COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Propellers - Variable Pitch - Hoffman AD/PHOF/1 Blade Pitch Change Fork - Replacement 5/83 Applicability: All Hoffman variable pitch Model HO-V123 series propellers fitted to Lycoming Model 0-540 and IO-540 series engines. Requirement: Required action: (a) The forks and the pitch change blocks are to be exchanged in accordance with instructions given in overhaul manual E 105 by an appropriately approved organisation. Part Old P/No. New P/No. Pitch change fork VP 20-747 VP 20-909 Pitch change block, symetric alternatively VP 20-554 VP 20-912 Pitch change block, unsymmetrical VP-20-550 VP 20-908 (b) Mark modified propellers with 4 mm high letters "SB 3" above the manufacturing year. Note: German A.D. Luftfahrt-Bundesamt 63-303-61-83-29 refers. Compliance: Part 1: All models fitted to aerobatic certificated aircraft, by 31st July, 1983. Part 2: All other models by the next reconditioning inspection or 30th November, 1983 whichever is the sooner. Background: The manufacturer advises that reports have been received of cracked pitch change forks particularly on aerobatic certificated aircraft, consequently a stronger designed pitch change fork has been introduced.