TM 1-1520-238-23
15-6
Change 5
15.1.
AUXILIARY POWER SYSTEM COMPONENTS INSPECTION - continued
(1) Thinning below 0.016 INCH is not allowed.
o. Check APU combustor cap flange for deformation. Deformation greater than 0.125 INCH not allowed.
p. Check fuel nozzle for cracks. None allowed.
q. Check igniter plug ceramic insulation for cracks and chips. None allowed.
r. Check igniter plug electrode for damage.
(1) Protrusion less than 0.010 INCH above ceramic insulation not allowed.
s. Check ignition lead for burned spots, cracked or chafed insulation, and any other damage. None
allowed.
t. Check APU exhaust nozzle and duct for leaks, cracks, dents, and distortion. Use depth gage.
(1) Dents and distortion shall not exceed 0.125 INCH.
u. Check APU exhaust nozzle and duct for oxidation erosion and pitting. Use depth gage. Oxidation erosion
and pitting shall not exceed 0.050 INCH.
v. Inspect exhaust duct insulation for cracks, tears, holes, or punctures. If cracks, tears, holes, or punctures
are found and are less than four inches, repair (para 15.40).
w. Check exhaust duct for gaps in weld areas located between duct and insulation. If gaps in weld are
found, insulation may be rolled back four inches or less, repair (para 15.40).
x. Check exhaust duct for dents that exceed 0.500 INCH in depth. None allowed.
y. Check APU support strut and truss assemblies for cracks, dents, scratches, distortion, loose bolts,
and elongated holes.
(1) Fluorescent-penetrant inspect if cracks are suspected (TM 55-1500-335-23). Replace if cracks are found.
(2) Scratches 0.010 INCH maximum must be blended out. Replace if scratches are deeper than 0.010 INCH.
(3) Dents shall not exceed 0.010 INCH and must be blended out. Replace if dents are deeper than 0.010
INCH.
(4) Check the entire length of each weld line for cracks and any other abnormalities. Use inspection mirror as
required.
z. Check APU support strut and truss assemblies for corrosion (para 1.49).
aa. Check APU support strut and truss assemblies attachment points for loose or missing hardware. All
bushings must be in place and hardware must be securely torqued (para 15.31/para 15.32/para 15.33).
ab. Check length of aft support strut (para 15.31).
ac. Check the APU deck fittings for detectable motion, cracks, elongated holes, and missing hardware
(para 15.34/para 15.35). None allowed.
ad. Secure removed panels as necessary (para 2.2).
END OF TASK
