Thrush Aircraft S2R-R1340 Maintenance Manual page 226

o Discard all of the old nuts, bolts and washers.
o Clean the lower spar cap inboard ends and the splice block halves, removing any
corrosion.
o Visually inspect the interior surfaces of the bolt holes of the upper and lower splice
block halves. Any scratches must be polished out and the hole inspected the
same as the lower spar cap.
Experience has shown that fatigue cracks may occur in or around the first two (5/16") holes
of the lower spar cap, on the forward or aft side. Thus the top and bottom surfaces of the
lower spar caps must be inspected around the first two holes, and the interior surfaces of the
holes themselves must be inspected. If magnetic particle inspection is to be used, the paint
within ¾" of the two 5/16" holes will need to be removed from the top and bottom of the lower
spar cap.
The inspection must be accomplished by an FAA approved repair station (or foreign
equivalent) with NDT certification. The inspection itself must be performed or supervised by
a level 2 or level 3 inspector per MIL-STD-410E, ISO 9712, or SNT-TC-1A.
If Magnetic particle inspection is used, ASTM E1444-01 must be followed, using wet particles
meeting ASTM 3046.
If using eddy current methods for the inspection, contract with a shop that already has an
approved procedure for inspecting to AD 2006-07-15, if possible. Otherwise a procedure
must be sent to the FAA, Atlanta Aircraft Certification Office (ACO) for approval before doing
the inspection. Send your proposed procedure to:
FAA Atlanta Certification Office, ACE-115A
One Crown Center
1895 Phoenix Blvd., Suite 450
Atlanta, GA 30349
Attn: Ms. Cindy Lorenzen
If the inspection detects a crack in either of the holes or emanating from either of them,
ground the airplane immediately. You may, at your option, elect to inspect using a different
method to confirm the presence of a crack.
If a crack is confirmed, that lower spar cap must be replaced. It is highly recommended that
both wings have their lower spar caps replaced at the same time. If one spar cap is fatigued,
so is the other one, and a crack will show up shortly. Replacing them both will avoid the
extra down time.
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THRUSH AIRCRAFT, INC – MODEL S2R-R1340
AIRCRAFT MAINTENANCE MANUAL
THE INSPECTION
REASSEMBLY INSTRUCTIONS
Effective: 1/1/08