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 28/32 Amdt 1 Tail Rotor Gearbox 3/90 DM Applicability: All model F28, F28A, F28C, F28C-2, F28F, 280, 280C, 280F and 280FX with tail rotor gearbox P/N 28-13500-1, 28-13525-1, -3 or -5 installed and containing spiral miter gear-set "Boston Gear XR-137-2YR or XR-137-2YL". Requirement: Inspect in accordance with Enstrom Service Directive Bulletin 0078. Note: FAA AD 90-01-06 Amdt 39-6457 refers. Compliance: Unless already accomplished, within 10 hours time in service after 9 February 1990 or by 28 February 1990, whichever occurs first. Thereafter, reinspect ALL tail rotor gearboxes in accordance with the requirement document at intervals not exceeding 100 hours time in service. Background: The manufacturer has received two reported cases of chipped or broken teeth in the tail rotor gearbox, and one case of total gear failure. This AD requires a precautionary inspection of the gearbox oil for particulate metal contamination. Although not called up in the Requirement document this Amendment extends compliance to the F-28 model and gearbox P/N 28-13500-1 in line with the now referenced FAA AD.