COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES British Aerospace BAe 3100 (Jetstream) Series Aeroplanes AD/JETSTREAM/57 Tail Unit De-Icing System 1/93 Applicability: All Model 3100, and All Model 3200 up to and including constructors number 969 and constructors number 971. Requirement: Action in accordance with BAe Jetstream Mandatory ASB 30-A-JA 920444. Compliance: Part 1: Within 150 hours time in service after 7 January 1993, and thereafter at intervals not to exceed 150 hours time in service until Part 2 or 3, as applicable, is accomplished. Part 2 or 3: Prior to 30 April 1993. Background: The manufacturer has determined that the possibility exists for water to become entrapped in the tail unit de-icing system. If sufficient water has collected, ice can form in cold conditions which could restrict or prevent the air flow, causing unsatisfactory operation of the tailplane de-icing boots.