COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DH114 (Heron) Series Aeroplanes AD/DH114/6 Amdt 2 Applicability: All models. Mainplane Upper and Lower NK Spar Booms - Inspection Requirement: 1. Inspect the wing main spar upper and lower booms from outboard of the main fuel tank bays to the tip (i.e. from ribs 04 to 22 rear, and from ribs 03A to 22 front), in accordance with De Havilland and TNS No. W7, Issue 2. 2. Inspect the wing main spar upper and lower booms in the area of the main fuel tank bays (i.e. from ribs 01 to 04 rear and from ribs 01 to 03A front) in accordance with De Havilland TNS No. W7, Issue 2. Compliance: For para. 1: (a) Aircraft not modified in accordance with Heron Mod. No. 790 or No. 779 - at intervals not exceeding 6 months. (b) Aircraft modified in accordance with Heron Mod. No. 790 or No. 779 - at intervals not exceeding 12 months. For para. 2: (a) If corrosion is found to be present on the upper or lower spar booms during inspection in accordance with para. 1 of this Directive - before further flight. (b) Otherwise at intervals not exceeding those specified in De Havilland Heron Recommended Maintenance Schedule for removal of the fuel tanks.