COMMONWEALTH OF AUSTRALIA CIVIL AVIATION ORDERS CIVIL AVIATION SAFETY AUTHORITY PART 105 SCHEDULE OF AIRWORTHINESS DIRECTIVES GULFSTREAM (GRUMMAN) G.159 SERIES AEROPLANES AD/G159/41 Engine Mount - Inspection and Retirement 2/85 Applicability: All models. Requirement: Inspection: 1. Radiographically inspect the forward and aft engine mount tubes, LH and RH, over their entire lengths. The X-Ray beam may be oriented in any structurally convenient direction except that, in the case of the bottom horizontal tubes of the forward mount, it must be oriented vertically, in order to satisfactorily inspect the lower surface of the tubes. 2. Localised corrosion of the pitting variety is acceptable if the material lost is not more than the equivalent of a 1/4" dia. hole through one tube wall and it is at least one tube diameter away from another corrosion pit. The detection of any pitting corrosion will need to be recorded for life limitation purposes. Compliance paras. 2 and 3 refer. 3. All radiographs which indicate the presence of corrosion which is not clearly less than the limitation of Para. 2 above shall be submitted to the Secretary for assessment. Retirement: 4. Retire from service the Grumman mount assemblies listed in Addendum 6 to Gulfstream I Customer Bulletin No. 241C. Compliance: 1. Unless already accomplshed, inspect before 3600 hours or six years component time in service, whichever is sooner, and thereafter at intervals not exceeding 12 months. Note: Previous inspections in accordance with AD/G159/24B may be considered as having met the inspection requirements of this AD. 2. Retire Grumman mount assemblies in which any corrosion has been detected (even though it may have been subsequently repaired)in accordance with the following: 1. For Grumman mount assemblies with more than 7 500 landings - Within 25 landings after the corrosion is detected, but not later than 30 days, or b. For Grumman mount assemblies with less than 7 500 landings - Before exceeding 7 500 landings. 3. Retire Grumman mount assemblies in which corrosion has not been detected - Before exceeding 20 000 landings. COMMONWEALTH OF AUSTRALIA CIVIL AVIATION ORDERS CIVIL AVIATION SAFETY AUTHORITY PART 105 SCHEDULE OF AIRWORTHINESS DIRECTIVES Background: This directive supersedes and combines the requirements of directives AD/G159/24B and AD/G159/29. Also, as a result of recent fatigue tests conducted by the manufacturer, it permits a life extension to 20 000 landings for Grumman mounts which have no history of corrosion (FAA AD 84-20-08 : Amendment 39-4927 refers). Radiographic inspections are substituted for ultrasonic methods because local experience has proven the former to be more reliable.