On January 20, 2022, the National Transportation Safety Board (NTSB) petitioned the FAA with a long-anticipated safety recommendation report concerning the hazards of carbon monoxide poisoning in general aviation aircraft. The NTSB requested that the FAA require active carbon monoxide detectors in general aviation aircraft, along with regular inspection of the appropriate aircraft structures and components.
In its report, the NTSB cited 31 accidents between 1982 and 2020 attributed to CO poisoning. Of the 31 accidents listed, 23 were fatal, killing 42 people and injuring another four. The report specifically highlighted two particular accidents, the first involving a Mooney and the second involving an Aeronca. For these two examples, the report included additional information and photographs showing how damaged exhaust systems were found to be the culprits for the loss of both aircraft and the souls aboard.
The document further notes in all of the accidents it cited over the study period, a CO detector was only found in one of the accidents and it was a passive version—it must be directly referenced for an indication—instead of one equipped with aural and/or visual alerts such as the Board recommends that the FAA soon require.
This most recent request is the second time that the NTSB has issued such a recommendation to the FAA and follows up on a similar petition in 2004, which was met at the time by a simple request by the FAA for operators to voluntarily comply with the NTSB recommendations. Today, the NTSB declares that the response to the original request was “inadequate to protect pilots against the hazards of CO poisoning,” necessitating the follow-up request.
In addition to specific requests made to the FAA, the NTSB also recommended that AOPA, EAA and any other similar advocacy group specifically “inform their members about the dangers of CO poisoning, encourage them to install CO detectors and ensure their aircraft exhaust systems are thoroughly inspected during regular maintenance.”
The Risk Factors
Carbon monoxide is an odorless, colorless and tasteless gaseous compound produced as a byproduct of the (incomplete) combustion of carbon-based fuels. CO is often accompanied by other combustion byproducts that can have distinctive odors, and as such, in an odd twist of fate, may have actually saved lives in the process. However, to dismiss further defensive action with a trite “I know what exhaust smells like” is dangerous and foolhardy.
From a pilot physiology standpoint, symptoms of CO poisoning can be similar to hypoxia and in other ways very different. They both center on oxygen starvation to the brain and vital organs. Unlike hypoxia, however, which is simply too little volume of oxygen in a given volume of breath due in most part to high- altitude operation, CO’s lethality comes from the poison gas actively blocking the body’s red blood cells from absorbing vital oxygen, regardless of the volume of oxygen present in the particular environment. CO can disable or kill in the air or on the ground.
Symptoms of CO poisoning have been described as “flu-like” absent the fever and, like hypoxia, it is very dangerous if not quickly detected because the deadly effects are often reached near the time that the loss of useful consciousness expires. In other words, too late to escape the danger.
Of all the aircraft designs throughout history, the worst possible configuration for a likelihood of contributing to carbon monoxide poisoning is single engine, piston driven, centerline tractor mount, enclosed cabin and, last but not least, using exhaust component heat exchangers for warming cabin air. Basically, most small aircraft. That doesn’t mean the aircraft are inherently dangerous. It just means that by falling into the highest risk design category we need to be vitally aware of the risk factors and prepare and prevent exposure accordingly.
The first defensive measure is to simply keep the airplane well inspected and maintained. Have all components of the exhaust/heat exchanger regularly inspected by qualified individuals and respect any component’s life-limit restrictions specified by either manufacturers or regulators.
Another consideration is careful attention to the firewall, especially seams and pass-throughs, where harmful vapors can enter into the cabin. A lot of sealants break down over time and can require reapplication. Concurrent with sealing bad elements out is common-sense design and usage habits for cabin ventilation. During all seasons and temperatures of conditioned air, there is wisdom in keeping a steady flow of fresh air entering the cabin. Good precautionary and checklist practices would be to turn off all conditioned air (heated or cooled) and fully open all fresh air vents at the first suspicion or alert to a cabin contamination concern. Those who still use old-school passive detectors need to incorporate those detectors in regular periodic scans of aircraft systems.
The next layer of defense, which is likely to become mandatory if the FAA follows the NTSB recommendation, is the installation of cabin detection and indication of CO presence. For most of us, our first exposure to such products was those credit card-sized indicators with the spot that would change color if an offending presence was detected. While arguably better (barely) than nothing, these “dumb” detectors must be directly viewed to be of use as they had no aural or flashing light type alert to draw attention to the danger.
More recently we have seen the development of active detectors that sound alarms when high levels of CO are detected. Variations of types of detectors have been required in most recreational vehicles for many years, especially if equipped with onboard generators. Propane detectors are common in even the most basic enclosed campers. They work in a manner similar to household smoke detectors, though the science is different because the hazardous element is different. For aircraft, there are now electronic versions that mount semi-permanently into instrument panels and even interface with modern EFIS displays for alerting purposes. The vast majority (if not all) CO detectors use a chemical reagent to detect the poison’s presence, and those reagent compounds degrade over time and must be refreshed or replaced at designated intervals. Just changing the batteries often isn’t going to keep them current. Be sure to carefully study the appropriate manuals and keep the detectors present on routine inspection checklists.
CO detectors are widely available, with different options and price points, both of which will likely change if or when the installation becomes mandatory. Whether required or not, installation of active detection is just smart and quite cheap considering the risks of noncompliance.
A Personal Note
Unfortunately, I have a personal interest in the subject of carbon monoxide poisoning. In high school I had a good friend named Rick Masters. Rick was senior class president with an elite college scholarship in hand, but he died on the very last day of high school. Late that evening, he took his girlfriend to her house, but they had a disagreement, causing her to run into her house. Ever the gentleman, Rick waited outside in the car for her to return. What neither of them knew was that he had inadvertently crimped the tailpipe of his car, perhaps by backing into a curb while turning the car around. Later, seeing that the car was still there, the girlfriend came out to find that Rick had been overcome by the toxic fumes. Just like that a stupid accident snuffed out a beautiful life full of promise and potential, and forever impacted thousands of friends and family who were shocked and saddened by the tragic event.
Recently I wrote about the loss of an acquaintance in a tragic CFIT accident in Southern California. As of this writing, there has yet to be an official determination by investigators as to the cause of that accident. However, for a highly experienced and talented pilot to fly straight into abruptly rising terrain in level flight, one should include carbon monoxide poisoning on the list of possibilities. This thought struck me powerfully when the NTSB released its safety recommendation just weeks after that accident.
All things considered, traveling in any motorized conveyance is safe. Flying in aircraft is safe and flying in Experimental/Amateur-Built aircraft is also safe. But in all ways and at all times, we must be proactively aware of potential dangers, take them seriously and actively increase the safety margins of the envelopes in which we operate. In my opinion, compliance with the recent recommendations concerning carbon monoxide prevention and active detection is a matter of common sense—whether such actions become mandatory or not. Fair winds and fresh air.