Common Aircraft Exhaust Problems and How to Fix Them
Unlike car exhaust systems, whose only purpose is to reduce noise and take gases away from the engine, aircraft exhaust has more complicated functions such as supplying cabin and carburetor heat.
Because the aircraft exhaust systems (stacks and muffler) are exposed to extreme conditions and temperatures, they require regular exhaust maintenance. The goal is to detect minute cracks and leaks, which can cause further damage and even risk of carbon monoxide poisoning to the occupants if left unchecked.
A word of caution: Owners can perform some of the basic “visual inspections” but should not in any way conduct their own repair nor disassemble/assemble the exhaust system unless they are licensed aircraft mechanics.
Leaks and Cracks on the Muffler
Any bulges or irregularities on the muffler are signs of metal fatigue. Nevertheless, a pristine-looking exterior does not mean that it has no problem whatsoever.
If the plane has straight tailpipes, mechanics can easily check the muffler’s interior with a flashlight and inspection mirror. But for tailpipes with bends, they will need a borescope to examine the internal baffles, which are more prone to wear and tear than the exterior of the muffler because they are more exposed to high temperatures and pressure.
Even if only one of the baffles has a sign of wear and tear, it is a clear indication that the muffler has damage in other areas, which entails a complete overhaul.
Meanwhile, mechanics must also remove all the carbon deposits off the base of the metal for further infection.
Misaligned stacks are one of the most common reasons why cracks on the exhaust systems happen. The usual culprit is a previous shoddy repair or a “patch job.”
Aircraft exhaust systems are made of a special type of stainless steel that makes it extra resistant to corrosion. However, a shoddy repair–i.e., not done in a controlled environment or the mechanic did not use inert gas welding equipment–can ruin the long-term stability of an otherwise repairable exhaust.
In addition, a contaminated weld will eventually crack or leak from repeated vibrations and extreme heat.
A Word of Warning
In many cases, small weld repairs are just a band-aid solution, causing more exhaust system leak in the long run. In this scenario, a better way to address the problem is to replace the entire exhaust component.
As a general rule, any sign of metal fatigue, thinning, and bulges in any part of the exhaust system almost always require a complete overhaul or replacement because wear and tear doesn’t just happen in one isolated spot.
Most seasoned mechanics believe that an isolated repair without overhaul is nothing more than a band-aid solution.
Another thing to keep in mind is to avoid any zinc-plated or galvanized tools and lead pencils when inspecting and repairing the aircraft exhaust system. The stainless steel absorbs the zinc and lead in high temperatures, causing leaks, cracks, and eventual failure.
Common telltale signs of exhaust system leak include yellowish stain or greyish residue around the leaking part. However, not all leaks can be identified by visual inspection alone.
Leaks that are pinholes and pores can’t be seen with the naked eye, so the mechanics need to use a pressure test to blast the muffler with a soapy water solution.
To perform a leak inspection, mechanics insert a vacuum hose into a cold exhaust tailpipe and seal it using duct tape. The hose is then set to “blow” to create pressure in the exhaust system; any leak will be immediately visible as the soap solution bubbles.
When doing a leak inspection, it is important to pay close attention to the welds, clamps, and slip joints where cracks often occur.
Another way to check for leaks is to use a tank of water, although it requires removing the exhaust component from the aircraft.
Frequency of Inspection
Manufacturers specify flight hours rather than timeframes for maintenance and service checks. For small aircrafts, the usual recommendation is after 100 hours of operation and at least an annual comprehensive inspection.