COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DHC-3 (Otter) Series Aeroplanes AD/DHC-3/35 Electrical System 12/98 Applicability: DHC-3 Otter aircraft that have been modified in accordance with FAA Supplemental Type Certificate (STC) No SA3777NM "Installation of Pratt and Whitney PT6A-135 engine, Hartzell HC-B3TN-3C/T10282 constant speed propeller and other associated changes". Requirement: Modify the auxiliary bus system and replace the voltage regulator together with the voltage-ammeter gauge. The modification and replacements are to be carried out in accordance with A.M. Lutton Electrical Systems Schematic Drawing No 20075 Sheets 1 (Revision G), 2 (Revision E), and 3 (Revision E), all dated 15 May 1998, which are referenced in A.M. Lutton Service Information Letter No SA-SIL-98-11-03 Revision A dated 15 May 1998. Note: FAA AD 98-18-08 Amdt 10724 refers. Compliance: Prior to 5 November 1999. This Airworthiness Directive becomes effective on 5 November 1998. Background: The FAA has determined that the design of electrical system modifications introduced as part of STC SA3777NM was inadequate. This Directive requires modifications to the electrical system which are intended to prevent electrical system failure. Electrical system failure could result in the loss of engine instruments or possible electrical fire in cockpit.