80-13-12 R1: Longerons

80-13-12 R1 DEHAVILLAND: Amendment 39-3815 as amended by Amendment 39-4135. Applies to all DHC-6 model airplanes, Serial Numbers 1 thru 631, equipped with intermediate or high flotation tires, skis, or floats, certificated in all categories. To prevent possible failure of the engine nacelle lower longerons due to cracking or buckling, accomplish the following: (a) For aircraft equipped with high flotation tires (37 inch diameter or larger) and operating to or from unprepared surfaces, visually inspect inner edge of each engine nacelle lower longeron daily, six to eight inches aft of forward end of longeron, for cracks or buckling. Use at least a ten power glass for crack detection. (b) For aircraft equipped with intermediate flotation tires and operating to or from unprepared surfaces, skis, or floats, visually inspect longerons in accordance with procedure and method in paragraph (a), within 24 hours in service, unless already accomplished within the last 26 hours in service. This inspection must be repeated thereafter term at intervals not to exceed 50 hours in service from the last inspection. (c) For aircraft which have been equipped with any of the above landings or flotation gear and are now equipped with standard wheels and tires, visually inspect longerons in accordance with procedure and method in paragraph (a), within 24 hours in service after the effective date of this AD, unless already accomplished. (d) If cracks or buckles are found, replace the longeron with a serviceable one of the same part number, or with an approved equivalent, before further flight. (e) All above inspections may be discontinued when Modification No. 6/1655, or approved equivalent, is accomplished. (f) Equivalent alterations must be approved by the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region. (g) Compliance times may be increased by the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region, upon receipt of substantiating data submitted through an FAA Maintenance Inspector. Amendment 39-3815 was effective July 1, 1980. This amendment 39-4135 is effective June 19, 1981.