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How A Cracked Muffler Caused A Fatal Accident

As some of the coldest temperatures in recent history pass through the United States, you'll probably use your airplane's heater extensively. Here's how cracks in your muffler could cause in-flight carbon monoxide poisoning.

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Carbon Monoxide Incapacitates Pilot

We found the following report in the NTSB's Accident Database after a pilot using his airplane's heater crashed into the ground after becoming incapacitated.

"The pilot was returning to his home airport. A review of radar data showed the accident airplane in a straight-line descent from cruise flight at a rate of nearly 2,900 ft per minute. The descent resulted in a loss of 8,100 ft in less than 3 minutes until the airplane disappeared from radar in the vicinity of the accident site. Disassembly of the airplane's cabin heat shroud, which provided heated air to the cabin, revealed evidence of cracks and holes in the muffler wall and exhaust gas penetration into the interior of the shroud. According to the autopsy report, the pilot died as a result of thermal injuries and smoke inhalation, with soot present in the upper airway and 37% carbon monoxide found in his blood postmortem. Based on the lack of soot in the lower airway and the elevated carbon monoxide levels, the majority of the carbon monoxide in the pilot's blood was likely from inhalation during the flight at levels that would have impaired his ability to safely fly the airplane."

NTSB Probable Cause: "A defective exhaust system that allowed carbon monoxide to enter the cabin and impair the pilot, rendering him unable to control the airplane."

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How It Happened

Most small single-engine aircraft cabins are heated by passing outside air over the muffler, and then passing that heated air into the cabin. Most of the time that's not a problem, because the exhaust air and cabin air never mix. But, if the muffler is cracked, it can cause serious problems.

If you have a cracked muffler and you have your heater on, carbon monoxide can start entering the cabin. And if that happens, your first signs of carbon monoxide poisoning will most likely be these symptoms:

What To Do If You Think You Have Carbon Monoxide Poisoning

So what should you do if you start feeling the symptoms of carbon monoxide poisoning? First off, always follow your checklist, but what you'll find is most of them are very similar:

Step 1 - Turn Off The Cabin Heat

By turning off the heat, you're preventing any more toxic air from entering the cabin. But even though you've stopped the source, your cabin is still filled with CO gas.

Step 2 - Open Your Fresh Air Vents

Airplanes differ, but almost every airplane has one or multiple fresh air vents. They might be controlled on the panel, or they might be controlled near the floor or ceiling of your plane. Either way, get them all FULL OPEN. It might get cold quickly, but you're pumping fresh air into the cabin, and dumping the bad air out the back.

Step 3 - Open Your Cabin Windows

This isn't possible in all airplanes, but in many of them you can open the windows. This simply helps step 2 in getting more fresh air into the cabin.

Step 4 - Land As Soon As Practical

Find an airport near you and land. And keep in mind, your judgment and motor skills are impaired when you have carbon monoxide in your bloodstream, so you need to be extremely careful when choosing your landing spot, as well as flying yourself there.

Step 5 - Tell ATC

ATC may be able to help with vectors to an airport, and they can also coordinate medical help on the ground once you've touched down.

Step 6 - Get Medical Attention

Just because you're on the ground doesn't mean you're in the clear. It takes up to 4-6 hours for your body to exhale 50% of the carbon monoxide that you inhaled.

Stop Carbon Monoxide Before It Leaks

According to the NTSB, you should inspect exhaust systems, air ducting, firewalls, and door/window seals thoroughly at every 100-hour or annual inspection to reduce the chance of CO being introduced into the cockpit. You should also inspect heater air inlet cockpit vents for evidence of sooting, consistent with the presence of CO.

On preflight, take a few seconds to closely scan your muffler and heater shroud for cracks. For just $5 you can buy a Carbon Monoxide Detector from Sporty's Pilot Shop to keep in your airplane.

Swayne Martin

Have you ever experienced carbon monoxide in the cockpit? Tell us about it in the comments below.

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and an Embraer 145 First Officer for a regional airline. He graduated as an aviation major from the University of North Dakota in 2018, holds a PIC Type Rating for Cessna Citation Jets (CE-525), and is a former pilot for Mokulele Airlines. He's the author of articles, quizzes and lists on Boldmethod every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures on his YouTube Channel.

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