COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Lycoming Piston Engines AD/LYC/83 Crankshaft Flange 11/88 Applicability: All AEIO-540-D series, IO-540 (250 & 260 horsepower) engines converted for aerobatic flight or any other 540 engines employing a 2-3/8 diameter main bearing seal used in unlimited category aerobatic manoeuvres. Requirement: Visually inspect the crankshaft flange in accordance with Lycoming Service Bulletin No 482. Compliance: For those engines which have been subjected to unlimited category manoeuvres - initially within 100 hours of engine operation after 3 November 1988 and thereafter at intervals not exceeding each 10 hours of aerobatic flight involving unlimited category manoeuvres. Background: Lycoming SB 482 advises that cracked crankshafts have occurred on applicable engines which have been submitted to unlimited category aerobatic manoeuvres. These manoeuvres are more severe than contemplated when the engines were certificated for prolonged inverted flight and for normal aerobatic manoeuvres. Unlimited category manoeuvres such as multiple snap rolls, inverted flat spins, lomcevaks etc. produce severe bending loads on the propeller flange area. Exceeding engine maximum rated speed and/or using the aircraft in manoeuvres which produce rapid angular propeller centreline acceleration may result in crankshaft failure.