Plane & Pilot
Friday, October 1, 2004

The Silent Killer

The NTSB’s latest safety recommendation targets the dangers of carbon monoxide leaks caused by defective exhaust systems

Against the background of an aging fleet of general-aviation, piston-powered airplanes, the NTSB suggested that it’s time for the Federal Aviation Administration (FAA) to take a closer look at engine mufflers and do more to eliminate potential hazards posed by mufflers that have deteriorated. So on June 23, the NTSB issued a safety recommendation to the FAA dealing with the subject. NTSB safety recommendations often are the first step along the path leading to FAA regulatory edicts, such as airworthiness directives.

In its recommendation, the NTSB expressed that although it’s routine for engine-exhaust systems to be periodically examined using visual inspection or pressure testing when called for, defects sometimes go unnoticed. Cracks and pinholes can allow carbon monoxide (CO) and other exhaust gases to leak into the cabin, causing one part of CO per 20,000 parts of air to seep into a person’s system.

The effects are dangerous. They include shortness of breath, headache, fatigue, nausea, disorientation, unconsciousness and, ultimately, death. In addition, hot exhaust gas escaping from a bad muffler or other part of the exhaust system into the engine compartment can damage hoses, wires and other components.

The recommendation revealed that the NTSB examined its own accident database and found that over the last 30 years, there were 125 accidents or incidents involving muffler failure on single-engine, piston airplanes that resulted in 42 fatalities and 27 serious injuries. When the NTSB looked for accidents involving CO poisoning, it found 58 accidents or incidents. These resulted in 84 fatalities and five serious injuries. In addition, the NTSB looked at the FAA’s database of service difficulty reports filed by mechanics. Between 1974 and 2001, the FAA received 232 reports of cracked or leaking mufflers. Many of the reports noted that the cracks or signs of deterioration couldn’t be detected through a surface visual inspection.

By submitting its safety recommendation, the NTSB wants the FAA to evaluate the methods that are currently used for inspecting mufflers and exhaust systems, and determine whether or not they’re sufficient. Furthermore, the NTSB thinks that the FAA should require replacement of exhaust systems in general-aviation aircraft after a certain time in service and the installation of carbon-monoxide detectors on all single-engine reciprocating-powered airplanes with forward-mounted engines and enclosed cockpits. In addition, the NTSB wants the FAA to establish standards for detectors.

There are several types of CO detectors that are currently available. But whichever type of CO detector you purchase, there’s no denying the fact that bringing one with you in the cockpit is cheap insurance, especially when flying in winter with an enclosed cabin and the heat blasting away.

One of the accidents cited by the NTSB in its safety recommendation involved a Piper PA-28-236. On January 17, 1997, at 1:35 p.m. EST, the single-engine airplane was destroyed when it collided with trees near Alton, N.H. The pilot and one passenger were fatally injured. Visual meteorological conditions prevailed. The personal flight was conducted under Part 91. The flight originated from Farmingdale (FRG), N.Y., at approximately 11:15 a.m. The intended destination was Saranac Lake, N.Y.


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