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-2/46 Anti-Ice and De-Ice Systems 5/90 Applicability: Model MU2. Requirement: Carry out an operation check of the airframe and engine anti-ice and de-ice systems in accordance with Chapter 9 of the MU2 Maintenance Manual. Compliance: At each 100 hour maintenance interval. Background: A recent accident investigation revealed that ice accumulation may have been a contributing factor. A surveillance of the M2 fleet revealed an unacceptably high incidence of anti-ice and de-ice systems unserviceability.