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Carbon Monoxide: A Hidden Killer

by Paul Engstrom, Aviation Writer and IFA Member

Any one of numerous blunders that the pilot of a Piper Cherokee made on a mid-winter night in Minnesota would have been enough to doom his flight.

But what ultimately killed him and his passenger was carbon monoxide poisoning.

On January 26, 1998, the pair were flying in fog and mist from Brainerd to Owatonna. The pilot had all of three hours of instrument and about six hours of night experience under his belt, none of it solo.

And, according to the National Transportation Safety Board's accident report, the Cherokee's muffler'despite an inspection just two months earlier'was rusty and pocked with tiny holes, allowing carbon monoxide from the engine's exhaust to enter the cockpit.

Indeed, an autopsy revealed that the pilot had a carboxyhemoglobin level of 24 percent. Translation: Nearly one-fourth of all the oxygen-carrying hemoglobin in his red blood cells was bound instead to carbon monoxide, depriving his brain and body of life-giving oxygen.

There are good reasons why carbon monoxide deserves a prominent place in the Hall of Blame when it comes to insidious general-aviation hazards:

  • The gas, a byproduct of incomplete combustion, is odorless, colorless, and toxic even in small amounts.
  • Symptoms of carbon monoxide poisoning'nausea, fatigue, headache, dizziness, and vision problems, among others'may be mistaken for a cold, the flu, or indigestion.
  • You're more susceptible if you smoke (in which case your carboxyhemoglobin level already is 3 to 10 percent), you're old, or not physically fit.
  • Carbon monoxide bonds with hemoglobin 200 times more readily than oxygen does, essentially bumping oxygen from its seat in the bloodstream.

A number of sources may be to blame for carbon monoxide exposure. Possible culprits are a crack in the heat muff or shroud on the exhaust system that feeds the cabin heater, a leak between the engine compartment and cockpit, a faulty exhaust-manifold gasket, even exhaust from the aircraft taxiing ahead.

'Any leak in the exhaust system of an aircraft is a real and present danger,' says Dr. Robert W. Carlson, an instrument-rated pilot and professor of medicine at Stanford University.

Does this mean pilots are at the mercy of carbon monoxide? No. But it does mean paying special attention to the 'P' word' prevention. Namely:

  • Ensure the muffler is thoroughly examined by mechanics at every 100-hour inspection. In the case of the Piper Cherokee, the NTSB faulted mechanics for an 'inadequate' muffler check.
  • Abide by the Federal Aviation Administration's airworthiness directives, if any, regarding your exhaust system.
  • Consider installing a carbon monoxide detector in the cockpit. But beware: Not all detectors live up to manufacturers' claims and some have a short life span.

Fortunately, you can quickly and easily counteract carbon monoxide exposure aloft. Simply turn off the cabin heat, open the fresh-air vents or use supplemental oxygen if you have it, and get on the ground as soon as possible.

When he isn't flying, Paul Engstrom writes and edits from Sebastopol, Calif.

The information contained herein is meant for informational purposes only. Neither IFA, nor Paul Engstrom assume any responsibility or liability for events that occur due to actions you or others on your behalf take based on the information given in this article. You are proceeding at your own risk. It is strongly advised that you seek the opinion and advice of a qualified aviation medical examiner and appropriate medical physician for any medical needs you may have.