COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Bell Helicopter Textron 212 Series Helicopters AD/BELL 212/47 Lower Planetary Spider Gear 9/91 DM Applicability: All Models. Requirement: Action in accordance with Bell Alert SB No. 212-91-66. Compliance: As directed in the Requirement Document with a revised effective date 12 July 1991. Background: A special inspection of the main gearbox lower planetary spider gear P/N 204-040- 785-003 has been introduced by the manufacturer after fatigue cracking has been detected.