FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 1. Wood Structure | 3. Inspection | 1-29. Inspection Methods
AC 43.13-1B
9/8/98
and the wood structure). The mechanic should
also look for evidence of swelling or warpage
of the aircraft’s wood structure, which would
indicate underlying damage or decay. Par-
ticular attention should be paid to the wood
structure immediately beneath the upper sur-
faces, especially under areas that are finished
in dark colors, for signs of deteriorating adhe-
sives. Cracks in wood spars are often hidden
under metal fittings or metal rib flanges and
leading edge skins. Any time a reinforcement
plate exists that is not feathered out on its
ends, a stress riser exists at the ends of the
plate. A failure of the primary structure can be
expected to occur at this point.
b. Tapping the wood structure with a
light plastic hammer or screwdriver handle
should produce a sharp solid report. If the
suspect area sounds hollow and soft, further
inspection is warranted by the following meth-
ods.
c. Probe the area in question, if accessi-
ble, with a sharp metal tool. The wood struc-
ture should be solid and firm. If the suspect
area feels soft and mushy the mechanic should
assume that the area is rotted. Disassembly of
the structure is warranted at this point.
d. Prying the area of a bond joint will re-
veal any mechanical separation of the joint. If
the mechanic detects any relative movement
between two adjacent wood members, a failure
of the bond is evident. Any loose fittings
should arouse the mechanic’s suspicion, and
the fittings should be removed to check for
elongated bolt holes. Disassembly is war-
ranted for further inspection.
e. Odor is an important indicator of pos-
sible deterioration. During the initial inspec-
tion, as the access panels are being removed
from the structure, the mechanic should be
aware of any areas that smell musty or moldy.
These odors are indicative of the presence of
moisture and associated fungal growth and
decay.
f. Visual inspection requires looking at
the wood structure both externally and inter-
nally for visual signs of decay or physical
damage. Any accumulations of dirt, bird nests,
or rodent nests are likely places to hold mois-
ture and promote decay.
(1) The mechanic should remove any
such accumulations that are found and inspect
the area for signs of decay. Decay will appear
as a dark discoloration or gray stains running
along the grain and often a swelling of the
wood member if still wet. Fittings will be
imbedded in the wood instead of flush.
(2) Highly suspected structurally dam-
aged areas are shown in figure 1-3. A list of
most likely areas to incur structural damage in-
clude the following:
(a) Check front and rear spars for
compression cracks adjacent to the plywood
reinforcing plates, where the lift struts attach,
and at the rib attach points on either side of the
strut attach points. Triple-check these areas
and the spar to fuselage attach points for
cracks if the wingtip has contacted the ground,
a hangar wall, etc.
(b) Check all metal fittings which
attach to wooden structure for looseness, cor-
rosion, cracks, or warps. Areas of particular
interest are strut attach fittings, spar butt fit-
tings, aileron and flap hinges, jury strut fit-
tings, compression struts, pulley brackets, and
any landing gear fittings.
(c) Check front and rear spars for
longitudinal cracks at the ends of the plywood
reinforcement plates where the lift struts at-
tach. Triple-check this area if the wing has en-
countered any kind of ground strike.
Page 1-12
Par 1-29