COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Piaggio P166 Series Aeroplanes AD/P166/10 Undercarriage Warning Horn Circuit - Modification NK Applicability: S/Nos. prior to 409. Requirement: Connect the undercarriage warning horn switches in parallel. Compliance: Forthwith.