COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Enstrom F-28 Series Helicopters AD/ENST 28/21 Tail Rotor Blade Grip - Inspection and Modification 5/79 Applicability: All models F-28C and 280C with Tail Rotor Blade Grip P/N 28-150013-1 wide chord. Document: Enstrom Service Directive Bulletin No. 0048. Compliance: As per requirement document. The Preflight Inspections may be carried out by the pilot in command in which case certification is not required. Background: The manufacturer has received several field reports of crack indications being found in the wide chord tail rotor blade retentions grip.