84-12-01 R1: Approved Rotor Blades

84-12-01 R1 HUGHES HELICOPTERS, INC. (HUGHES HELICOPTERS): Amendment 39-4877 as amended by Amendment 39-4937. Applies to Model 369D and 369E helicopters certificated in all categories. Compliance is required prior to further flight, unless already accomplished. To detect unapproved blades and prevent possible rotor blade failure in flight, accomplish the following: For Hughes Helicopters, Inc., Model 369D and 369E helicopters with main rotor blades installed which have been procured from any source. (a) To verify that the main rotor blades are of the proper Part Number (P/N) 369D21100 internal configuration, comply with the following: (1) A coin tap test or equivalent test shall be used to identify the number of ribs in each blade. Carefully tap along the length of the blade, aft of the spar, from the tip end, using a heavy coin; e.g., U.S. quarter, half dollar, or equivalent. Note the number of ribs in the blade by the difference in sound. The proper P/N 369D21100 blade has 20 ribs, 1.5 inches apart, beginning 1.5 inches from the blade tip. The unapproved 369A1100 series blade has only four ribs, beginning 3 inches from the blade tip. (2) The unapproved blade also has a painted over, flush plug installed to fill a 0.218- to 0.224-inch-diameter hole required in the trailing edge inboard end of all 369A1100 series blades. There is no such hole in the proper P/N 369D21100 blades. Inspect the blade for a filled hole in the trailing edge inboard end. (b) If a blade has four ribs and a filled hole, an improper blade is installed. Replace with an airworthy proper P/N 369D21100 blade prior to further flight. (c) Alternative inspections, modifications, or other actions which provide an equivalent level of safety to this AD may be used when approved by the Manager, Western Aircraft Certification Office, Hawthorne, California. The procedure specified in Hughes Service Information Letter DL-57 or EL-5, dated February 10, 1984, is an alternative. NOTE: Hughes Service Information Letter No. DL-57 or EL-5 dated February 10, 1984, pertains to identification of improper blades. Amendment 39-4877 became effective June 11, 1984. This Amendment 39-4937 becomes effective October 24, 1984.