COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Beechcraft 90 and 65-90 (King Air) Series Aeroplanes AD/BEECH 90/55 Oxygen System - Inspection 8/80 Applicability: All models with S/Nos. LJ-490 to LJ-667 and LW-1 to LW-326, not modified in accordance with Beechcraft SI No. 0867-341, Rev. 2. Requirement: 1. Fabricate a placard using letters at least 3 mm high to read as follows : "Flight above 25,000 feet prohibited unless oxygen system is ARMED (ON)". 2. Install this placard in clear view of the pilot and operate the aircraft in accordance with this limitation. Compliance: Within the next 50 hours' time in service after 16 July 1980. Background: Overseas experience has shown that this requirement is necessary to prevent seizure and binding of the oxygen control cable due to freezing of contaminating moisture which will interfere with activation of the oxygen system.