COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AD/B747/203 Lavatory Drain System Leak Tests 6/99 Applicability: Model 747-100, -200, -300, -SP and -400F series aeroplanes certificated in any category. Requirement: Inspection and maintenance requirements of US FAA AD 99-08-10 are to be performed. Note: FAA AD 99-08-10 amendment 39-11116 refers. Compliance: Initial action and subsequent repetitive actions as defined in US FAA AD 99-08-10 Amdt 39-11116, with a revised effective date of 17 June 1999. This Airworthiness Directive becomes effective on 17 June 1999. Background: Certain design features of the 747 toilet flush system have lead to an increase in the incidences of "blue ice" forming on the airframe and detaching in flight causing damage to the airframe and property on the ground. This directive introduces inspections and maintenance actions to improve the reliability of the system and reduce the possibility of leaks and, ultimately, the likelihood of "blue ice" forming and detaching in flight.