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
9/8/98
SECTION 3. EXHAUST SYSTEMS
AC 43.13-1B
8-45. GENERAL. Any exhaust system fail-
ure should be regarded as a severe hazard.
Depending upon the location and type of fail-
ure, it can result in carbon monoxide (CO) poi-
soning of crew and passengers, partial or com-
plete engine power loss, or fire. Exhaust sys-
tem failures generally reach a maximum rate of
occurrence at 100 to 200 hours’ operating
time, and over 50 percent of the failures occur
within 400 hours.
8-46. MUFFLER/HEAT EXCHANGER
FAILURES. Approximately one-half of all
exhaust system failures are traced to cracks or
ruptures in the heat exchanger surfaces used
for cabin and carburetor air heat sources.
a. Failures in the heat exchanger’s sur-
face (usually the muffler’s outer wall) allow
exhaust gases to escape directly into the cabin
heat system. The failures are, for the most
part, attributed to thermal and vibration fatigue
cracking in the areas of stress concentration;
e.g., tailpipe and stack, inlet-attachment areas.
(See figures 8-13 through 8-16.)
b. Failures of the spot welds which at-
tach heat transfer pins, as shown in fig-
ure 8-14A, can result in exhaust gas leakage.
In addition to the CO hazard, failure of heat
exchanger surfaces can permit exhaust gases to
be drawn into the engine induction system and
cause engine overheating and power loss.
8-47. MANIFOLD/STACK FAILURES.
Exhaust manifold and stack failures are also
usually fatigue-type failures which occur at
welded or clamped joints; e.g., stack-to-flange,
stack-to-manifold, muffler connections, or
crossover pipe connections. Although these
failures are primarily a fire hazard, they also
present a CO problem. Exhaust gases can
FIGURE 8-13. Typical muffler wall fatigue failure at ex-
haust outlet. (A. Complete muffler assembly with heat
shroud removed; B. Detail view of failure.)
enter the cabin via defective or inadequate
seals at firewall openings, wing strut fittings,
doors, and wing root openings. Mani-
fold/stack failures, which account for ap-
proximately 20 percent of all exhaust system
failures, reach a maximum rate of occurrence
at about 100 hours’ operating time. Over
50 percent of the failures occur within
300 hours.
8-48. INTERNAL MUFFLER FAIL-
URES. Internal failures (baffles, diffusers,
etc.) can cause partial or complete engine
power loss by restricting the flow of the ex-
haust gases. (See figures 8-17 through 8-20.)
Par 8-45
Page 8-23