COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Oxygen Systems AD/OXY/3 Amdt 1 Puritan-Bennett Oxygen Regulator NK Diaphragm - Replacement Applicability: Puritan-Bennett Aero Systems Company oxygen masks as follows : P/N 174039 S/N 0001-0012, P/N 174010-01 and 174010-03 S/N 00100-00144, 00146, 00147, 00149-00259, 00261-00273, 00275-00292, 00294-00390 and P/N ZMR 100 series S/N 6603-7234. Requirement: 1. Remove diaphragm assembly P/N F334-1001-1 and install diaphragm assembly P/N F334-1001-1 modified to include diaphragm and plate assembly P/N F334- 1003-1 Revision E. 2. After modification per para. 1, permanently mark letter "M" at the end of or beneath the mask serial number. This serial number is located under the face cushion on the left-hand side of the hardshell on the 174039 and ZMR 100 series masks, and on the back surface of the head harness on the 174010-01 and 174010- 03 masks. 3. The modified diaphragm replacement (para. 1) shall be accomplished by returning the mask to Puritan-Bennett Aero Systems Company, 111 Penn Street, El Segundo, California 90245, USA. However this replacement in ZMR 100 series masks listed below may be accomplished in the field in accordance with the following Puritan-Bennett Aero Systems ATA Component Maintenance Manuals: 35-10-25 for the ZMR 160 mask. 35-10-27 for the ZMR 129 mask. 35-10-28 for the ZMR 129-1 mask. 35-10-29 for the ZMR 118 mask. Note 1. Puritan-Bennett Aero Systems Company Service Bulletin No. 1 pertains to this subject. Note 2. FAA AD 81-08-04 Amendment 39-4092 refers. Compliance: Within 100 hours time in service after 30 June 1981. Note: Oxygen masks which have previously been reworked in accordance with AD/OXY/3 are deemed to comply with this Directive AD/OXY/3A. Background: The regulators in approximately half of the mask assemblies listed contain oversize diaphragms. Under certain conditions, an oversize diaphragm can cause a regulator inlet valve either to leak or to develop positive pressure within the face cone. Although the regulator may work properly in normal usage, it can develop one of the above conditions without warning. There is no reliable field test method for determining when or whether the mask will develop a problem. This Directive is revised in issue to conform with revisions to FAA AD 81-02-03 which include additional S/Nos. of masks and a method of field compliance.