AD/B767/47 - Hydraulic Power Transfer Unit System

Overview

The Civil Aviation Regulations 1998, enacted by the Parliament of Australia, address various aspects of civil aviation safety, including the issuance of airworthiness directives to ensure aircraft meet safety standards. One such directive is AD/B767/47, which was introduced to address a safety concern identified in Boeing 767 series aeroplanes. The problem it was introduced to address was the potential marginal pitch control during approach and landing if both left and centre hydraulic systems became inoperative, particularly under adverse centre-of-gravity and gross weight combinations. The policy objective of this directive is to mandate modifications to the hydraulic power transfer unit system to provide stabiliser pitch control and additional landing flare capacity, thus enhancing flight safety. Compliance with this directive was required before 9 April 1992.

Scope and Application

The Civil Aviation Regulations 1998, as amended, under the legislative instrument F2006B03401, apply specifically to the maintenance and operation of Boeing 767 series aeroplanes, namely the B767-200 and B767-300 models. This regulation targets aircraft that have not incorporated the Production Revision Record (PRR) B-11777 and mandates modifications to the hydraulic power transfer unit system in accordance with specified Boeing Alert Service Bulletins. The geographical reach of these regulations is national, as they are administered by the Commonwealth of Australia under the Civil Aviation Safety Authority (CASA). The regulation is precise in its application to certain aeroplanes identified in Boeing Alert Service Bulletin 767-29A0039, dated 11 May 1989, and its subsequent revision, 767-29A0039, Revision 1, dated 2 November 1989, ensuring compliance before 9 April 1992. These directives are aimed at enhancing safety by ensuring adequate pitch control and landing flare capacity in the event of simultaneous hydraulic system failures, thus addressing potential hazards associated with adverse centre-of-gravity and gross weight combinations. The regulation also references the Federal Aviation Administration's AD 90-18-04 Amendment 39-6714, indicating alignment with international safety standards.

Key Provisions

The Civil Aviation Regulations 1998, specifically Part 39 - 105, detail the Civil Aviation Safety Authority's (CASA) schedule of airworthiness directives for various aircraft, including Boeing 767 series aeroplanes. The relevant directive, AD/B767/47, pertains to the hydraulic power transfer unit system. The directive applies to all model B767-200 and B767-300 series aeroplanes that have not incorporated Production Revision Record (PRR) B-11777 (section 1). The directive mandates modifications to these aircraft as outlined in Boeing Alert Service Bulletin 767-29A0039, dated 11 May 1989, for those identified in the bulletin, and Boeing Alert Service Bulletin 767-29A0039, Revision 1, dated 2 November 1989, for all others (section 2). Compliance with these modifications is required before 9 April 1992. The obligations imposed by this directive require the modification of the specified Boeing 767 series aeroplanes to address a critical safety issue identified by Boeing. Specifically, the modifications aim to mitigate the risk of inadequate pitch control during approach and landing if both the left and centre hydraulic systems become inoperative under certain conditions. The addition of the power transfer unit system will provide necessary stabiliser pitch control and enhance landing flare capacity, ensuring safer operations under adverse conditions (section 3). Operators and owners of the affected aircraft must ensure that the required modifications are completed before the stipulated deadline to maintain compliance with airworthiness standards. Failure to comply with the requirements of this airworthiness directive may result in serious consequences. Non-compliance could lead to the aeroplanes being deemed non-airworthy, which could result in grounding or other regulatory actions by CASA. Additionally, the potential for accidents or incidents due to inadequate pitch control during critical flight phases could lead to severe safety risks. Boeing's analysis suggests that without the mandated modifications, the margin for error during landing could be dangerously narrow, leading to potentially catastrophic outcomes (section 4). Therefore, adherence to the directive is not only a regulatory requirement but also a critical safety measure.