COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F28 Series Aeroplanes AD/F28/73 Amdt 1 Passenger Door Lock Warning System 10/93 Applicability: All Model F28 (except Mk 0100), all serial numbers which have Service Bulletin F28/52-72 incorporated. Requirement: Action in accordance with Fokker SB F28/52-101 dated 1 November 1988 or Revision 1 dated 24 August 1992. Note: RLD AD 92-117/2 (A) dated 12 July 1993 refers. Compliance: The original compliance was prior to 4 September 1993. The compliance for this issue is prior to 1 November 1993. Background: For some time, incidents have been reported of passenger doors opening shortly after take-off. In each case, an improperly locked door was left unobserved by cabin crews, while flight crews probably overlooked the DOOR UNLOCKED warning light during their pre-flight checks. In 1988 Fokker issued service Bulletin F28/52-101 to improve the passengers door lock warning system. All the incidents occurred on aircraft on which this particular improvement had not been incorporated. Although the existing door lock warning system should be adequate, a recent incident, in which a door opened at 21,000 feet, prompted another review of the system. Fokker considers that all occurrences could have been avoided if this modification had been accomplished. The RLD and CAA concur with this view and since the unsafe condition described may exist or develop on other aircraft of the same type design, this Airworthiness Directive requires the modification of the passenger door lock warning system. This amendment is issued following the amendment of the RLD Airworthiness Directive and changes the applicability to aircraft in a post SB F28/52-72 configuration.