COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Airbus Industrie A319, A320 and A321 Series Aeroplanes AD/A320/18 Trimmable Horizontal Surface Relay 9/91 Applicability: All Airbus Industrie A320 aircraft without Airbus Industrie Modification 21659 or Airbus Industrie Service Bulletin A320-27-1012 embodied. Requirement: Action in accordance with the Technical Requirements of DGAC AD 91-119-017(B) R1. Note: Airbus Industrie Service Bulletin A320-27-1012 also refers. Compliance: 1. For aircraft which have performed more than 1400 flights or more since retrofit of SEC P/N B372ABM0606/B372BAM0404 - at the earliest opportunity, but before exceeding 1600 flights since retrofit of the SEC P/No referenced above. 2. For aircraft which have performed less than 1400 flights or more since retrofit of SEC P/N B372ABM0606/B372BAM0404 - at the earliest opportunity, but within 800, but not exceeding 1600 flights following retrofit of the above referenced SEC. Background: Relay 36 CE 3, which is energised by SEC 2 whenever it is active in pitch mode, has been found, in one case, to be stuck in the energised position. This affects the ability of the SEC 2 monitoring channel to neutralise any erratic movement of the THS initiated by the SEC 2 control channel.