AD/B747/41 Amdt 1 - Fuselage Section 41, Stringer 6 - Stations 340 to 400

Overview

The Civil Aviation Regulations 1998 were enacted in 1998 to ensure the safety of civil aviation in Australia. They form the primary regulatory framework governing all aspects of civil aviation in the country, including aircraft operations, maintenance, and airworthiness standards. The regulations were introduced to address the need for a comprehensive, cohesive, and enforceable legal framework to ensure the safety and efficiency of civil aviation within Australia. They are administered by the Civil Aviation Safety Authority (CASA) on behalf of the Australian Government and are intended to ensure the highest standards of safety and efficiency in the operation of civil aircraft. A specific part of these regulations is the Schedule of Airworthiness Directives, which includes AD/B747/41 Amdt 1. This particular Airworthiness Directive pertains to the Boeing 747 series aeroplanes and was introduced to address the problem of pressure cycle fatigue leading to skin cracks in the fuselage section 41, stringer 6 area between body stations 340 to 400. The policy objective of this Airworthiness Directive is to ensure the continued airworthiness of Boeing 747 series aeroplanes by requiring inspections and, where necessary, modifications to prevent in-flight cabin depressurisation and ensure the aircraft can withstand required loads. This is achieved through the implementation of detailed visual and eddy current inspections, as well as modifications to the affected areas, in accordance with the specified Boeing Service Bulletins.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 105 Civil Aviation Safety Authority Schedule of Airworthiness Directives, applies to Boeing 747 series aeroplanes, targeting the inspection and modification of specific structural components. The directive mandates close visual and eddy current inspections of the stringer S-6L and S-6R fuselage skin lap joints for cracks, and requires modifications to these components to address fatigue-related skin cracks, a critical safety concern identified in this aircraft model. The inspection and modification requirements vary based on the aircraft’s flight history, with distinct intervals prescribed for aircraft with less than 10,000 flights and those with more. Areas that have undergone modification are subject to different inspection intervals, and the directive is designed to ensure that these crucial structural elements remain intact, preventing potential in-flight depressurisation and structural failure. This legislation has a national jurisdictional reach, enforced by the Civil Aviation Safety Authority within Australia, and extends its applicability through subordinate instruments such as Boeing Service Bulletins referenced in the directive.

Key Provisions

The Civil Aviation Regulations 1998, Part 39 - 105 Civil Aviation Safety Authority Schedule of Airworthiness Directives, specifically AD/B747/41 Amdt 1, pertains to Boeing 747 series aeroplanes and concerns the fuselage section 41, stringer 6, stations 340 to 400. This directive requires operators of B747 aircraft to conduct close, detailed visual and eddy current inspections of the stringer S-6L and S-6R fuselage skin lap joints for cracks, between body stations BS 340 and BS 400, in accordance with Boeing SB 747-53-2253, Revision 3. Furthermore, operators must modify the stringer S-6L and S-6R fuselage skin lap joints between the same body stations, also in accordance with Boeing SB 747-53-2253, Revision 3. The directive references FAA AD 90-23-14 for additional guidance. Operators are required to comply with specific inspection and modification intervals based on the aircraft's flight history as of 20 June 1996. For aircraft with less than 10,000 flights by that date, an initial inspection must be conducted before exceeding 10,000 flights, followed by repeat inspections at intervals not exceeding 3000 flights. Aircraft with 10,000 or more flights as of the specified date must be inspected within 3000 flights of the last inspection in accordance with Requirement 2 of AD/B747/46. Subsequent inspections must occur at intervals not exceeding 3000 flights. Areas modified in line with Requirement 2 need not be inspected until 10,000 flights after modification. Areas modified according to Requirement 2 and Boeing SB 747-53-2272 Zone 1 may be inspected using external methods only at intervals not exceeding 1000 flights. Additionally, modifications must be carried out before exceeding 20,000 flights. Flights where the cabin pressure differential does not exceed 1.5 psi are excluded from flight counts. Failure to comply with these requirements may result in civil or criminal penalties under the Civil Aviation Act 1988 and associated regulations. The Civil Aviation Safety Authority has the authority to enforce compliance, which may include fines or other penalties. Non-compliance could potentially lead to aircraft being grounded, thereby affecting operational safety and potentially resulting in severe financial and reputational consequences for the operators. The directive aims to prevent pressure cycle fatigue, which has caused skin cracks up to 470 mm long in this critical area, leading to potential in-flight cabin depressurisation and compromised structural integrity.