COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Mitsubishi MU-2 Series Aeroplanes AD/MU-2/49 Amdt 1 Applicability: All Models. Underwing Pressure Bulkhead Flange 10/94 Requirement: Remove the necessary internal cabin lining and perform a close visual inspection of the underwing pressure bulkhead. Look for cracks in the bend radius of the flange on both left and right hand sides of the bulkhead from F.Sta.3905 to F.Sta.4660. Compliance: Prior to exceeding 5000 pressurised flights or prior to 11 October 1991, whichever occurs later. Thereafter at intervals not to exceed 1000 pressurised flights, and at any time there is an unexplained difficulty maintaining cabin pressure. The compliance of the initial issue of this Directive remains unchanged. This amendment is effective from 15 September 1994. Background: There had been a report of a 300mm long crack in the bend radius of the pressure bulkhead flange on an Australian registered aircraft. Undetected cracking could cause a sudden loss of cabin pressure in flight. Amendment 1 is issued to specify the exact location of the area to be inspected in response to a reported misunderstanding in the field.