47-20-05
ERCO
(Was Mandatory Note 13 of AD-718-6.)
Applies to 415-C, -CD and -D Aircraft Serial Numbers 800 Through 2037.
Compliance required prior to October 1, 1947.
Cracks have occurred in the belly skin at the rearmost rivet attaching the center section belly skin outer
stiffeners (Erco P/N 415-13056 L/R) to the belly skin.
To prevent similar failures where cracks have not yet developed, install 0.064-inch 24ST alclad angles
1/2-inch wide with legs of 1 3/32 inches and 1/2 inch (Erco P/N 415-13068). Attach the 1 3/32-inch leg to the
outboard side of the aft end of each belly skin outer stiffener with two AN 470AD3-4 rivets (3/32 inch
diameter, universal head, A17ST, 1/4-inch long) and to the center section rear beam with one AN 470AD3-5
rivet. (AN 430 type round head rivets may be used.)
If cracks are found in the belly skin, drill relief holes at the ends of the cracks and install triangular shaped
patch plates as follows in addition to the angle stiffeners described above. Prepare the patch plates of
0.032-inch 24ST alclad material of such a shape that it will pick up the last two rivets which attach the aft end
of the belly skin outer stiffener to the belly skin and the three rivets attaching the rear beam to the belly skin
which are in line with and to either side of the stiffener. Remove the above-mentioned existing rivets and
attach the patch plates through these holes using AN 470AD3-3 and -4 rivets. Attach the patch plate to the
belly skin with six additional AN 470AD3-3 rivets, three through each side of each plate.
(Erco's Ercoupe Service Department Bulletin No. 18 dated January 9, 1947, covers this same subject.)