COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Hiller UH-12 Series Helicopters AD/HILLER 12/33 Tail Rotor Blade P/N 55073 - Inspection 11/81 Applicability: All UH-12 series fitted with tail rotor blades P/N. 55073. Document: Hiller Aviation SB No. 55-1. Compliance: At each daily or overnight inspection. Note: This inspection may be performed and certified for by the pilot in command. Background: There is a possibility of the vent holes located at the inboard and outboard ends of the blade becoming obstructed with dirt or debris.