COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Sikorsky S-76 Series Helicopters AD/S-76/34 Electrical Power - Essential Bus Modification 10/84 Applicability: All model S-76A Helicopters fitted with Allison 250-C30/250-C30S series engines. Requirement: Modify essential bus installation in accordance with Customer Service Notice CSN 76-149 dated 2 July 1984. Note: FAA Emergency Telegraphic Airworthiness Directive AD No. T84-16-51 refers. Compliance: Within 100 hours time in service from 21 August 1984 but no later than 15 September 1984. Background: Uncontained engine turbine wheel failures have been experienced. This Directive requires modification of the essential bus installation such that turbine wheel failures will not result in the loss of essential electrical services.