Aircraft Mufflers — The Hidden
Danger You Need to Know
By Jennifer Caron, FAA Safety Briefing Copy Editor
Photo By: Adrian Eichhorn
What if I said that the exhaust system muffler on an airplane is just as critical as the main rotor retaining nut on a helicopter? Would you agree? There is no doubt that if that nut fails, the rotor will lift off the shaft and your next stop is likely the pearly gates. But did you know that if the exhaust muffler is faulty or fails, the consequences can be equally catastrophic? In fact, this is one of the components on an airplane where just a single point of failure could result in fatalities, serious injuries, and/or a total loss of the aircraft. Leaks, metal fatigue, or structural failure in the muffler can cause either a partial or complete engine power loss, a fire, or allow the “silent killer,” carbon monoxide, to find its way into the cabin heating system and poison all aboard.
The FAA is taking a closer look at what appears to be an increasing rate of fatalities and injuries attributed to failures in general aviation (GA) exhaust system mufflers. “We identified 23 accidents/incidents, from 2011 to 2019, where faults or failures in GA exhaust systems were a causal factor,” says Michael Bartron, aerospace engineer in the FAA’s Safety Program Management Branch. “What we’re finding is wear and damage on the inside of the exhaust system. The muffler may be failing in a way that’s not readily visible to a pilot or a mechanic who’s only looking on the outside,” he explains.
Internal muffler failures account for nearly 20% of the total number of exhaust system failures with erosion and carbonizing as the primary cause. If there’s damage starting from the inside out, you have no way of catching it until there’s a rapid failure and then it’s too late.
If you are an owner/operator, removing exhaust system components is not preventive maintenance; however, you should acquaint yourself with the configuration, pieces, and parts that make up the exhaust system on your airplane. This will help you to identify abnormal areas or areas that may have changed since the last inspection. You are primarily responsible for ensuring that defects are repaired between required inspections.
Have your mechanic take the exhaust system off and look inside. Mechanics should remove the heat shroud and inspect the heat exchanger and ducting connections. The FAA recommends that exhaust stacks, mufflers, and tailpipes be replaced rather than repaired, since special tools and welding skills are needed. When exhaust system repairs are necessary, the FAA strongly encourages consultation with an FAA-certificated repair station. “
Yes, it may be time consuming, and owners/operators may not consider it to be the most important system on the aircraft,” says Bartron, “but they need to be fully aware of the life-saving and cost benefits of taking a look on the inside.” Bartron adds that there are simple, non-destructive ways for mechanics to improve their visual evaluations. “You could use a borescope inserted into one end of the removed muffler,” says Bartron.
Inspections, checks, and inspection processes should be accomplished in accordance with the manufacturers’ recommendations. Additionally, FAA Advisory Circular 43.13–1B provides guidance on pressure testing exhaust system components for both installed systems and for removed components.
If you, or other mechanics in your shop, see either brand new issues or “that same old problem” with an exhaust system component, please report it — file a Malfunction/Defect Report (MDR) at av-info.faa.gov/sdrx. You’ll find it under the Public Functions tab. It’s confidential — you can remain anonymous if you choose — and there are no consequences for reporting. “We rely on voluntary feedback from maintenance professionals like you, on the front lines of the industry, to help us collect data, understand trends, and catch problems early,” says Bartron.
💻 To learn more about inspection techniques for GA aircraft exhaust systems, take the AMT Core Course, Aircraft Exhaust Systems (ALC-498) at FAASafety.gov.
Jennifer Caron is FAA Safety Briefing’s copy editor and quality assurance lead. She is a certified technical writer-editor in the FAA’s Flight Standards Service.
Reprinted with permission from FAA Safety Briefing. Visit the Flight Safety Briefing website: https://www.faa.gov/news/safety_briefing/.