heat on seemed to make little difference, which I’ll confess was a surprise, as I was expecting something. What did catch my attention was while the cabin heat was pulled on, about five seconds after deselecting a good blast of carb heat, the units peaked at 83 and 105ppm for about 15 seconds.
Interestingly, a repeat of the carb heat / cabin heat combo, with one unit on the left side of the cockpit and one still on the door pocket, showed that the high readings seemed to be focused around the right side of the cabin. The same happened if I held a unit down towards my feet, near the cabin heat outlet, which made me think that a combination of gaps around the right door, and a right side exhaust outlet might be the biggest CO issue in the Vagabond cockpit.
Regardless, we’ll certainly be giving the Vagabond exhaust system a good check over as part of her winter maintenance, and take a look at better sealing around the door. One thing is sure though, the old school CO card detector we’ve carried in the past never gave us a clue to any of this.
Based on my testing, if you have an aircraft where the cockpit has an ambient level of around 50ppm of CO, then paying extra for the Inspector Pro is worth it for being able to set your own alarm threshold levels, otherwise the preset low alarm setting could see it being triggered frequently. That said though, I’m sure we all aspire to make our cockpit environments as CO-free as possible.
Something to be aware of, the manufacturer recommends that you calibrate the AV8 Inspector every six months to ensure the best accuracy possible, and an End of Life (EOL) symbol will display in the unit after two years (end of the warranty period).
However, the instructions advise that a successful calibration will remove the EOL notification for an additional 180 days. Future successful calibrations can continue as long as the electromechanical sensing element remains in good condition. One of the calibration methods is a fresh air ZERO cal, the other is a more involved GAS cal using 50ppm calibration gas.
UPDATE 28 August 2024: The CAA is making active carbon monoxide detectors mandatory in single-engine piston aircraft. See here
There’s no question that carrying an active CO monitor in the cockpit is a useful and potential life-saving measure, plus if you’re in and out of various cockpits, an easily portable one like the AV8 Inspector is a useful tool to measure how these environments vary in the level of CO hazard we can be exposed to.
