AD/B747/148 Amdt 1 - Fuselage Skin Stringer 12 Lap Joint

Overview

The Civil Aviation Regulations 1998, specifically under Part 39 - 105, address safety directives for various aircraft, including the Boeing 747 Series Aeroplanes. The Boeing 747 Fuselage Skin Stringer 12 Lap Joint AD/B747/148 Amendment 1 was enacted to address the potential issue of disbonding in the waffle doubler to skin panel bonded joints, a problem identified in other aircraft types, which could lead to multi-site fatigue cracking and subsequent rapid depressurisation. The objective of this Airworthiness Directive, issued by the Civil Aviation Safety Authority, is to maintain the structural integrity of the specified Boeing 747 aircraft through regular inspections and necessary modifications to the stringer 12 lap joints. Compliance with these directives is crucial for ensuring the ongoing airworthiness and safety of the aircraft within the specified flight intervals.

Scope and Application

The Civil Aviation Regulations 1998, specifically Part 39 - 105, addresses the airworthiness directives for Boeing 747 Series aeroplanes, encompassing aircraft line numbers 201 to 230 inclusive. This legislative instrument is applicable to all operators of Boeing 747 aircraft within the specified line numbers, mandating adherence to stringent safety protocols to maintain airworthiness. It requires high-frequency eddy current inspections of the fuselage skin stringer 12 lap joints, from Body Station 520 to Body Station 741.1, to identify any disbonding or fatigue cracking that could compromise the structural integrity of the aircraft. Additionally, the directive mandates modifications to the stringer 12L and 12R lap joints, replacing countersunk fasteners with raised head fasteners, as per Boeing Service Bulletin instructions. The directive sets forth specific compliance timelines for inspections and modifications, with inspections required at intervals not exceeding 4000 flights, and modifications to be completed before reaching 20,000 flights or by 25 May 1999, whichever occurs later. This legislative instrument aims to ensure the continued safe operation of Boeing 747 aircraft by addressing known structural vulnerabilities.

Key Provisions

The Civil Aviation Regulations 1998, particularly Part 39 - 105, establish the Civil Aviation Safety Authority Schedule of Airworthiness Directives for the Boeing 747 Series Aeroplanes, as detailed in AD/B747/148 Amendment 1. This directive pertains specifically to the fuselage skin stringer 12 lap joint. Section 10/95 of the directive mandates that operators of Boeing 747 aircraft with Line Numbers 201 to 230 must conduct a high-frequency eddy current inspection of the fuselage skin around the upper row of fasteners in the stringer 12L and 12R lap joints, from Body Station (BS) 520 to BS 741.1. This inspection must follow the instructions in Boeing Service Bulletin (SB) 747-53-2366 Accomplishment Instructions, Part I. Additionally, operators must modify the stringer 12L and 12R lap joints by removing the countersunk fasteners and installing raised head fasteners, adhering to Boeing SB 747-53-2366 Accomplishment Instructions, Part III. Finally, a post-modification inspection must be carried out in accordance with the initial requirement. Operators of Boeing 747 aircraft within the specified line numbers must comply with the inspection and modification requirements outlined in the directive. Before modifying the stringer lap joints, operators must inspect the fuselage skin as per Requirement 1 before reaching 15,000 flights or within 1,000 flights after 25 May 1995, whichever is later. The re-inspection interval must not exceed 4,000 flights. After modifying the stringer lap joints as per Requirement 2, operators must conduct another inspection before reaching 20,000 flights or before 25 May 1999, whichever is later. Post-modification, the inspection must occur before 10,000 flights after the modification and must be re-inspected at intervals not exceeding 3,000 flights. The compliance dates for these inspections and modifications are crucial to ensure the structural airworthiness of the aircraft. Failure to comply with the provisions of this directive may result in serious safety hazards, such as disbonding in the waffle doubler to skin panel bonded joint, which can lead to multi-site fatigue cracking and rapid depressurisation. The Civil Aviation Regulations 1998 impose strict obligations on operators to adhere to these directives to maintain airworthiness. Non-compliance can lead to severe penalties, including fines and potential criminal charges. The exact penalties are not detailed in the directive but are stipulated under other sections of the Civil Aviation Act 1988, which may include significant monetary fines and imprisonment for serious breaches that endanger safety.