75-03-04: Tail Fin Spar

75-03-04 FAIRCHILD (HILLER): Amendment 39-2071 as amended by Amendment 39-2251. Applies to model 1100 and FH1100 type helicopters certificated in all categories. To detect cracks in the tail fin spar channel, P/N 24-62030-7 or P/N 24-62030-43 in the area of the tail rotor gear box mount, P/N 24-62006-3, accomplish the following inspection or an equivalent inspection approved by the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region, within the next five hours in service after the effective date of this AD unless already accomplished within the last 95 hours in service and at every 100 hours in service thereafter: 1. Remove tail rotor gear box fairing and fin leading edge cover. 2. Clean the tail fin spar in an area one inch in diameter around the left and right forward attachment bolts (two of ten to which the tail rotor gear box mount is attached to the spar) and the spar surface between these two attachments and forward, for a distance of 1 1/2 inches with metachlor or equivalent grease and oil remover by light scrubbing with a stiff bristle brush. 3. Inspect the cleaned area for cracks with at least a ten power magnifying glass by looking through the front end of the tail rotor gear box mount fitting. 4. If a crack is found, replace with an uncracked fin assembly that has been inspected in accordance with the above procedure or alter fin in accordance with an alteration approved by the Chief, Engineering and Manufacturing Branch, Eastern Region before further flight. Amendment 39-2071 was effective January 27, 1975, and was effective for all recipients of the airmail letter of December 9, 1974, upon receipt. This amendment 39-2251 is effective July 8, 1975.