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 | 8-50. Repairs
AC 43.13-1B
9/8/98
of an exhaust outlet guard as shown in fig-
ures 8-21a and 8-21b. The outlet guard may
be fabricated from a 3/16-inch stainless steel
welding rod.
b. Remove or loosen all exhaust shields,
carburetor and cabin heater muffs, shrouds,
heat blankets, etc., required to permit inspec-
tion of the complete system.
Form the rod into two “U” shaped segments,
approximately 3 inches long and weld onto the
exhaust tail pipe as shown in figure 8-21b so
that the guard will extend 2 inches inside the
exhaust muffler outlet port. Installation of an
exhaust outlet guard does not negate the im-
portance of thorough inspection of the internal
parts of the muffler or the necessity of replac-
ing defective mufflers.
8-49. INSPECTION. Inspect exhaust sys-
tems frequently to ascertain complete system
integrity.
CAUTION: Marking of exhaust sys-
tem parts. Never use lead pencils,
carbon based pencils, etc., to mark
exhaust system parts. Carbon depos-
ited by those tools will cause cracks
from heat concentration and carboni-
zation of the metal. If exhaust system
parts must be marked, use chalk,
Prussian blue, India ink, or a grease
pencil that is carbon-free.
a. Before any cleaning operation, re-
move the cowling as required to expose the
complete exhaust system. Examine cowling
and nacelle areas adjacent to exhaust system
components for telltale signs of exhaust gas
soot indicating possible leakage points. Check
to make sure no portion of the exhaust system
is being chafed by cowling, engine control ca-
bles, or other components. The exhaust sys-
tem often operates at red-hot temperatures of
1,000 °F or more; therefore, parts such as ig-
nition leads, hoses, fuel lines, and flexible air
ducts, should be protected from radiation and
convection heating by heat shields or adequate
clearance.
c. Perform necessary cleaning opera-
tions and inspect all external surfaces of the
exhaust system for cracks, dents, and missing
parts. Pay particular attention to welds,
clamps, supports and support attachment lugs,
bracing, slip joints, stack flanges, gaskets,
flexible couplings, and etc. (See figures 8-22
and 8-23.) Examine the heel of each bend, ar-
eas adjacent to welds, any dented areas, and
low spots in the system for thinning and pitting
due to internal erosion by combustion products
or accumulated moisture. An ice pick (or
similar pointed instrument) is useful in probing
suspected areas. Disassemble the system as
necessary to inspect internal baffles or diffus-
ers.
d. Should a component be inaccessible
for a thorough visual inspection or hidden by
non-removable parts, remove the component
and check for possible leaks by plugging its
openings, applying approximately 2 psi inter-
nal pressure, and submerging it in water. Any
leaks will cause bubbles that can be readily
detected. Dry thoroughly before reinstallation.
8-50. REPAIRS. It is generally recom-
mended that exhaust stacks, mufflers, tail-
pipes, and etc., be replaced with new or recon-
ditioned components rather than repaired.
Welded repairs to exhaust systems are compli-
cated by the difficulty of accurately identifying
the base metal so that the proper repair materi-
als can be selected. Changes in composition
and grain structure of the original base metal
further complicates the repair. However, when
welded repairs are necessary, follow the gen-
eral procedures outlined in Chapter 4; Metal
Structure, Welding, and Brazing; of this AC.
Retain the original contours and make sure that
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