AD/LEARJET 35/35 - Mach Limit

Overview

The Civil Aviation Regulations 1998, as amended, include the Airworthiness Directives aimed at ensuring the safety of aircraft in Australian airspace. This particular directive, AD/LEARJET 35/35, targets Gates Learjet 35 and 36 series aeroplanes that have undergone modifications as per FAA Supplemental Type Certificate SA766NW. The directive was introduced to address issues related to aileron buffet or buzz experienced during high-speed cruise, which could lead to a deterioration of the aeroplanes' lateral control characteristics. The objective of the directive is to ensure that such deterioration does not occur, thereby maintaining the airworthiness of these aircraft. This directive became effective on 30 January 1997, and compliance is required within 200 hours of time in service after that date or by 31 July 1997, whichever is earlier. The directive is enforced by the Civil Aviation Safety Authority (CASA), which is the relevant authority for airworthiness standards in Australia.

Scope and Application

The Civil Aviation Regulations 1998, specifically PART 39 - 105, pertains to the Civil Aviation Safety Authority’s Schedule of Airworthiness Directives for Gates Learjet 35 and 36 series aeroplanes, identified as AD/LEARJET 35/35 Mach Limit 2/97. This regulation applies to all Model 35, 35A, 36, and 36A aeroplanes that have undergone modifications in accordance with the United States Federal Aviation Administration (FAA) Supplemental Type Certificate (STC) SA766NW. The primary objective of this directive is to prevent the deterioration of the aeroplanes' lateral control characteristics by mandating specific modifications to ensure safety. This legislation falls under the Commonwealth of Australia and is enforced by the Civil Aviation Safety Authority (CASA). The directive requires compliance within 200 hours of time in service after 30 January 1997 or before 31 July 1997, whichever comes first. The directive became effective on 30 January 1997, addressing reported incidents of aileron buffet or buzz during high-speed cruise, which could lead to unacceptable levels of deterioration in the aeroplanes' lateral system characteristics.

Key Provisions

The Civil Aviation Regulations 1998, specifically Part 39 - 105, sets forth the Civil Aviation Safety Authority (CASA) Schedule of Airworthiness Directives, including AD/LEARJET 35/35, which pertains to the Mach Limit for Gates Learjet 35 and 36 Series Aeroplanes (Section 1). This directive applies to all Model 35, 35A, 36, and 36A aeroplanes that have been modified in accordance with FAA Supplemental Type Certificate (STC) SA766NW. The directive requires operators to either permanently reduce the aeroplanes' maximum operating Mach limit (MMO) by reconfiguring the Mach Overspeed Warning Switch and airspeed indicators, or to remove the modifications installed under FAA STC SA766NW and revert to the original type design configuration or the Gates Learjet "Softflight" configuration. These measures are intended to prevent deterioration of the aeroplanes' lateral control characteristics and address reports of aileron buffet or buzz experienced during high-speed cruise. Compliance with these directives is mandatory within 200 hours time in service after 30 January 1997 or prior to 31 July 1997, whichever occurs first (Section 2). Operators of Gates Learjet 35 and 36 Series Aeroplanes must adhere to the requirements outlined in AD/LEARJET 35/35 to ensure airworthiness. This involves either reducing the MMO by recalibrating the Mach Overspeed Warning Switch and modifying the airspeed indicators, or removing the modifications installed under FAA STC SA766NW and returning the aeroplane to the original type design configuration or the Gates Learjet "Softflight" configuration. To comply with Option 1, operators must remove and re-install the Mach Overspeed Warning Switch, ensuring it is recalibrated and reidentified with the new limit of Mach 0.80. Similarly, the airspeed indicators must be removed, modified, and re-installed, also reidentified with the new Mach limit. Additionally, operators must obtain a Flight Manual Supplement Particular Amendment reducing the Mach limit number from 0.83 to 0.80 from CASA District Airworthiness Offices. Compliance with these actions must be achieved within the specified timeframe to maintain the airworthiness of the aircraft. Failure to comply with the provisions of AD/LEARJET 35/35 could result in serious safety hazards, potentially leading to a deterioration in the aeroplanes' lateral control characteristics, aileron buffet, or buzz. These conditions could compromise the safety of flight operations, and non-compliance may lead to enforcement actions by CASA. While the specific penalties are not detailed in the provided text, non-compliance with airworthiness directives generally could result in civil or criminal penalties, including fines and potential grounding of the aircraft. Operators are therefore required to ensure strict adherence to these directives to avoid any adverse consequences. In summary, AD/LEARJET 35/35 mandates specific actions to maintain the airworthiness of Gates Learjet 35 and 36 Series Aeroplanes. Operators must either reduce the MMO by recalibrating the Mach Overspeed Warning Switch and airspeed indicators, or revert to the original configuration. Compliance is mandatory within a specified timeframe, and failure to adhere to these requirements may result in significant safety risks and potential enforcement actions by CASA.