AD/B747/317 - Inadvertent Commanded Shutdown of the Engine Bleed Air Systems

Overview

The Civil Aviation Safety Authority (CASA) issued Airworthiness Directive (AD) B747/317 under subregulation 39.1(1) of the Civil Aviation Safety Regulations 1998 (CASR 1998) to address the issue of inadvertent commanded shutdowns of engine bleed air systems in Boeing Model 747-400, -400D, and -400F series aircraft. This AD was issued on 11 November 2004, and became effective on 23 December 2004. The directive was introduced in response to a safety concern identified by Boeing regarding an engine configuration wiring fault that could erroneously identify the engine type fitted to the aircraft, potentially causing an inadvertent shutdown of the engine bleed air distribution systems. Such a shutdown may lead to depressurisation of the aircraft, ice build-up on engine inlets during descent, ingestion of ice into the engine(s), and loss of thrust on one or more engines. The AD requires specific modifications and functional tests to be performed on the aircraft's wiring and air supply control test unit to prevent such occurrences and ensure compliance with the safety standards set out in the directive.

Scope and Application

The Airworthiness Directive issued by the Civil Aviation Safety Authority (CASA) pertains to specific Boeing 747-400, -400D and -400F series aircraft, as identified in Boeing Service Bulletin 747-36A2136 Revision 2. This legislation applies to the aforementioned aircraft models to rectify an unsafe condition that may lead to inadvertent commanded shutdown of the engine bleed air systems, potentially resulting in depressurisation of the aircraft and ice build-up on the engine inlets during descent. The directive is aimed at ensuring that modifications and tests of the wiring of the wire integration unit and air supply control test unit of the engine bleed air distribution system are performed as per the specified instructions. The AD applies nationally within the Commonwealth of Australia, and it is effective from 23 December 2004. The modifications and tests must be completed within 18 months from the effective date of the AD, and post-installation tests must be conducted before further flight. Additionally, specific parts identified in the Hamilton Sundstrand Service Bulletin must not be installed on any aircraft. The AD extends its application through subordinate instruments as specified in Boeing Service Bulletin 747-36A2136, Revision 2.

Key Provisions

This Airworthiness Directive (AD) issued under the Civil Aviation Safety Regulations 1998 (CASR) mandates specific actions for certain Boeing 747 series aeroplanes to address an unsafe condition related to the engine bleed air systems. The AD applies to Boeing Model 747-400, -400D, and -400F series aircraft as listed in Boeing Service Bulletin 747-36A2136, Revision 2, dated 13 May 2004. The directive requires that specified modifications and tests be performed on the wiring of the engine bleed air distribution system, specifically the wire integration unit (WIU) and the air supply control test unit (ASCTU). This includes removing the existing ASCTU, making wiring changes, conducting resistance tests, and installing a new or reworked ASCTU. Post-installation tests must also be conducted in accordance with Boeing Service Bulletin 747-36A2136, Revision 2. Modifications and tests performed before the effective date of the AD are acceptable if the resistance tests were conducted with the ASCTU removed. If resistance tests were conducted with the ASCTU installed, the ASCTU must be removed, the resistance tests performed, and the ASCTU reinstalled, followed by post-installation tests. Additionally, an ASCTU with a part number listed in the "Old Part Number" column in the table specified in Hamilton Sundstrand Service Bulletin 36-186, dated 30 March 2001, must not be installed on any aircraft. The AD imposes several obligations on the parties it governs. Primarily, it mandates that the specified modifications and tests be carried out within a specified timeframe. Requirement 1 must be completed within 18 months from the effective date of the AD, while Requirement 2 must be completed before further flight following the completion of Requirement 1. Requirement 3 also must be completed within 18 months from the effective date of the AD, and Requirement 4 must be completed before further flight following the completion of Requirement 3. Requirement 5, which prohibits the installation of certain ASCTUs, must be adhered to from the effective date of the AD. These obligations are intended to ensure that the specified modifications and tests are performed in a timely and safe manner to mitigate the risk of inadvertent engine bleed air system shutdowns. Failure to comply with the AD may result in civil and criminal consequences. Under CASR 39.03, non-compliance with an AD is an offence and may result in enforcement action, including fines and imprisonment. The maximum penalty for contravening this AD could include a substantial fine and/or imprisonment, as outlined in the relevant sections of the Civil Aviation Act 1988 and CASR. Additionally, failure to comply with the AD may lead to the grounding of the affected aircraft until the required modifications and tests are completed, thereby impacting the operator's ability to fly the aircraft commercially. These consequences underscore the importance of adhering to the AD to ensure the continued airworthiness of the affected aircraft.