As winter approaches here in the Northern Hemisphere, it’s time to prepare for operating aircraft in colder temperatures. For many single-engine aircraft powered by reciprocating engines, winter flying means heating the aircraft cabin by way of the exhaust system and a heat exchanger. The warm cabin air is a direct result of fresh air passing over and around the aircraft muffler or heat exchanger.
The importance of maintaining the condition of the exhaust system and associated components can not be overstated. A poorly maintained system can cause dangerous exhaust fumes to make their way into the cabin and ultimately can cause carbon monoxide poisoning to the unsuspecting pilot and passengers. Over the years there have been numerous articles, technical bulletins, and Airworthiness Directives relating to exhaust systems.
In 2009 the Federal Aviation Administration tasked Wichita State University to conduct research that focused on carbon monoxide safety issues as they apply to general aviation aircraft. The full report titled “Detection and Prevention of Carbon Monoxide Exposure in General Aviation Aircraft, Document No. DOT/FAA/AR-09/49, dated October 2009” can be found at the National Technical Information Services web site at http://www.tc.faa.gov/its/worldpac/techrpt/ar0949.pdf.
FAA Special Airworthiness Information Bulletin
As a result of this study and report, the FAA released another Special Airworthiness Information Bulletin (SAIB) CE-10-33, dated May 7, 2010, and a subsequent revision CE-10-33R1, dated Aug. 16, 2010, to communicate an airworthiness concern with exhaust system heat exchangers that are used for heating the aircraft cabin.
The following excerpt comes directly from the SAIB:
The report shows that after researching National Transportation Safety Board (NTSB) accidents related to carbon monoxide (CO) poisoning, the muffler system was the top source of CO. For the CO-related cases where the muffler was identified as the source of the CO leakage, 92 percent had a muffler with more than 1,000 hours of service.
The SAIB goes on to recommend the following four items:
- Replace the mufflers on reciprocating engine-powered airplanes that use an exhaust system heat exchanger for cabin heat with more than 1,000 hours on the muffler and at each 1,000-hour interval, unless the manufacturer recommends or FAA regulations require a more frequent replacement.
- Review and continue to follow the guidance for exhaust system inspections and maintenance in SAIB CE-04-22, dated Dec. 17, 2003, and Advisory Circular 43-16A, Aviation Maintenance Alert (AMA), issued October 2006, All Powered Models, Carbon Monoxide Poisoning Potential.
- Use CO detectors while operating your aircraft as recommended by SAIB CE-10-19R1, dated March 17, 2010.
- Continue to inspect the complete engine exhaust system during 100-hour/annual inspections and at inspection intervals recommended by the aircraft and engine manufacturers following their applicable maintenance manual instructions.
AMT talks to the experts
To understand more on exhaust system inspection and maintenance best practices, AMT visited Aerospace Welding Minneapolis Inc. (AWI), an FAA-approved repair station specializing in repair and overhaul of general aviation aircraft exhaust systems. Tom Heid, the company’s president, shares, “Over the years there has been progressive information supporting the importance of this subject. The concern is that the importance of the issue is not going away.”
Heid went on to explain how normal wear and tear damage to a muffler occurs on inside, and as a result, the inside of an exhaust component is always in worse condition than the outside. This is due to the chemical reactions taking place in the metal when it is continually exposed to exhaust gases and heat. Visually inspecting the outside of a muffler may not be good enough. The importance of thoroughly inspecting the inside of a muffler can not be overstated.
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