79-11-04: Lower Housing Transmissions

79-11-04 FAIRCHILD (HILLER): Amendment 39-3479. Applies to Model 1100 and FH-1100 type helicopters certificated in all categories. Compliance required as indicated unless already accomplished. In order to prevent cracking of the transmission lower housing gimbal ring support, accomplish the following: a. For P/N 24-23030-7 transmission lower housings (installed in P/N 24-23000-11, -31, and -41 transmission assemblies) which have accumulated 500 or more hours since new or overhauled, inspect and repair as necessary within 50 hours after the effective date of this AD, unless already accomplished within the last 500 hours, in accordance with Fairchild Service Bulletin No. FH-1100-23-10 dated September 25, 1974, revised April 24, 1979. This inspection shall be repeated at each 500-hour interval thereafter. b. For P/N 24-23030-7 transmission lower housings which have accumulated 1200 or more hours, unless already accomplished within the last 1100 hours, ream the gimbalring mounting holes to the next larger size in accordance with Fairchild Service Bulletin No. FH-1100-23-10 dated September 25, 1974, revised April 24, 1979, within 100 hours after the effective date of this AD and at each 1200-hour interval thereafter. c. As a result of the inspection and repair required under paragraphs a and b herein, if the gimbal ring mounting hole diameter exceeds 0.8755 inch or a total time of 3600 hours is attained on the P/N 24-23030-7 lower housing assembly the housing shall be retired from further service. d. Upon installation of transmission lower housing assembly P/N 24-23030-11, the requirements of this AD are no longer applicable. e. Equivalent inspections or parts must be approved by the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region. Upon submission of substantiating data by an owner or operator through an FAA Maintenance Inspector, the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region, may adjust the inspection interval specified in this airworthiness directive. f. Rotorcraft may be flown to a base where the maintenance required by this airworthiness directive is to be performed per FARs 21.197 and 21.199. This amendment is effective June 4, 1979.