The Pilot’s Lounge #141: Killer Gas


It was to have been a quiet Friday evening at home. The weather was that chilly, misty, rain-threating mix that seems to define November, there was a crackling hot fire in the wood stove and the idea of going anywhere wasn’t the least bit inviting. The bed with its thick comforter was starting to call my name.

My cellphone rang. Until I looked at the caller ID, my reaction was one of annoyance and intent to punch the button that would decline the call. I didn’t want the outside world intruding.

It was my daughter. She lives two time zones east of me, so having her call at that hour of the evening meant something was going on that I shouldn’t ignore.

After I answered she got right to the point. She’d been called out as part of a massive search for a missing general aviation airplane. As is sadly pretty normal in such situations, there was a lot of confusion, conflicting reports from people who claimed to be witnesses and difficulty in getting hard information. She’s an EMT and, as it turned out, was the only pilot on the search team to which she’d been assigned. Her team had been unsuccessful in its attempts to get radar track data on the airplane when she called me.

She told me that ATC had had some contact with the airplane, probably a Seneca. A person on the airplane said that the pilot had had a heart attack and that a student pilot aboard was trying to land the airplane. One of the pieces of information passed on to the search teams was that the airplane had been vectored toward an airport around which search teams were spreading out. My daughter had been trying to get the dispatcher to talk to ATC and get the location of the last radar hit on the airplane and the direction it was traveling at the time. She was frustrated because no one seemed to be able to get that bit of information and was calling to see if I had any ideas.

She had an N number and asked me to see if I could pull it up on FlightAware. Her attempt showed no flights in the last three years, but she’d also been told by one source that the airplane was on an IFR flight plan and wondered if I could find anything.

She was standing outside in below-freezing weather, with light snow, and rapidly depleting her cellphone battery trying to see if a flight tracking app would be of any help.

I struck out as well. (It turned out that the airplane was not on an IFR flight plan—nor, as initially reported, a twin.)

Over the next few hours we talked briefly as she and her team walked through farm fields in central Iowa hoping to find the missing airplane. She was pleased that the search response had a lot of resources, including four helicopters, but frustrated over the lack of information available to the search teams and the inability to get the location of the last radar hit on the airplane. That brought back memories of the huge levels of confusion, misinformation and rumors that flew during the search and rescue practices I was involved with when I was in Civil Air Patrol.

Her team was pulled out of the field about 3:00 am.

A Tragic Find

After dawn, the airplane, a Piper Dakota, was spotted by the farmer on whose land it had crashed. All four occupants were deceased. Newspaper photos showed that the airplane had traveled a very short distance from the point of impact to its resting place. I suspect the impact angle was fairly steep.

I was relieved to learn that none of the scores of people involved in the search were injured or killed. That’s not always the case—we humans have a selfless streak that sometimes results in searchers getting hurt or killed trying to help others in challenging weather.

I was saddened by the tragic outcome of what had to have been a terrifying situation for the student pilot and two passengers in the airplane—a pilot becomes incapacitated just about sunset in weather that is VFR, but probably not great VFR. A student pilot must try to find an airport that may or may not be lit (I didn’t know what the situation was regarding whether there were runway lights and if they required action by a pilot to activate them and whether the student would have known how to activate them). (Full disclosure, I’m not an unbiased observer—I’ve had complete electrical system failures at night and I despise pilot-activated runway lighting systems. I think they are killers.)

What I learned some days later was even more distressing: All of the occupants had elevated levels of carbon monoxide in their blood—some sources said fatal levels (I don’t know if that’s true, the NTSB preliminary accident report only refers to “elevated levels.”) There was a two-inch crack in the muffler with sooty gray material in the muffler heat shroud and the cabin heater hose.

The Bully on Steroids

Every year there are a few accidents in which carbon monoxide poisoning is a factor. The toxic gas is odorless and colorless—and the manner in which it attacks a human makes it nothing short of a bully on steroids. Once in your lungs it combines with the hemoglobin in your red blood cells to form carboxyhemoglobin (COHb) with a bond that is 200 times stronger than oxygen’s bond on hemoglobin. CO shoves its way into your system and takes over. It puts your hemoglobin out of commission and deprives your body of oxygen. The hyper-strong COHb bond means that even tiny concentrations of CO can kill you through slow poisoning during a flight of just a few hours.

The oxygen-deprivation function of CO poisoning makes it deadly because it attacks the most important parts of your body first—brain, nervous system, heart and lungs.

To make matters worse, the deadly effects of CO exposure in an airplane are exacerbated by altitude—the normal decrease in oxygen with altitude that causes hypoxia becomes a co-combatant with the COHb bond to disable and then kill you.

The first symptoms are headache, fatigue, dizziness, vision problems, increased pulse and respiration rates and nausea. Not one of those effects is a prescription for enhanced flying skills and judgment.

I shudder to think about what the student pilot was going through as he tried to save the flight while his faculties were progressively robbed from him by the killer gas.

Adding a nasty twist to depriving you of oxygen while you are being exposed to CO, that mega COHb bond means that the CO remains firmly in place a long time even after you’ve gotten away from the source. Once you start breathing uncontaminated air, the half-life of COHb is five hours. Think of it—you somehow manage to land, park the airplane and crawl out the door with a COHb saturation of 50 percent. In five hours, it will be down to 25 percent—that’s still a big-time exposure. If you breathe pure oxygen, the half-life drops to two hours, still not a rapid re-oxygenation of the body. In severe exposure events, the victim is placed in a hyperbaric chamber with pure oxygen under three atmospheres. Even then, COHb hangs on—the half-life becomes a half hour.

Protect Yourself

The data I’ve seen shows that the risk of an accident due to CO poisoning is slightly less than that of a midair collision. However, I strongly suspect that a fair number of pilots have experienced CO poisoning and torn up an airplane on landing, survived and did not get tested for CO poisoning. I also am of the opinion that more than a few have been poisoned, landed without breaking anything while feeling strange and didn’t get tested for CO poisoning. I suspect that if the numbers were available, the true rate of CO poisonings in little airplanes, especially ones that are a few years old, would be shown to be much higher than the rate of midair collisions.

We pay good money for devices that will warn of a risk of a midair. Good-quality CO detectors cost less. It seems to me that there isn’t an excuse for not having at least a portable CO detector in your airplane that will give you an effective warning when even low levels of CO are present. Low levels are dangerous because the body doesn’t shed the toxin rapidly, so the effects multiply. The device has to have an effective warning system—a warning that doesn’t get your attention is worthless. You’ve got to know of a risk to act on it.

Some CO Detectors

I did a review of CO detectors in the October 2016 issue of our sister publication, Aviation Consumer. The takeaway I got from researching the article was three-fold: 1) A CO detector should read out CO levels from 1 PPM (part per million) up, so that you can spot-check areas in the cabin (surprisingly, the baggage and rear seat areas are notorious for CO because CO can come into the tailcone where the air flow is forward into the cabin and the baggage curtain often doesn’t seal well enough to keep the air from coming into the cabin; 2) A CO detector should sound a loud warning when the level hits about 35 PPM because of the cumulative risk of exposure to relatively low levels of the gas; and 3) The stick-on chemical “spot” detectors that have a circular chemical patch that is advertised to turn “dark” in the presence of CO are, in my opinion, nearly worthless.

Get One

I’ve been flying with various portable low-level CO detectors for several years. Turning the unit on before startup and off after shutdown is part of the checklist. There are three that I recommend because I’ve flown with them and tested them in the presence of CO. In my opinion, they work well, have a loud alarm and detect very low levels of CO.

The Tocsin OI-315 CO Monitor by Otis Instruments is available for $169.95 at Sporty’s. It alarms at 35 PPM, with a flashing LED light, 90 dB Piezo horn and the thing vibrates. It has a belt clip, mounting ring and hook and loop tape so it can be mounted almost anywhere. The low-level alarm can be silenced. At 100 PPM it activates a high-level alarm that can’t be silenced except by moving the unit to a fresh air location and shutting it off. I think that’s a potential distraction, but not a deal-killer. For several years that was the unit kept in an airplane I shared with two other owners.

The CO Experts ULTA is the most sophisticated of the portable units I’ve found. It’s available for $199 from Aeromedix. I’ve owned two CO Experts units, using one for the house and one that I’d pull out of the flight bag and use in rental airplanes. Its Piezo alarm sounds at 85 dB. The first alert is at 7 PPM. The type of alert changes as the concentration level rises. It has a memory feature that can be helpful to medical personnel to show the history of exposure. It also has a warning silence feature, which I used one year when holding for a long time for an instrument clearance from AirVenture in a twin. The wind from the left blew enough exhaust from the left engine through the open vent window in the cabin to trigger the alarm.

The Pocket CO 300 ($131.95 from Aircraft Spruce) is the unit I’m using now. It’s a keychain CO detector. It doesn’t alarm until 50 PPM—a little high, in my opinion—setting off an 82-dB warning, LED light and vibration with increasing frequency at thresholds of 125 and 400 PPM. It has a replaceable coin cell battery. My airplane keys are on the unit and I turn it on when I put the key in the ignition—off at shutdown.

I suggest that you stay away from the chemical spot detectors. To start with, you have to have keep it in your panel scan to see if it is giving you a warning. Worse, each type has a life limit—but pilots seem to stick them on the panel and leave them forever. Beyond that, for the ones that turn “dark,” what is “dark”? How do you tell “dark” when you’re flying at night? (It was cold, it was dark, I was alone … precisely the time you need a CO detector with an effective warning.) The one we tested at Aviation Consumer didn’t change color until CO hit 90 PPM; way too high, in my opinion. They are cheap, and pilots have a reputation for being tightwads—so they buy something that is probably not going to be effective and fly away with a false sense of security. Do you really want to be that pilot?


My daughter’s involvement in an ultimately tragic search for a missing airplane triggered my thoughts of the need for carrying an effective CO monitor in the airplanes we fly. I think that the level of risk involved combined with the price of an effective detector make buying and using one in an airplane worthwhile. I’m also going to check the battery on my keychain unit when I get up from this computer.

Rick Durden is a CFII, holds an ATP with type ratings in the Douglas DC-3 and Cessna Citation and is the author ofThe Thinking Pilot’s Flight Manual or, How to Survive Flying Little Airplanes and Have a Ball Doing it, Vols. 1 & 2.