COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F28 Series Aeroplanes AD/F28/48 Amdt 1 Horizontal Stabilizer Control Unit Cavity Venting 3/86 Applicability: All models with S/Nos. 11003 to 11211, 11213 to 11218, 11222, 11991 and 11992 fitted with Horizontal Stabilizer Control Units P/No. 11100 - (all dash numbers below - 39AA) S/Nos -001 to -386 disregarding all prefixes. Requirement: Action in accordance with Fokker SB F28/27-161 and subsequent issues, and Menasco SB27-93. Note 1: Fokker SB F28/27-161 draws the attention of operators to the requirements of Menasco SB27-93. Note 2: RLD AD 85-36 refers. Compliance: Before further flight after 30 September 1985. Background: Leakage of a clutch piston seal into the cavity between hydraulic systems 1 and 2 can cause increased seal friction which can lead to a decrease in control unit reliability. To prevent any hydraulic build up within the cavity the existing closed plugs are replaced with vented plugs. This AD has been amended to remove the prefixes from the Stabilizer Control Unit Serial numbers. Federal Register of Legislative Instruments F2006B09782