FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 8. Engines, Fuel, Exhaust, and Propellers | 3. Exhaust Systems | 8-48. Internal Muffler Failures
AC 43.13-1B
9/8/98
FIGURE 8-14. Typical muffler wall failure. (A. Complete muffler assembly with heat shroud removed; B.
Detail view of failure; C. Cross section of failed muffler.)
As opposed to other failures, erosion and car-
bonizing caused by the extreme thermal con-
ditions are the primary causes of internal fail-
ures. Engine after-firing and combustion of
unburned fuel within the exhaust system are
probable contributing factors.
a. In addition, local hot spot areas
caused by uneven exhaust gas flow, result in
burning, bulging, and rupture of the outer muf-
fler wall. (See figure 8-14.) As might be
expected, the time required for these failures to
develop is longer than that for fatigue failures.
Internal muffler failures account for nearly
20 percent of the total number of exhaust sys-
tem failures.
b. The highest rate of internal muffler
failures occurs between 500 and 750 hours of
operating time. Engine power loss and exces-
sive back-pressure caused by exhaust outlet
blockage may be averted by the installation
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