COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Embraer EMB-120 (Brasilia) Series Aeroplanes AD/EMB-120/1 Generator Control Unit (GCU) 2/91 Applicability: Embraer 120 aircraft S/No's 120004; and 120006 through to 120090 inclusive. Requirement: Action in accordance with the technical requirements of Brazilian AD 90-09-03. Note: Embraer SB 120-024-0021 Revision 3 also refers. Compliance: Within 1000 hours time in service after 30 September 1990. Background: Advice has been received that GCU failures may result in momentary overvoltages of sufficient amplitude to cause failure of critical aircraft systems and components.