COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Gates Learjet 35 and 36 Series Aeroplanes AD/LEARJET 35/35 Mach Limit 2/97 Applicability: All Model 35, 35A, 36 and 36A aeroplanes that have been modified in accordance with United States Federal Aviation Administration (FAA) Supplemental Type Certificate (STC) SA766NW. Requirement: To prevent deterioration of the aeroplanes lateral control characteristics, unless previously accomplished, perform either of the following options: Option 1 - Permanently reduce the aeroplanes maximum operating Mach limit (MMO) by accomplishing the following: 1. Remove the Mach Overspeed Warning Switch and reset it from Mach .83 to .80. Contact the manufacturer, Precision Sensor, PO Box 509, Milford CT 06460 USA (telephone +1 203 877 2795 or facsimile +1 203 877 8752) to have the switch recalibrated. Reidentify the recalibrated Mach Overspeed Warning Switch by ink stamping the words "Mach limit .80' adjacent to the part number. Reinstall the recalibrated switch. 2. Remove the pilot's and copilot's airspeed indicators and have them modified by changing the "barber pole" from Mach number .83 to number .80. The airspeed indicators must be recalibrated by either the manufacture or a facility approved by CASA. Reidentify the modified airspeed indicators by ink stamping "Mach limit .80" adjacent to the part number. Reinstall the modified airspeed indicators. Note 1: A Flight Manual Supplement Particular Amendment reducing the Mach limit number from .83 to .80 is required if Option 1 is followed. This is available from CASA District Airworthiness Offices. Option 2 - Remove the modifications installed in accordance with FAA STC SA766NW and return the aeroplane to either the original type design configuration or to the Gates Learjet "Softflight" configuration. Note 2: FAA AD 85-16-04 Amdt 39-5110 and AD 96-19-13 Amdt 39-9759 refer. Compliance: Within 200 hours time in service after 30 January 1997 or prior to 31 July 1997, whichever occurs first. This Airworthiness Directive becomes effective on 30 January 1997. Background: The FAA has received reports of incidents of aileron buffet or buzz being experienced during high speed cruise. The actions specified by this Directive are intended to prevent aileron buffet or buzz conditions, which could result in deterioration of the aeroplanes lateral system characteristics to an unacceptable level.