TM 1-1520-238-23
1-390
Change 10
1.137.
SPECIAL INSPECTION CHECKLIST – continued
Helicopter Serial No.:
Date:
Area
No.
REQUIREMENT
EVERY
Item
Status
Special
Inspection
No.
6
30
50 FLIGHT HOURS
CHECK MAIN ROTOR PITCH HOUSING NUTS FOR THE FOLLOWING:
a. Check torque on 16 nuts using torque wrench set to 270 INCH-POUNDS.
b. Check for proper bolt thread extension through nut. The allowable number
of threads visible beyond the nut is no less than 1 1/2 and no more than
5 1/2.
c. If the torque is 270 INCH-POUNDS or more and the number of visible
threads are within allowable range, the inspection is complete. If either
condition is not met, proceed to step d.
NOTE
Use only one washer under nut on lower pitch housing bolt
(HS1446-6-20) and two washers under nut on upper pitch housing bolts
(HS1446-6-28).
d. If only one bolt on a single pitch housing is less than 270 INCH-POUNDS,
replace nut, bolt, and washer(s) with new ones. Lubricate threads of bolts
and nuts with lubricant (item 114, App F). Torque nut(s) to 350
INCH-POUNDS.
e. If two or more bolts on a single pitch housing are less than 270
INCH-POUNDS, check for possible damage to pitch housing and/or
feather bearing assembly. If no damage is found, replace undertorqued
nuts, bolts, and washers with new ones. Lubricate threads of bolts and
nuts with lubricant (item 114, App F). Torque nuts to 350 INCH-POUNDS.
f. If less than 1 1/2 or more than 5 1/2 threads can be seen beyond the
nut(s), replace nut(s), bolt(s), and washer(s). Lubricate threads of new
bolt(s), nut(s), and washer(s) with lubricant (item 114, App F). Torque nut
to 350 INCH-POUNDS.
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