AD/B737/99 - Main Rudder Power Control Unit (PCU)

Overview

The Civil Aviation Regulations 1998, as amended by the legislative instrument F2006B02999, introduced an Airworthiness Directive specifically targeting the Boeing 737 series aeroplanes. This directive was enacted to address a safety issue identified in the main rudder power control unit (PCU) of the Boeing 737 models. The problem emerged from recent tests conducted by Boeing, which uncovered a potential failure scenario involving the main rudder PCU that could lead to rudder motion opposite to the rudder command if the secondary slide of the PCU jammed in specific positions. The objective of this directive, issued by the Civil Aviation Safety Authority, is to ensure the safety of air travel by mandating regular testing and, if necessary, replacement of the main rudder PCU to prevent such failure scenarios. Compliance with these requirements is critical to maintaining the airworthiness of Boeing 737 aeroplanes. The directive specifies that the test on the main rudder PCU must be conducted in accordance with Boeing Alert Service Bulletin 737-27A-1202 dated 1 November 1996. If the test indicates unusual results, the PCU must be replaced, and the test must be re-conducted. Compliance must be achieved by performing the initial test before 14 November 1996 and subsequently at intervals not exceeding 250 hours of time in service. In cases where the PCU replacement is necessary, it must be completed before further flight. This directive underscores the commitment of the Civil Aviation Safety Authority to proactive safety management in civil aviation.

Scope and Application

The Civil Aviation Regulations 1998, under Part 39 - 105, specifically addresses the airworthiness directives for Boeing 737 Series aeroplanes, with a particular focus on the main rudder power control unit (PCU) as per AD/B737/99. This regulation applies to all models of Boeing 737 aircraft and mandates that operators must conduct a test on the main rudder PCU in accordance with Boeing Alert Service Bulletin (ASB) 737-27A-1202 dated 1 November 1996. This test is crucial to verify the proper operation of the PCU, with the requirement that if the test results in unusual findings as described in the ASB, the main rudder PCU must be replaced, and the test must be re-conducted. Compliance with these requirements involves performing the specified test before 14 November 1996 and subsequently at intervals not exceeding 250 hours of time in service, with the replacement and retesting of the PCU mandated before any further flight if abnormal results are found. This regulation extends across the Commonwealth and is enforced by the Civil Aviation Safety Authority.

Key Provisions

The main operative sections of the Civil Aviation Regulations 1998, Part 39 - 105, Schedule of Airworthiness Directives for Boeing 737 Series Aeroplanes, specifically AD/B737/99, require the performance of a test on the main rudder power control unit (PCU) as per Boeing Alert Service Bulletin (ASB) 737-27A-1202 dated 01 November 1996. This is to verify the proper operation of the PCU. If the test reveals unusual results as described in the ASB, the main rudder PCU must be replaced, and the test must be re-conducted. These requirements are outlined in sections 1 and 2 of the directive. The obligations imposed by this directive are clear and specific. Operators of Boeing 737 models must ensure that the test on the main rudder PCU is performed prior to 14 November 1996 and at intervals not exceeding 250 hours of time in service thereafter. If the test results indicate a need for replacement of the PCU, this must be done before further flight. These obligations are intended to ensure the safety and reliability of the aircraft's rudder system, preventing potential failures that could lead to hazardous flight conditions. The directive also references FAA AD T96-23-51, indicating a cross-jurisdictional recognition of the importance of these safety measures. Failure to comply with the requirements outlined in sections 1 and 2 can have serious implications. The recent tests conducted by Boeing revealed a potential failure scenario where the rudder pedal could cause deformation in the linkage leading to the primary and secondary slides of the servo valve of the main rudder PCU, particularly if the secondary slide jams in certain positions. Such a failure could result in rudder motion in the opposite direction of the rudder command, which poses a significant safety risk. In terms of consequences, while specific penalties are not detailed within the directive, non-compliance with Civil Aviation Regulations can lead to enforcement actions by the Civil Aviation Safety Authority (CASA). This could include fines, suspension or revocation of airworthiness certificates, and potentially criminal charges if the non-compliance results in an incident or accident. The safety of flight is paramount, and adherence to these directives is crucial to maintaining the highest standards of airworthiness.