46-11-01\tNORTH AMERICAN: (Was Service Note 2 of AD-2-575-3.) Applies Only to Army BC-1A, AT-6, -6A, -6B, -6C; Serial Numbers Below 41-34249 and Navy SNJ-2, -3, -4; Serial Numbers Below 0-43692.\n \n\tInspection required at each periodic inspection unless doubler angles are installed. \n\n\tInspect the inboard end of the landing gear retracting strut attachment support channel, P/N 55-14102 or 66-14102-1, at the wing outer panel joint, for cracks. If cracks are found in any channel, it shall be reinforced as follows: \n\n\tA.\tFor cracks less than 2 inches long, install 0.062 inch-29/32 inch x 1 inch x 6 3/4 inches long, SAE No. 4130 steel, cadmium-plated ( or 0.091 inch-24ST alclad) doubler angles in the upper corners of the inboard ends of each cracked channel. Drill a 1/8-inch stop hole at the end of each crack. Attach the 29/32-inch leg by picking up the existing rivet pattern through the wing skin and the channel upper flange. The rivets through the wing attach angle should be replaced with AN 3 bolts, or equivalent. Attach the 1-inch leg to the side of the channel using a row of seven AN 442-AD4 rivets or equivalent, at approximately 1 1/8-inch spacing. \n\n\tB.\tFor cracks over 2 inches long, install 0.062 inch-29/32 inch x 1 3/8 inches x 6 3/4 inches long SAE No. 4130 steel, cadmium-plated, doubler angles in the upper corners of the inboard ends of each channel containing a crack over 2 inches long. Drill a 1/8-inch stop hole at the end of each crack. Attach 29/32-inch leg as described in paragraph A. Attach 1 3/8-inch leg to the side of the channel using two rows of seven AN 442-AD4 rivets, or equivalent, at approximately 1 3/8-inch spacing. \n\n\tC.\tFor cases where no cracks are found, install the same doubler angles as required in paragraph A, except that they need not exceed 4 inches in length, or inspect at each periodic inspection. \n\n\tIn order to permit installation of rivets with the wing outer panel installed on the airplane, approved type blind 5/32-inch rivets may be used in the 1-inch or the 1 3/8-inch leg of the doubler angle. \n\n\t(Supplement No. 1 to North American Service Bulletin dated March 6, 1946, covers this subject also.)