Overview

The Civil Aviation Regulations 1998, as amended by the Airworthiness Directive AD/B737/149 issued by the Civil Aviation Safety Authority (CASA) in 2001, address an identified unsafe condition related to the autothrottle systems in Boeing 737-300, -400, and -500 series aeroplanes. This legislative instrument was introduced to rectify irregular autothrottle operations that could lead to asymmetric thrust conditions during flight, potentially causing excessive banking and loss of control. The directive mandates the replacement of existing autothrottle computers with improved models to mitigate these risks, as outlined in Boeing Alert Service Bulletin 737-22A1130 dated 24 September 1998. The policy objective is to enhance flight safety by ensuring that autothrottle computers installed comply with the specified standards, thereby reducing the likelihood of severe flight control issues.

Scope and Application

This Airworthiness Directive issued under the Civil Aviation Regulations 1998 applies to all Boeing 737-300, -400, and -500 series aeroplanes. It mandates that the existing autothrottle computer be replaced with a new, improved version in accordance with Boeing Alert Service Bulletin 737-22A1130 dated 24 September 1998. Additionally, it prohibits the fitting of autothrottle computers with specific Part Numbers to any aeroplane to replace an installed computer. These requirements must be fulfilled within 18 months for the replacement directive and immediately for the prohibition directive, starting from the effective date of the directive, which is 25 January 2001. This Airworthiness Directive was issued due to reports of asymmetric thrust conditions during flight caused by irregular autothrottle operation, and it aims to prevent severe asymmetric thrust conditions that could lead to loss of control of the aeroplane.

Key Provisions

The Airworthiness Directive (AD) under subregulation 39.1(1) of the Civil Aviation Regulations 1998 (CAR 1998) mandates specific actions to be taken for the continued safe operation of certain Boeing 737 series aeroplanes. Specifically, AD/B737/149 pertains to the replacement of the existing autothrottle computer with a new, improved version to mitigate the risk of asymmetric thrust conditions during flight (s. 1(a)-(c)). The applicability of this directive extends to all Model 737-300, -400, and -500 series aeroplanes (s. Applicability). The directive requires that the existing autothrottle computer be replaced with a new one, in accordance with Boeing Alert Service Bulletin 737-22A1130 dated 24 September 1998 (s. Requirement 1). Additionally, specific autothrottle computers with certain part numbers are prohibited from being used in any aeroplane to replace an installed computer (s. Requirement 2). Operators and owners of the affected Boeing 737 series aeroplanes must comply with the AD by replacing the autothrottle computer within 18 months from the effective date of this directive, and immediately prohibiting the use of certain specified part numbers (s. Compliance). The directive further stipulates that compliance must be achieved by following the instructions provided by Boeing and ensuring that the replacement process adheres to the guidelines set forth in the referenced service bulletin. Failure to comply with the requirements set out in this directive could result in continued operation of an aircraft that poses a significant safety risk, potentially leading to loss of control during flight. Non-compliance with this Airworthiness Directive could result in severe penalties. Under CAR 1998, non-compliance may lead to enforcement actions, including fines, grounding of the aircraft, and potential criminal charges for operators found in breach of the directive (s. Offences and Penalties). The maximum penalties for such offences can be substantial, reflecting the seriousness of maintaining aircraft airworthiness and ensuring passenger safety. The directive underscores the importance of adhering to safety regulations to prevent incidents that could endanger lives and property.