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 | 1. Engines | 8-9. Self-locking Nuts for Aircraft Engines and Accessories
AC 43.13-1B
9/8/98
if that part either conforms to new part toler-
ances or meets the manufacturer’s service lim-
its. Ensure that used parts are airworthy and
properly identified as a PMA or TSO part.
8-5. OIL SYSTEM LINES INSPECTION.
The inspection of the plumbing for an oil sys-
tem is similar to the inspection of any other
plumbing system. The tubing, hose, tube fit-
tings, hose fittings, hose clamps, and all other
components of the system are inspected for
cracks, holes, dents, bulges, and other signs of
damage that might restrict the oil flow or cause
a leak. All lines are inspected to ensure that
they are properly supported and are not rub-
bing against a structure. Fittings should be
checked for signs of improper installation,
over-torquing, excessive tension, or other con-
ditions which may lead to failure.
8-7. CYLINDER HOLD-DOWN NUTS
AND CAP SCREWS. Great care is required
in tightening cylinder hold-down nuts and cap
screws. They must be tightened to recom-
mended torque limits to prevent improper
stressing and to ensure even loading on the
cylinder flange. The installation of baffles,
brackets, clips, and other extraneous parts un-
der nuts and cap screws is not a good practice
and is discouraged. If these baffles, brackets,
etc., are not properly fabricated or made of
suitable material, they may cause loosening of
the nuts or cap screws even though the nuts or
cap screws were properly tightened and locked
at installation. Improper pre-stressing or loos-
ening of any one of these nuts or cap screws
will introduce the danger of progressive stud
failure with the possible loss of the engine
cylinder in flight.
8-6. OIL FILTER INSPECTION. The oil
filter provides an excellent method for discov-
ering internal engine damage. During the in-
spection of the engine oil filter, the residue on
the screens, disks, or disposable filter cartridge
and the residue in the filter housing are care-
fully examined for metal particles. A new en-
gine or a newly-overhauled engine will often
have a small amount of fine metal particles in
the screen or filter, but this is not considered
abnormal. After the engine has been operated
for a time and the oil has been changed one or
more times, there should not be an appreciable
amount of metal particles in the oil screen. If
an unusual residue of metal particles is found
in the oil screen, the engine must be taken out
of service and disassembled to determine the
source of the particles. As an additional pre-
caution, an oil analysis/trend analysis may pre-
vent an engine failure in flight.
At oil changes, oil samples are often taken and
sent to laboratories to be analyzed for wear by
determining the amount of metal in the sam-
ple. Over time, a trend is developed and the
engine can be removed from service before
failure.
8-8. REUSE OF SAFETYING DEVICES.
Do not use cotter pins and safety wire a second
time. Flat, steel-type wrist pin retainers and
lock washers, likewise, must be replaced at
overhaul unless the manufacturer’s recom-
mendations permit their reuse.
8-9. SELF-LOCKING NUTS FOR AIR-
CRAFT ENGINES AND ACCESSORIES.
Self-locking nuts may be used on aircraft en-
gines provided the following criteria are met:
a. When their use is specified by the en-
gine manufacturer in the assembly drawing,
parts list, and bills of material.
b. When the nuts will not fall inside the
engine should they loosen and come off.
c. When there is at least one full thread
protruding beyond the nut.
d. Where the temperature will not ex-
ceed the maximum limits established for the
self-locking material used in the nut. On many
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