COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Cessna 400 Series Aeroplanes AD/CESSNA 400/37 Crankcase Oil Separator Return Line Check Valve - Incorporation of 8/73 Applicability: Model 421B S/Nos. 421B0260 to 421B0346 fitted with new Airesearch TH0871 turbochargers with S/No. prefixes BC or later. S/Nos. 421B0001 to 421B0259 fitted with new Airesearch TH0871 turbochargers with S/No. prefixes BC or later or with remanufactured Airesearch TH0871 turbo-chargers with S/No. prefixes BCR or later. Document: 1. Cessna SL ME73-10; or 2. FAA AD 73-13-8. Effective: 28 September 1973.